Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on December 16, 2015, 01:48:59 am
-
I've got an old abandoned project that includes chassis, populated board less transformers. Also got a board layout sketch showing component connections. It is a Marshall JCM800 pre-amp into a AB763 Fender Twin PI, PPIMV, Power amp and power supply.
So I'm counting the cost rather I want to resurrect the project or not. Looks like I will need a PT, choke and OT mainly.
So my question is, I have a huge Hammond PR-40 Organ Tone Cab power transformer and choke. Doug's Twin PT shows 345VAC on each red secondary. The Hammond schematic shows 415VAC on each of its red secondaries that goes to two 5U4GB's. So that appears to be 60VAC too much more than needed. So if I used the Hammond, I would be hooking the two red secondaries to the AB763 diodes arrangement on the board. I just need someone to take a look and verify that there is no work around to make it work??? Attached is the PR-40 schematic and the PT I have is shown in the upper left hand corner. Also I have attached a Twin layout that shows the diode arrangement that's on my existing board the Hammond PT would be hooked up to. Thanks, Platefire
-
There's usually a workaround. You can use the Hammond PT ***IF*** you use a choke input filter just like you see on the PR-40 schematic. That choke has to handle the current for the entire amp, so you can't use the typical 'twin' choke. If you put that Hammond PT in a regular AB763 power supply your B+ will be about 586VDC!
Also, the Hammond PT has no bias tap. That's OK. You just use one of the red wires to also feed the bias rectifier. Replace that 470Ω/1W resistor with a 100K/3W (actual value may even be up to 220K to give the correct negative bias voltage to the bias pot).
So, if cost is a factor, go for it. You'll need a different choke, but it should not be expensive like a twin PT. You may have to study some choke data sheets to find a suitable choke. It would be nice if you have the choke from the PR-40.
PS... That Hammond AO-63 conversion I just did had a PT with high voltage. It used a choke input power supply so I just kept that part of the circuit.
-
Thanks sluckey
I do have the choke. So that's making the project maybe have a little more potential. The choke is large enough in size where it would appear to be the size of an OT on a lot of our guitar amps. The PR-40 amp had a separate chassis for the power supply with the female 6 pin input connector from the organ/preamp, output to the power amps and the two 5U4GB's.
I actually made a console connector to the power supply by using an old battery charger chassis and installed stereo input jacks to go to G1 and G2 grids, fuse and about 10'-0 of 6 wire cord with a male 6 pin Plug to plug into the power supply chassis female socket. I used a Art Command Center Preamp/Processor plugged into my battery charger interface and played it as a guitar amp several years. I had the big cab set up in my living room. Made a nice piece of furniture. I ended up getting rid of the cab to make room for other stuff and kept the amp/power supply in the storage shed. Thank you, Platefire
-
The Hammond sports three 17 Watt amps. Total 51 Watts out.
The proposed amp is four 6L6, potentially 80W-100W out.
Are we sure the current is there? Or will the 6L6es be run below their max output?
As a *two* 6L6 plan, with two-6L6 OT, I'm sure it is ample.
-
in the stock config the 3 pairs of 6BQ5 + reverb driver are drawing ~297mA at idle [ 3 pairs 6BQ5 with Vk at 12V / 130R is ~92mA per pair + reverb driver 12BH7 with Vk at 12V / 560 is 21mA ]. power transformer is choke loaded. with SS rectifiers and choke loaded we'd probably see around 375V loaded but with plate impedance of 5U4GB we lose another 50-60V and we end up with ~330V.
with CLC filter and SS rectifiers you'll see about 580V loaded. if you use the pair of 5U4GB then PT will push a pair of KT88 at around 540V B+ without much effort. stack 350V filters. use the PR40 choke. make first B+ tap for OT AFTER choke. so you'd have: RECT-C stack - PR40 Choke -C stack then OT tap: the rest of PS taps as usual. use uF5408 diodes with at least 2 in each string. for the OT use dynaco/sunn A431S in UL form & AB763 LTPI @ ~440V and definitely use NFB - copy the fender NFB and tweak to taste. bias supply will need to be HV tapped. bias at about -80V. output power should be about 100W.
another option: leave choke input and replace the 5U4GB rectifiers with SS rectifiers or 5AR4/GZ34 and you'll bump up B+ to 375V, if you use the 110V primary tap with 120V source then that bumps B+ up another 25V to ~400V or thereabouts: YAY! 400V! the down side is you also bump up heater string voltage around 10% & you'll probably need to burn some off. if you run with the 375V B+ then a tweed twin or tweed bandmaster ckt. with 2x 6L6x would be a fit or 5E3 type with 4x 6V6. use 4K super reverb OT with either. no bias supply needed with the tweeds.
if it were mine, i'd push a pair of KT88 without even a second thought.
--pete
-
Thanks very much PRR and Dummyload for presenting possible working options.
Here is a pix of the old project. I been robbing parts off it when I was in a bind. I do have a pretty good inventory where I could put a lot back.
I see the next thing I have to do before anything else----see how close the PT hole is to end of board. I need to go ahead and pull the Hammond PT and choke and see how I can manage the real estate.
I'm not familiar with KT66 tubes. Why do you likum? Isn't that the tube that Hendrix preferred? Thanks Platefire
-
> familiar with KT66 tubes.
Where did that come from?
KT66 is a European 6L6, pretty near. Expressly made to replace US 6L6 in many ways, was for a time better than US 6L6 but now that all the old tooling is worn/lost, it's probably all off the same stampers.
DL mentioned KT88, which is a double-size 6L6. 6550 appeared so Ampex did not need thirty-two 6L6 in the first videotape machines, just 16 6550. KT88 is a nearly-same tube (usually an inch taller) in European numbers.
If you want a 100 Watt amp, a pair of 6550/KT88 is an option.
However DL's excellent rundown shows Hammond only expected 297mA at (SS) 375V, which is 111 Watts DC, and likely about 55 Watts Audio. Suggests ~~2.5K loading, which (if you can find a 2.5K 50W OT) does suggest four loafing 6L6 or two 6550/'88s. A 3.4K ("Marshall 50W") load suggests EL34 and about 40W output.
-
Hay PRR
Yes KT88, don't know where I come up with KT66 other than I'm not use to dealing with those tubes. I've been looking at KT88 on e-bay---they are pretty proud of them :laugh:
I'm not really interested in big output power. I was really wondering about the 4-6V6's and DL has covered that plus several other options. I have been reading it and trying to figure it out. PRR you right, DL did a great job of breaking down my options and man I appreciate that. That helps me a bunch!
Not saying that this is the way to go but let just explore the 4-6V6 option a little. DL, if I understood you right, you said use the Hammond choke, use the SS rectifiers for 400V B+. Is that loaded or unloaded? I assume unloaded. So I've never had to burn off heater voltage, would you do that with some resistors?? A super reverb 4K OT would work for that?
I haven't abandoned your KT88 suggestion, it's just they are kinda high and I'm a tight wad. On the other hand if you suggested them above everything else, it must be something to them. I imagine big clean power?? but only guessing. Everything I've built has been Fenerish and maybe it's time to go Marshallish. The JCM800 preamp is what's on the preamp part of the board now---with my situation would I need to go two EL34's to do that on the back end? or would KT88 be even better?
This board sketch is basically what's on the board except what I've removed for parts. So this may give you an idea what's presently on the board. The sketch was 11" x 17" so I scanned it as two pdf files. Thanks, Platefire
-
...explore the 4-6V6 option a little. A super reverb 4K OT would work for that?
yes. 4 x 6V6 -or- 2 x 6L6 - if you're pinching pennies you could sub the vibrolux OT: it's 4K 35watt, choose hammond 1750J for 4 ohm secondary or 1760J for 4-8-16 secondaries.
if I understood you right, you said use the Hammond choke, use the SS rectifiers for 400V B+. Is that loaded or unloaded? I assume unloaded.
yes, use hammond PR40 choke
yes i'm assuming slightly over 400V at idle and loaded with 120VAC applied to the 110V tap. in this plan, you'd shave off a volt or thereabouts of filament supply voltage. use resistors calculate value with ohm's law.
with 120V to 120V primary & SSR you'll be close enough to 380V to build a tweed twin type 2 x 6L6G power amp or "super" tweed deluxe 4 x 6V6 amp.
test PT on your bench and work with care:
1) apply 120V to 110V primary tap. it's the pair of wires of the three primary wires that have the least DC resistance and record the DCR of 120V & 110V windings;
2) measure filament windings AC volts and record values for both of them the 5V and the 6.3V;
3) measure HV winding AC volts: measure HV winding from CT to end and record: don't measure HV winding AC volts end to end as you may exceed your DMM's input rating;
4) measure the DC resistance of the HV winding end to end and CT to each end and record;
apply 120VAC to the 120V primary and repeat steps 1-3.
--pete
-
Plate, sorry for jumping in so late. I built an amp using one of these and used an input choke. I used 4, 6v6 tubes and an AB763 with verb. I have to say it plays cleaner than any other amp except a Standel and I would bet if I changed the PI to a 12aU7 and used a JBL it would be just as clean.
I was very happy, but it was too heavy. It sold the same day I took it to the music store. Did I say I put it in a 2, 12 Cab with 2 vintage 30's. Thing weighed in at a whopping 88lbs and I did not put casters on the combo. :l2:
If I may make a suggestion tho. If I were to do it again and I do have another one, I would just use 2 KT88's. I have built 2 KT88 amps now and absolutely love them. I also have plenty of 6550 Winged C and some original TungSols as I have repaired Leslies for a while now. They have a very unique tone for guitar and you will have something different. There is absolutely no mud when using these tubes, that is unless you want it.
The tone and frequency response is better than a Twin IMO.
Good luck with you build, just thought I would chime in and say HI.
-
DL, got the PR-40 Power supply chassis out this morning plus also my PR-40 Guitar Preamp/fused power supply Interface that I made years ago to hook guitars up to PR-40's through 6 pin connector that came from the organ(but now my interface) to the PR-40 power supply chassis. So I got it hooked up and it's working.
I am trying to perform the test you outlined as follows:
1-I'm still a little confused on this one. On the PR-40 schematic, it shows the two red primary taps that the hot and neutral 120VAC hook to. Also on the sche shows the center tap labeled "HO". So if I'm understanding you right, you want me to measure DC resistance while it's hot! I'm not understanding--" measuring the DC resistance of the 120 & 110 wingdings". Please elaborate on that a bit more---with it being measure hot, I don't want to hook up wrong and blow something up.
2-Measurements on the two yellow wires is 5.39VAC and the one connected to the choke is 6.10VAC. Heater voltage is 3.90VAC per side, 7.79 combined.
3-Little confused about this one to. When you say "HV" is that High Voltage? With the MM grounded to chassis and reading the secondary ACV is 455VAC per side. Also there is a tap called "-HV" I'm assuming to the bias circuit, it reads 50VAC.
4-Is this measurement to be done hot or not? Measured not hot with the rectifiers pulled, MM ground to chassis and MM red to rectifier pin #4=24.8 Ohms and to pin #6=27.5 Ohms. 52.4 Ohms end to end. If I did it wrong please tell what I need to do to correct.
BTW-I measured the unloaded B+ with both 5U4's in there and it was 473DCV. All the above measurements was made with everything wired up Hammond style it the chassis. If I need to cut the wires loose to the rectifiers/chassis to do the measurements, just let me know. Thanks, Platefire
-
please measure DC resistance WITHOUT power. never try to measure resistance in powered up circuit. you can fry the DMM/meter.
--pete
-
forgot to mention - remove the tubes and discharge caps.
seems that there are two versions - the PT you have doesn't have the tag-board on the end-bell. your PT may not have the 110V tap?
so you do have a 50V tap. if that's the case, then it can be used for 6L6 or 6V6 bias, however, it won't work for 6550/KT88, however, you state that you're leaning to 4 x 6V6 so that's a plus.
looking for pics i found an old ad on ebay for a pr40 amp. made him an offer, he accepted and so it's on the way. i want to experiment with a choke loaded supply and this one is perfect. the bounty of 6BQ5's is a bonus. thinking i'll convert mine to SS recto or GZ34 and run 2 x 6L6 for starters, then experiment with 6550/KT88.
--pete
-
it won't work for 6550/KT88
can you help me with this? Is 50vAC, to low for fixed bias 88's?
-
it won't work for 6550/KT88
can you help me with this? Is 50vAC, to low for fixed bias 88's?
what plan? 100W? 50W? B+?
dopends on the mode. pentode mode, yes marginally and dependining on B+, triode mode of any use no, UL mode likely not.
for UL you really meed 60-70VAC winding. 100W UL spec calls for 550V and 80V g
bias.
you could use half wave doubler. i don't trust them. use an ancillary transformer for bias if 50V tap won't work.
--pete
-
DL, I think everything I previously told you about the PT primary's was wrong!
I now see what you mean about the 110V primary tap and 120V tap. Because the schematic PT wiring is not color coded to match the PT wiring in the amp, its a little hard to figure out which is the 110 and the 120 tap. There are three primary taps, two black and one brown. One of the blacks go to a terminal strip that's not connected to anything. So this is the resistance reading between those taps:
The black and brown that's connected to 120V is 1.5 Ohms between them.
The Connected Brown to the unconnected Black is .3 Ohms between them.
The connected Black to the unconnected Black is 1.4 Ohms between them.
On the schematic it shows pin #3 of the 5 pin connector from the console connected to the 120V tap primary. The one Black on my amp is connected to to pin #3 also.
On the schematic it shows pin #4 of the 5 pin connector from the console connected to the tap on opposite end of the primary winding from the 120 and 110 taps. The brown wire on my amp is connected to #4.
I measured voltage between pin #3(Black Primary) and #4(brown Primary) of the five pin connector with it connected to AC house voltage and it was 120VAC between those two primary taps. So these two taps is what's connected to power.
So with the above info, if you will identify which is the 110V tap, I will apply voltage to it and make the readings you ask for in replay #8. So is the un-connected black the 110 tap?
Another thing regarding secondaries that was wrong is, there is no bias tap. All three PP EL-84 amps in the PR-40 is cathode biased.
I just imagine you was confused after reading my last post for item #1 for your requested measurements and I hope this clears some things up. Thanks, Platefire
BTW-I'm starting to think about a 50 watt Marshall. The large PT is crowding the area where the last two octals would go, so two EL-34's in the middle. The bias voltage comes right off the secondary. Something like this:
-
So is the un-connected black the 110 tap?
yes, i believe that it is. use a lamp limiter if you test with 110V tap.
--pete
-
Well thanks pete for your reply.
I was kind of hoping to do the 50 watt Marshall with two EL34's but as you indicated about the heater voltage already high at 7.79V and going higher with the 110 tap. Also the EL34 would require 400V loaded plate voltage and with the 120 tap would be running 370V to 380V would be low for the EL34. Regardless, I was planning to do SS/diode rectification on this one.
I did some measuring last night and checking my real estate. I'm not sure if I can use the two further most octal socket cut outs because the large PT will be right up against those tubes if used. It appears the tube will be within 1/2" of the PT. That might not be a big deal? but I've always tried steer clear of that. That's why I was thinking about the two middle octal slots for two EL34's or 6L6's.
So it appears the only way to get the loaded voltage up enough to do that is by using the 110 tap or a voltage doubler---right? So it will be Monday before I'll have opportunity to test it further. So if you think there is a work around for the higher voltage, I will test the 110 tap then and post the results.
If the 50 watt Marshall is out of sight, I'm sure I can juggle the PT around someway to get clearance to do the 4-6V6 thing. Thanks, Platefire
BTW-I can't believe you have picked up a PR-40amp. I've had two. Nice speakers, tubes, transformers and cab. Lots of parts to scavenge off of that! Do you recognize the part that I used to install a MV and hot switch in the pix??
-
Ed
Just wanted you to know I haven't ignored your post, just been real busy :happy1:
I might end up doing the 4-6V6 thing but for some reason I've got interested in a 50 watt Marshall. That's something completely different than I've ever done and I've never owned a Marshall amp--so this would give me a little taste.
Did you make a schematic of your AB763/Super 5E3 power amp? Did you fix bias or cathode bias it? One channel input? At this point I think my voltage levels will be to low for the two PP KT88's. You and DummyLoad both recommending them has got me wondering about a KT88 sound.
So I'm not sure which way the amp is going to go, but will definitely be going. No hurry, I love piddling with this stuff :icon_biggrin: Platefire
-
I did some measuring last night and checking my real estate. I'm not sure if I can use the two further most octal socket cut outs because the large PT will be right up against those tubes if used. It appears the tube will be within 1/2" of the PT. That might not be a big deal? but I've always tried steer clear of that. That's why I was thinking about the two middle octal slots for two EL34's or 6L6's.
use the two holes next to the PT for can caps. JJ or F&T 1-3/8" cans will fit nice in those holes.
--pete
-
Yes, could do that. Think for now I will concentrate on getting the big PT and choke mounted. Then get power cord, power switch and fuse holder installed. At that point it might be a little more obvious with what room I have left, what to build in that space. After all the big Hammond choke belly will have to be cut into the chassis just like the PT. That may have an impact on how my board will be situated. May have to build part on board and part terminal strip P to P. Platefire
-
You can easily put some small "L" brackets on that iron and stand it up to avoid cutting big holes. That will free up a lot of real estate under the hood. Does the PT and choke have bell covers on each side of the laminations?
-
Well this is what it looks like on top and going through the PR-40 power supply chassis.
-
I would get 8 L brackets and stand both of those up.
-
So your saying to change the mounting style from flat to Horizontal? Who handles the L bracket footings?
Like this or that?
-
Lowe's has a good assortment. 1/2 x 3/4 x 3/4 is what I've recently used for this same purpose. Should be able to find them in any hardware store, even Walmart...
http://www.lowes.com/ProductDisplay?partNumber=315714-1277-DPB115&langId=-1&storeId=10151&productId=3169855&catalogId=10051&cmRelshp=rel&rel=nofollow&cId=PDIO1 (http://www.lowes.com/ProductDisplay?partNumber=315714-1277-DPB115&langId=-1&storeId=10151&productId=3169855&catalogId=10051&cmRelshp=rel&rel=nofollow&cId=PDIO1)
-
Thanks sluckey for making me aware of that. Never done that before on all my conversions. Doing that may allow me to use the existing board made for that chassis with a few alterations for what ever circuit. Those huge things(PT/choke) will look kind of funny and top heavy jacked up so high, but sometimes extraordinary situations calls for extraordinary action. I think that will be next thing on my list to work with the intention of making it work. Not sure how it will work around that big gaping hole for the old PT, but I have built cover plates before for such holes. Get the L brackets, put them on and work it from there!!Whatever it takes, git r dun :thumbsup: Platefire
-
Ed
Just wanted you to know I haven't ignored your post, just been real busy :happy1:
I might end up doing the 4-6V6 thing but for some reason I've got interested in a 50 watt Marshall. That's something completely different than I've ever done and I've never owned a Marshall amp--so this would give me a little taste.
Did you make a schematic of your AB763/Super 5E3 power amp? Did you fix bias or cathode bias it? One channel input? At this point I think my voltage levels will be to low for the two PP KT88's. You and DummyLoad both recommending them has got me wondering about a KT88 sound.
So I'm not sure which way the amp is going to go, but will definitely be going. No hurry, I love piddling with this stuff :icon_biggrin: Platefire
Build your marshall if you don't have one. Here is my weird methods of building today. I mainly build power amps and separate preamps. Then I always have schematics and I do mostly point builds. Cathode bias for everything 30 watts. On the KT88 I have done UL with fixed adjustable (Marshall type bias) and also cathode bias as in the Leslie 147 with 6550 tubes and I paired a set of KT120's in a build as well.
I now have quite a few Power Amps with different tubes and some different PI's. I just sold off a herd of amps I built and don't want to get anymore unless I run into a preamp/power amp I really love. I guess what I am saying is I have all the complete amps I want and just like building different stuff.
Unless I am working on something I plan to put into a head cabinet and pair up with a speaker cab, I do not draw it. I am currently working on a 4 6V6 amp that I am drawing a schematic and layout for, but it has an overdrive, dual input tubes, verb and tremolo and this makes it where to me drawing it out is needed. Most of the stuff I like, Sluckey has done something similar and I simply revise his Visio files for my needs.
A cranked KT88 is a wonderful thing if you can stand the volume. Their distortion is so smooth you really don't know it is happening until you are wiggling your fingers and it just keeps on going and they tend not to squeal very easily. I have quite a few Marshall variants and love them. Jimbob is always chanting about the KT88 Major as well. I am sure you are familiar with old Purple so you know the sound of the tube.
I also have a Hammond JR-20 which originally used 2 OT's. one for Treble and one for Bass. I converted it to a dual OT reflected 10K to 8 ohms as I had 2 Stancor OT's and used the Choke input. I have a 6G6B preamp build I put in front of it and that is what gave me the idea of my current project that I have been working on for over a year now. I only have the schematic and I have not completed it yet, but I am close. I really like the Iron from these things and the JR20 has an alnico 12 it uses for bass and the good ones were made by Hepner, but when you find the Hepner the 4 10" are Magnavox :w2: and are not guitar friendly, but the hepner is a great speaker.
-
Mounting transformers like this will be plenty strong. Lot's of transformers mounted this way. If you get serious about this, consider making an oversize cover plate. That will allow you to move the PT and/or choke around to suit your layout. Kinda like this...
-
Ed---I haven't heard anybody doing it that way, with separate preamps and power amps. One thing for sure, it would be easy that way matching up different preamps and power amp to see how they work together. From all you have built, what was your favorite preamps and power amps separately and which made the best match joined together? Tell you what, I'm really impressed with the Ampeg Gemini II pre I installed in my Bogen CHB-20A. That was a departure from my norm that sluckey introduced me to.
I've been mostly tweaking my old builds. I have a little bit more knowledge now, so I trying to apply that to even making my old builds better. I got several others that need help :help: . I'm really happy with the improvements made on the last two I've re-worked. So that's encouraging. I really don't need more amps or guitars either for that matter. I have however started this build out of spare parts. It's like they are calling my name--"put me to good use" so I guess i will.
Thanks for describing the KT88 operation. That must be a sweet sounding tube but sounds way louder that I could use. I think you lost me on "Jimbob and "old Purple"?? unless you are referring to old Deep Purple? May need to q me in :icon_biggrin:
So you've got an old Hammond project going on for a year now. The treble and bass OT's remind me of my PR 40 amp that has two treble OT's and one Bass OT. I've been told they wouldn't make good guitar OT's--but can't remember why? So do you have a thread for this build that your getting close to completing? I can't imagine how you used two OT's not being stereo? I never heard of hepner speakers, so that's a new one on me. Thanks, Platefire
-
Sluckey
Checked my metal plate inventory today and what I got is in the 22Ga area. Seems kinda thin for this application. Think I may need at least 32Ga/ 1/16" thick. About a 5" x 5 1/2" would do it. I will be going by LOWES tomorrow and I'll check plates and L brackets.
22Ga might be Ok after being bolted down and stiffened up but I would feel better with 32Ga. Platefire
-
32ga is thinner than 22ga.
Strange but true.
What it is: the gauge number is sorta the number of times it has been beaten-down. I'm not clear on sheet techniques but I know some about wire. Wire starts as 1/4" rod. The first pull through a smaller hole gives #1 gauge, next pull gives #2, etc etc. #40 (pickup wire) is a lot of slim-down pulls.
Sheet probably starts from 1/4" or similar plate. Sheet gauges are not the same as wire gauges, but not-so-different, and go in the same direction.
(For practical reasons, electric wire over about #10 is never solid, always "stranded" out of 7 or more smaller gauge wires.)
-
Ed---I haven't heard anybody doing it that way, with separate preamps and power amps. One thing for sure, it would be easy that way matching up different preamps and power amp to see how they work together. From all you have built, what was your favorite preamps and power amps separately and which made the best match joined together? Tell you what, I'm really impressed with the Ampeg Gemini II pre I installed in my Bogen CHB-20A. That was a departure from my norm that sluckey introduced me to.
I've been mostly tweaking my old builds. I have a little bit more knowledge now, so I trying to apply that to even making my old builds better. I got several others that need help :help: . I'm really happy with the improvements made on the last two I've re-worked. So that's encouraging. I really don't need more amps or guitars either for that matter. I have however started this build out of spare parts. It's like they are calling my name--"put me to good use" so I guess i will.
Thanks for describing the KT88 operation. That must be a sweet sounding tube but sounds way louder that I could use. I think you lost me on "Jimbob and "old Purple"?? unless you are referring to old Deep Purple? May need to q me in :icon_biggrin:
So you've got an old Hammond project going on for a year now. The treble and bass OT's remind me of my PR 40 amp that has two treble OT's and one Bass OT. I've been told they wouldn't make good guitar OT's--but can't remember why? So do you have a thread for this build that your getting close to completing? I can't imagine how you used two OT's not being stereo? I never heard of hepner speakers, so that's a new one on me. Thanks, Platefire
Yes, I am speaking of Deep Purple. I really Ampeg Preamps TOO! I actually have a B12 Bass preamp and it sounds great into a Push Pull 6v6.
It is not the hammond stuff I have been working on for a year. I ran across a 62 Bassman a couple of years ago and fell in love with the preamp, so I have to say I prefer plate driven side tone stack. I have also been messing around with signal pentodes a lot. I finished a mod this morning and cannot get the photos uploaded as they are on my phone and the forum will not accept a .jpeg, just ,jpg. I will put them up later.
The amp I am working on is just like a 63 Vibroverb with an added EF86 overdrive, but the PA section is 4, 6v6. Something about having 4 output tubes that to me enhance and give a fullness you cant get with 2 tubes. I like the Brown tonestack simply because it sounds similar to boosting a Blackface. It adds just a little hair and spank and I love the reaction of the treble. I wish I could get some more of the real 350K/tapped pots, but I read on another forum where Tubeswell posted an alternative design and it works well. Not the same, but close.
I have a 68 Super Lead 100 Watt of El34's and a 50 watt built exactly the same, but the clean tone is much better with the 100 watter. I don't know what it is, but there is something to it.
This morning I changed a JTM45 to KT66, added another hole and have 2 inputs to 5879 tubes. My OT is not the proper one so I am running the amp 4 ohms into an 8 ohm cab and reflected I have 6.8K, so I ordered an 8K multitap a little bit ago. The amp sounds great. I have a couple things left to do, but will do them when I get the new OT. I was surprised that the volume is not unmanageable.
I have one of the 5879's on the bright channel bypassed with a 3.3uf/2k2 and it acts like an overdrive when jumped. I have yet to finish tweaking, but it is a winner. I want to cascade switchable, so I got some relays to figure out.
Even though I sold a lot of my amps I still have a lot. I have built preamps for a Blackface with verb, a Gibson GA40 and a 5B3 all in the same chassis, one of those blank stout chassis. It is according to what I am playing, but I have to say my favorite preamp is 6sc7 driving a Brownface 6G6b Tonestack.
It is big, fat and hairy. Gotta love anything that is described like that. :l2: I get more touch with the Octal pre tubes seems like.
Sorry for so much writing, hard to narrow it down really. I have found I prefer less gain in V1 for my normal fingerstyle.
-
Your right PRR, don't know what I was thinking about---going the wrong direction. I use to be a Draftsman in a Trailer plant(Nabors Trailers) 30 years ago and knew all the gauge sizes in fractions of an inch and decimals(16Ga/1/16"/.0625). This proves I'm a little rusty.
I did go to LOWES and found a piece of 16Ga x 6" x 18"($7) that I think is just right. It is unfinished steel, so I will have cut it off, Smooth off cutting edge, prime and paint it or it will rust pretty quickly.
Also found the 1/2"wide s 3/4" x 3/4" "L" Brackets by Stanly and just sizing them up(eyeballing them) with the choke and transformer think they will work just fine. The corners are not rounded off, so I think I'll have to round off one inside corner on each one with a file--easy fix.
It will be a little work to get the plate cut out, finished, mounted and then re-drill to get PT/Choke mounted vertically but when that's done I should have a lot more room to do what I need inside. Thanks, Platefire
-
> a Trailer plant (Nabors Trailers) 30 years ago
http://forum.aths.org/85866/Nabors-Trailers?PageIndex=2 (http://forum.aths.org/85866/Nabors-Trailers?PageIndex=2)
http://forum.aths.org/Attachment15932.aspx (http://forum.aths.org/Attachment15932.aspx)
-
Yeah PRR, that's it that you referenced. Spent about 14 years there. My specialty was Low beds with detachable goose-necks. I also did pole trailers, flat beds, refrigerated truck bodies and moving vans but low beds was my specialty. The ones that haul the big cats and such equipment. I quit there in 1981 and went to work for Federal Government/US Army and stayed there 29 years--so 43 working years. The old original plant closed and one of the salesmen obtained the rights to the name and started his own Nabors Trailers on I-49 about 20 miles away. He latter changed it to his own name "Blackman" trailers but I don't know if he's still in business??
Glad to be building tube amps with 16Ga patch plates now :dontknow:
-
Had a great Blessed Christmas day, Children, Grandchildren, in-laws and a few outlaws! :laugh: Cleaned up the mess today and after a little relaxing swung back into amp mode.
Put the "L" feet on the PT and choke. Kinda sliding them around on the chassis trying to get best mounting position. This is my first thought with choke over existing grommited choke wire hole and PT positioned for easy tie in of red secodaries to diodes on end of board. I mostly thinking this way due to the wire exit holes and diode rectifier. If I was doing tube rectificatuon, I would face the Bell wire outlet toward the tubes. This look OK? Platefire
-
suggestion: rotate the either the choke or the PT 90 degrees, that way the flux in the PT winding window won't couple with the flux in the winding window of the choke.
--pete
-
my PR40 arrived this morning and it's in really fine condition. the amp & PS came with all the tubes.
first experiment:
no significant mods, other than the male 5 AC input was cut out and an IEC with fuse-holder installed. configuration is a stock choke loaded PS with the stock 50uF filter. i built a SSR octal socket adapter with 4 1N5408 diodes (see pics) and built a 4K 80W load bank. i estimated about 400V: real world is 386V. so 386V/4K is about 97mA or about 37.3 watt load. yes, the resistors got little warm: IR thermometer indicated that they were at about 135degF.
i ran a HV winding tap to one of the terminals strips to allow for a bias supply experiment as well. i'll post results of that tomorrow.
https://www.dropbox.com/sh/gw86gzvyacjujf5/AAAXWLa9ZAzU2bIAg-mWiCaZa?dl=0 (https://www.dropbox.com/sh/gw86gzvyacjujf5/AAAXWLa9ZAzU2bIAg-mWiCaZa?dl=0)
--pete
-
perhaps this is the ticket... makes sense. EL84 >> EL34.
--pete
-
I really like that old Hammond stuff. Always seems to be high quality stuff put together very well. I'm waiting for some unmolested pics of the amp.
-
Platefire, I would hold off on drilling any mounting holes for the PT and choke until I could put an OT on the chassis too. Then you can move them all around to see how they will fit. Sometimes you will find the OT mounted beside the PT like this...
(http://www.ceriatone.com/images/completeAmps2014/2204_TAD/amp_2B.JPG)
Other times you may find the choke mounted beside the PT like this...
(http://sluckeyamps.com/ac15.jpg)
I would probably drill a hole in the bell cover for that choke to allow the wires to exit on the bottom (just like the PT). Completely remove the bell cover to do any drilling!
-
I really like that old Hammond stuff. Always seems to be high quality stuff put together very well. I'm waiting for some unmolested pics of the amp.
link to some hi-res. shots of the amp chassis.
https://www.dropbox.com/sh/b04p7trqpjke5n0/AACE7QXji5rTcc2LgkAEucrza?dl=0 (https://www.dropbox.com/sh/b04p7trqpjke5n0/AACE7QXji5rTcc2LgkAEucrza?dl=0)
think, i'll leave this one alone. the power mod is fair game, but the chassis is in such good condition it'd be criminal to dismantle. i have the original sylvania and RCA tubes that came with it stashed as well. saving it for a PR40 cabinet that will need the service.
--pete
-
think, i'll leave this one alone
I don't blame you. That does look nice!
-
ok last of the experiments for a while. i need to get back to amp building. i need to finish one for a friend who also works on my M/C.
this looks good for a pair of EL34 in PP with a 3.5K load. use the marshall 3.6K from classictone or the marshall jcm800 50W from doug at 3.7K for slightly less power. datasheets say 48W with a 3.5K load with 375V B+.
the HV tap bias supply attached as shown has a span of -27V to -44V. to the B+ supply i added a 100uF dual can and another RC filter stage.
please see attached schematic for clarification.
--pete
-
link to pics of experiment.
https://www.dropbox.com/sh/39jd7u0vjyj0jhz/AADuoceUrd5S7MVStwpgiHLUa?dl=0 (https://www.dropbox.com/sh/39jd7u0vjyj0jhz/AADuoceUrd5S7MVStwpgiHLUa?dl=0)
one pic is bias pot at ~~ center, the other two are with bias pot at maximum and minimum.
--pete
-
Wow! Things have been happening while I was out :icon_biggrin: Trying to take it all in :think1: pete, the PR-40 you got in there looks like it just came out of the factory--clean. Both of them I got came from where I use to work, Fort Polk, La. And I happen to know they sat in an abandoned WW2 Chapel for years before the government decided to dispose of them--a lot of dust collecting! When they finally tore down the buildings, they had to do something with them then.
I'm totally blown away with how fast you moved out on this amp, modded the power supply and did a simulated load test, hooked up a test bias circuit and produced a schematic. How cool is that? beyond comprehension! Thanks! According to the way I'm seeing your experiment/calculations, everything it clear for a PP EL34 amp. So looks like a 50 watt(almost 50) Marshall is a go. So like you say, I need to choose an OT 3.6K to 3.7K with multi-tap Ohm. All of my speaker loads are 8 Ohm. I'll check out the sources you said.
sluckey, don't worry, I don't want to get ahead of myself of this one. I'm holding off doing much more until I can decide what Marshall circuit and get a plan together. Don't know much about which is good or bad regarding Marshalls. I know there is a lot of talk about a Plexi. I've been looking at the Marshall pre's with the low/high gain inputs and the way they do it through the input jack switch. Seems like to me it would be better to use a switch(or foot switch) to add the gain stage and stay plugged in. Also with 50 watts I think I need a MV and thinking post PI MV with dual 1 meg pot. Like you say, also need to get my OT on board in the planning stage. I have schematics on the plexi and 2204 looking them over. Would appreciate advice about the right Marshall circuit. Thanks, Platefire
-
how about JTM 45 with EL34 (JTM50)?
http://www.classictubeamps.com/schematics/Marshall/JTM50.pdf (http://www.classictubeamps.com/schematics/Marshall/JTM50.pdf)
-
plate, there is something else to consider before you start building: when you fire up a power supply with choke loaded PT with no load, the B+ shoots up to near that of a capacitor loaded PT.
with the tube rectifiers replaced with SS, the B+ shoots up to over 540V until there there is a respectable load - IOW, you have 540+ volts of B+ until the tube heaters warm-up and provide the load. with tube rectifiers, the power amp heaters have already started warming up when the rectifier tubes are warming up, so the overshoot is near non-existent.
IF you use 450V or 500V caps, you risk damaging them unless you have permanent dummy load built into the PS to keep the B+ overshoot in check until the heaters warm-up. there are other work-arounds: use 600V caps, or a series cap stack(s), or use a pair of 5AR4 tube rectifiers with slightly less B+.
do not use a standby switch if you use 5AR4 tube rectifiers with 450V/500V caps.
--pete
-
plate, i ran my breadboard up with this PS just little while ago. i have a 4K fender OT connected. with bias at -32V i get 375V B+ with about 36mA flowing per EL34. sounds decent enough for 44W. the cut sheet says 44W with a 3.5K primary. it's loud, and it sounds fair enough, however, i'm driving it with a standel 25L15 preamp that was driving 4 x EL34 at 100W for maximum headroom. i was tearing the standel experiment down anyway so swapping in the PS mod and OT was a minimal effort.
to alleviate the high B+ power-on surge issue i installed a pair of NOS sylvania 5AR4/GZ34 rectifier tubes. seems happy and it's relatively quiet even with all the damn wire running all over the place. surge at turn on peaks at about 415V as observed with my DMM. you could probably get away with one GZ34 with a loss of just a few volts of B+
please see attached schematics.
link to pics of experiment below:
https://www.dropbox.com/sh/39jd7u0vjyj0jhz/AADuoceUrd5S7MVStwpgiHLUa?dl=0 (https://www.dropbox.com/sh/39jd7u0vjyj0jhz/AADuoceUrd5S7MVStwpgiHLUa?dl=0)
--pete
-
My satellite internet system is running so slow way back here in the sticks that the pictures to your dropbox won't open, so I'll guess I'll view them later!
Thanks for doing that experiment and doing the schematic. I'd say that is a good pre-view of how my amp will behave with the bias set up like that, two PP EL34's and two GZ34 rectifiers. I have no problem running the two GZ34's but it's going to be hard to live without a standby switch :BangHead: I think this is a conspiracy between you and sluckey :l2:
Hay, the two extra octal socket holes are there already, why not use them. Wow, I think that pretty much lays out the power section. I checked on the Classictone #40-18025 3.6K OT and they are on back order. They say it will be a week or two. Thanks a bunch :notworthy: Platefire
BTW-Think I will take your experiment schematic and draw a proposed preamp :think1:
-
OK, here is the schematic of what I think I want to build. I adapted DL's schematic and married it up with 2204 schematic with Doug's hot switch without relay. I know I've got stuff wrong, but not sure what. Please check me and let me know what's messed up. The Marshall schematic had filter caps prior to the choke and in DL's model only after? so I wasn't sure so I threw some in like the 2204 schematic?? don't know if that's needed?
I changed the V1a & b cathode resistors and caps like Doug's hot switch because he said it was voiced to not have too strong of a bass or treble effect on the signal. That sounds good to me however I haven't had much experience playing over Marshall value pre's. So this is what I envisioned making out of it---rather what I got will sound good and work right, I don't know? Platefire
-
1) BIG error! - you have a capacitor loaded PT. the 50uF/50uF caps are connected AFTER the choke.
2) there is no junction at 100K NFB resistor & .022uF PI coupling cap. the 100K NFB resistor connects to the 10K tail & presence pot.
3) LTPI non-invering AC ground cap should be .1uF not .022uF
--pete
-
Thanks pete! I think I've got it corrected, please check me out. I have grid resistors shown prior to the power tubes but didn't put a value on them because I could not find an example of that on any of the 50 watt Marshalls. On a 100 watter it looks like they had 5.6K if I was reading it right?
Also, should the NFB be connected to the 4 Ohm tap even though I'll be using the 8 Ohm tap?
Appreciate you help, Platefire
-
Plate you moved the the caps after the choke that's right, but what's going to filter the A node B+?
-
Willabe
If you go back and read DL's last response, be said the PT is capacitor loaded. So I'm not familiar that and didn't know until he told me.
-
Plate in your newest drawing there in no filter cap or choke filtering the B+ A node. You have to have 1 or the other.
-
Look at the drawings in DL's reply #49. :icon_biggrin:
-
OK, Willabe--let's try this again and see if I'm getting closer to home :undecided:
-
this should work... please pardon, i cleaned up the draft a bit and rebuilt the B+ filter string.
respectfully,
--pete
-
Wow! So we're pretty much there! Yea! That was a sweet clean up job DL on the Sch, thanks! As fast as you move with these schematics I can tell you have become pretty skilled using the PCB/Sch program---I'm still pretty slow with it. Thanks so much for helping me get this plan together and now I have something solid to go forward with for the build process. So let me see now, hmmmm :think1: parts---layout--->>>>>>> :happy1:
-
we forgot the grid stoppers for the EL34s. the EL34 symbols had the wrong pin-outs and the G3 connections to the cathodes were missing (pin 8 to pin 1). more clean-up and i added reference designations to all the parts, (e.g. R1,C1, etc..) to facilitate troubleshooting, if needed. lastly, i created a BOM from the schematic - another good reason to add reference designations to the components.
please review the attached revisions & BOM.
--pete
EDIT: uploaded corrected schematic and BOM.
-
Hay Man, that looks great! I was wondering about the grid stoppers but didn't know what value to put in there. The older Marshall schematics didn't have any. So the schematic and BOM is top notch and I didn't see anything that needed fixing, thanks!
I determined last night that I wouldn't be able to re-use that old project board for this project. so I've been working on a new board layout using ExpressPCB. I've had that on my computer but never used it. I've only used ExpressSch for schematics, not boards. So I'm drawing it to scale so I can determine how much board material and turrets I will need, plus having a board plan for drilling.
I think in the area of the PT, I'm going to need to mount the PT and run wiring to the rectifier sockets, fuse, power switch and power cord to determine what kind of room is left in that area to install my filter caps/power nodes and bias circuit. Platefire
Edit: I do have a question on the schematic. I noticed you change the bright cap value on the tone stack treble cap from .0005 to .022? The values that were on there was from the attached 2204 schematic. Just wondering why you changed that?
-
so sorry that should be a .0005 cap. cut and paste error. I'll fix it shortly.
--pete
EDIT: fixed and resubmitted please download new .sch and .pdf in reply 61. i'll fix the BOM and upload i a bit.
-
OK, Thanks! Got the new versions.
-
Any reason a bias circuit can't be adjacent to filter caps/power nodes? To be more specific AC feed from PT secondary to bias circuit 220K dropping resistor within about 5/8" away from "E" power node cap & resistor turret. Platefire
-
Any reason a bias circuit can't be adjacent to filter caps/power nodes? To be more specific AC feed from PT secondary to bias circuit 220K dropping resistor within about 5/8" away from "E" power node cap & resistor turret. Platefire
that should be ok, just keep the filtered output connection(s) to bias tubes ckt. away from AC, HV or filament.
--pete
-
OK, Thanks. Happy New Year! :guitar1 :m5 :m7
-
>>> Happy New Year! :guitar1 :m5 :m7
back at ya! ...and good luck with this endeavor.
--pete
-
Thanks! When I get my board/layout plan done, I'll post it for public ridicule :l2:
It helps IMHO being able to draw it to actual scale you can actually tell
How much space your taking. The only problem is I can't print it out full scale so I can use it for a drilling template. When I was working I had access to better tools to accomplish this type of thing--especially when it comes to high end CAD programs and large printers. You have to realy get inventive with the ExpressPCB to do everything needed. Still I'm thankful of what I do have. Thank you Jesus for another year! Platefire
-
Got a question in the back of my mind I need to settle about this project. Haven't had any experience with EL34's but always thought of them as a high plate voltage operator. When I discovered my plate voltage with a load on EL34 would be around 380VDC, I was thinking that's kind of low, more in the range of a 6V6 but I thought, on the other hand it may be OK.
Last night I downloaded a EL34 spec sheet and one of the first thing I noticed was a 800VDC max.
This one is not going to be even half of that. So my concerns is will 380VDC be enough to tickle that EL34 to wake it up a bit? :dontknow: Just wondering about that before I start ordering parts. Platefire
-
Got a question in the back of my mind I need to settle about this project. Haven't had any experience with EL34's but always thought of them as a high plate voltage operator. When I discovered my plate voltage with a load on EL34 would be around 380VDC, I was thinking that's kind of low, more in the range of a 6V6 but I thought, on the other hand it may be OK.
Last night I downloaded a EL34 spec sheet and one of the first thing I noticed was a 800VDC max.
This one is not going to be even half of that. So my concerns is will 380VDC be enough to tickle that EL34 to wake it up a bit? :dontknow: Just wondering about that before I start ordering parts. Platefire
plate, a pair of EL34 will make 48 watts with 375V. refer to the mullard or phillips data sheets. you can run them at 600V+, however, they are unreliable at those voltages. a simple mis-matching of load can cause arcing between elements (pin2-3 arc is the most prevalent) or even a poorly implemented standby switch can also cause arcing with high B+ amps.
http://tubedata.milbert.com/sheets/129/e/EL34.pdf (http://tubedata.milbert.com/sheets/129/e/EL34.pdf)
yes, you could run a quartet of 6V6 for about 40 watts, but why?
things that we build with larger pentodes are best kept at or under 500V B+.
--pete
-
OK, I see--Pentode, fixed bias, push pull=375 to 400VDC. I figured it was just my lack of knowledge
but at the same time I had to ask the question so I could get the little nagging questing out of the back of my brain. Thanks, that clears that up--have no desire to run anything other tube than what we planned for. Still working hard on the layout plan. Thanks, Platefire
-
my plate voltage with a load on EL34 would be around 380VDC
My last build *copied* the matchless clubman PA section, B+ about same as you(380vdc).
It's self biased, so I'm around 25W into a 2X12, fixed bias should get you more.
Mine is LOUD! and sounds very nice, I started with 88's but liked the 34's sound better.
fwiw
-
> a 800VDC max.
As said.... that's frickin' dangerous.
Philips was anxious to improve sales. Most other octal tube makers thought 800V on the Octal base was "very aggressive rating".
At 775V you "can" get 100 Watts per pair. There was a professional amplifier working at this level. It was part of an even larger amplifier(!) so the need for strict regulation and load-control was absorbed in overall general expense. But EL34 is also a low-price tube, and you have to wonder if four bottles at 400V might have been a safer design.
Obviously Marshall et al felt that 4 jugs for 100 Watts was a fine design.
The EL34 is perhaps more able to suck hard at low plate and screen voltages than the older tubes like 6L6.
> 48 watts with 375V
Or at lower load, 44W with 350V.
11 Watts SE with just 250V plate and screen (265V supply).
-
Sorry to cause so much ruckus! :icon_biggrin: I'm very well satisfied that the EL34 will be fine in this amp.
This will be my first EL34 amp, so learning a lot of stuff.
Something else I just learned is making any drawing in ExpressPCB is a waste of time because the forum don't support that PCB file format. So I discovered I can't do nothing with my layout drawing
in converting it to another file that is compatible with anything. The only thing I found I could do is print it out and scan it. So attached is the scan of the layout.
Please understand I am trying to make this thing work in an existing chassis that already has many holes. So that's one reason it's laid out the way it is. Also I wanted to draw it to scale so I could see how everything would fit and connections would hook up. So unless I made some awful mistakes, from what I'm seeing in my layout, I think it will work. If you don't think so, let me know. Platefire
-
Sorry to cause so much ruckus! :icon_biggrin: I'm very well satisfied that the EL34 will be fine in this amp.
This will be my first EL34 amp, so learning a lot of stuff.
Something else I just learned is making any drawing in ExpressPCB is a waste of time because the forum don't support that PCB file format. So I discovered I can't do nothing with my layout drawing
in converting it to another file that is compatible with anything. The only thing I found I could do is print it out and scan it. So attached is the scan of the layout.
Please understand I am trying to make this thing work in an existing chassis that already has many holes. So that's one reason it's laid out the way it is. Also I wanted to draw it to scale so I could see how everything would fit and connections would hook up. So unless I made some awful mistakes, from what I'm seeing in my layout, I think it will work. If you don't think so, let me know. Platefire
wiring errors that stand out
- on V2, move the jumper on V2 from: pin 2 to pin 7 to: pin 1 to pin 7.
- on neg bias PS: 33K/25K pot going to 220K grid-leaks - 33K should be tied to bottom of bias pot, other end to ground - top of pot & wiper goes to 220K grid-leaks - that was my error, not yours. sorry! :embarrassed:
i updated schematics, please see attached.
- one typo - 320K plate for V2 should be 330K
--pete
EDIT: if it makes things easier for you, swap locations of 33K and 25K pot. so then bias supply to grid-leaks would be from node of 10K & 22uF & 33K to the two 220K resistors.
-
Thanks! I'm still a little confused about the bias pot hookup. Check my new revised scan to see if that works? Platefire
-
That works. May I suggest... rather than running two wires to the bias pot, just run one wire. The second wire can be a short jumper on the board.
-
no, not ready quite yet, the error on V2 is still there. please re-read schematic: connection is from V2a plate (pin1) to V2b grid (pin 7). so jumper is from pin 1 to pin 7. layout still shows pin 2 to pin 7.
other error is on V3 now:
you moved jumper on V3 - V3 jumper is pin 3 to pin 8 ( cathodes bonded).
respectfully,
--pete
-
marked up layout attached.
--pete
-
May I suggest this layout for V2. Put the 330K directly on the socket. This layout is very common and in your case will save 4 turrets on the board.
-
Yes, thanks sluckey and while we are talking about board space--the two caps 22 caps at 160V in the bias supply are almost non-existent in my searches so far. There are 22's at lot higher voltage that are also larger caps from .64" x 1.25" to .80" x 1.625".
So as you see on my board I just used symbols and didn't account for a large cap. So what I am saying is if I can't find a smaller cap to fit in a space a 100/100 would fit in, I will also need to open up the board in that area to make room. So you may of just bought me that space. Platefire
-
Wow you guys keep accumulating more mistakes on this layout! Where in the world are they coming from :dontknow:
Less Smoke, no Joke! :blob8: Thanks for Looking!
-
Yes, thanks sluckey and while we are talking about board space--the two caps 22 caps at 160V in the bias supply are almost non-existent...
http://www.mouser.com/ProductDetail/Nichicon/TVX2C220MCD/?qs=7EEPR5pZqDfnCUD2VG1N7g%3d%3d (http://www.mouser.com/ProductDetail/Nichicon/TVX2C220MCD/?qs=7EEPR5pZqDfnCUD2VG1N7g%3d%3d)
http://www.newark.com/vishay-bc-components/mal204121229e3/aluminium-electrolytic-capacitor/dp/98K6692 (http://www.newark.com/vishay-bc-components/mal204121229e3/aluminium-electrolytic-capacitor/dp/98K6692)
http://www.ebay.com/itm/like/331731305014?ul_noapp=true&chn=ps&lpid=82 (http://www.ebay.com/itm/like/331731305014?ul_noapp=true&chn=ps&lpid=82)
-
the two caps 22 caps at 160V in the bias supply are almost non-existent in my searches so far.
Why even use 22µF caps? Marshall was very fond of 10µF bias caps. Doug has 10µF @ 100V that are only .25" diameter and .5" long. I'd use those if I had to buy some.
-
Did I say "non-existent"? :BangHead: It must be a good reason DL is liking the 22/160. The 10/100 would certainly fit better in the slot. Thanks, Platefire
BTW-A fellow would have a hard time finding excuses why he couldn't do something around here :l2:
A big ol THANKS
-
must be a good reason DL is liking the 22/160
Probably for the same reason I use 25µF @ 150V. Bet he has a bin full of 'em. :wink:
http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg (http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg)
A fellow would have a hard time finding excuses why he couldn't do something around here
'cept when it comes to standby switches! :laugh:
-
platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.
the correct black and brown taps will have approx. 5 to 6 ohms resistance.
--pete
-
You could save more space and one turret if you put three turrets in a row and mounted the diode and 220K of the bias circuit like you did the input components to the EL34 grids.
-
mresistor's suggestion depicted.
--pete
-
Yes, thanks! Good idea. But DL, what did you use to manipulate my scan? Platefire
-
Yes, thanks! Good idea. But DL, what did you use to manipulate my scan? Platefire
M$ paint... :smiley:
--pete
-
> caps 22 caps at 160V in the bias supply are almost non-existent
When we all fixed ACDC table-radios all day long we bought a lot of 150-160V caps. 117V*1.414 is 165V, but rectifiers sucked, profit was tight, and 150V caps were common.
This is a lower-Voltage EL34? Then you don't need even 40V on the grids. With trim, you might want 75V caps.
But 160V for bias-supply on non-insane amplifiers suggests a big pile of leftover table-radio caps which need to be cleared-out. Gar used them like they were going out of style (which was exactly the situation).
-
platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.
the correct black and brown taps will have approx. 5 to 6 ohms resistance.
--pete
DL, I taped the two primaries that were connected/used together so I'd be sure re-use the same ones. The Ohm reading you suggested don't match mine? Reading Ohms in between the Primaries mine looks like this:
Black & Brown that was used=1.8 Ohms
Black (un-used) & Black (used)=1.6 Ohms
Black (un-used) & Brown (used)=.5 Ohms
My meter has .3 Ohms just touching the probes together.
So why is mine reading below what you said it should be??? Platefire
-
platefire: MAKE SURE you use the correct black wire on the primary. if you mistakenly use the 110V black and 120V brown you WILL FRY the PT.
the correct black and brown taps will have approx. 5 to 6 ohms resistance.
--pete
DL, I taped the two primaries that were connected/used together so I'd be sure re-use the same ones. The Ohm reading you suggested don't match mine? Reading Ohms in between the Primaries mine looks like this:
Black & Brown that was used=1.8 Ohms
Black (un-used) & Black (used)=1.6 Ohms
Black (un-used) & Brown (used)=.5 Ohms
My meter has .3 Ohms just touching the probes together.
So why is mine reading below what you said it should be??? Platefire
cool! just concerned.
my mistake, i measure 1.6 ohms on the 120V winding on the PT i have.
--pete
-
OK, goood! Ready to Roll>>>>>>>>>>
Thanks for letting me know the danger of smoking a PT, I'll be super careful. Platefire
-
mresistor's suggestion depicted.
--pete
Hey DL that was way cool, I wish I had half the talent you and some others here have with the software. If the caps are small enough one could delete two more turrets on the 22 uf caps to the east the bias diode. one could delete the middle turrets, and fit the caps to the real estatate. :-)
-
I re-arranged my board layout drawing to include most of your suggestions. The length of the board has been reduced from 13" to 12". I could of reduced it another 1/2" probably but didn't see the need. 12 is a good round number.
DL, on the my layout scan you manipulated to change the bias dropping resistor and diode---haven't you got the diode facing the wrong way?
I called myself checking everything to see if I got everything connected back up right, but you know how that goes! I welcome you to check me out :help: Platefire
-
100uF? for bias supply filters? seems like overkill but at least the hum source won't be the bias supply! :icon_biggrin:
22uF is borderline excessive, 47uF is probably prodigal.
--pete
-
haven't you got the diode facing the wrong way?
The bias diode is drawn correctly in that latest layout pic.
-
Yeah, guess 100uF is kind of overkill :dontknow: Guess I was looking at size more than value.
I did go through my inventory. Found some NOS Tantalex 13/150 and some Radio Shack 22/50's.So out of that I guess the 13/150 is the best fit. I've even got one 50watt Marshall 1987 schematic that even shows 8uF. Thanks for all you recommendations/improvements that got incorporated into the layout. Platefire
-
looking pretty awesome ...
-
Thanks mresistor
Kind of rag tagging existing parts together to make a project. Without all Dummyload and sluckey's help, it would have never even got off the ground. I've been having these Hammond PR-40 parts for years and thought they were useless to me. I will try to make it nice as possible.
Haven't decided rather I will leave it as an exposed chassis with all the tubes hanging out or enclose it in a head cab. It's going to be a little top heavy with the big transformers top mounted---a cab with a well placed handle of handles might help that. I kind of think of it as a hot rod amp, so maybe it would be better leaving everything exposed except a bottom plate to cover the circuit and to mount feet on. Something to ponder on in 2016. Platefire
BTW-Here is the latest rendition of the Layout. Thinking of calling it "Plexi 48 Hot Shot"---referring to a plexi with hot switch.
-
You could lose 1 more turret. Put the .1 cap on a 45 degree angle up to the 10K R and bring the 100K R to that junction too. and move the turret to the right at the bottom of the 100K R. Don't forget to move the jumper wire up to the 10K/100K/.1 junction. :icon_biggrin:
-
Willabe
With all the recommendations to rearrange to save turret lugs, I went back and checked the current price thinking they must of severely went up in price :l2: (15 cents each). With your recommendation I can see where I could also re-arrange the mounting of the .022 cap above that location and shift all the components east of that location, further west another 3/8" spacing forward therefore reducing the length of the board to 11 5/8" long.
However I might wait for any more recommendations to come in before I shift any more components
so I can do it it one final sweep. In other words, I've got the "layout correction Blues" :sad2: Thanks, Platefire
-
My layout designs usually go through several minor revisions until I'm satisfied. I don't rush this phase.
-
Yeah, I need to take it easy. I'm my own worst driver! Relax and enjoy the ride. Take time to get it right. :thumbsup: Platefire
-
Revised Layout again. Willabe's suggestions have been incorporated. The board in now 3/8" shorter from 12" to 11 5/8" long. It should be getting close to being all it can be :laugh:
Also got attached OT from ClassicTone coming. Platefire
-
Got the OT in today. This looks like the way I need to position the transformers/choke. If you see any problems, let me know. The rectifier is 1" from PT. Platefire
-
I positioned my transformers on my Single-ChanDR very similarly and the PT is also very close to the rectifier and haven't had a problem at all. Also it should be noted that on many of the old Hammond PS chassis the PT is in very close proximity to it's valve rectifier and they work fine.
-
Thanks mresistor
I also have a Pignose G40V and everything is really crammed up in close proximity, and it seems to work OK. I pretty bad about missing stuff, so it's nice to have someone look over your shoulder. Thanks, Platefire
-
my thoughts: the choke is carrying power load of the amp. it it will have stronger flux lines, so suggest rotating choke and OT 90 deg. my concerns likely unwarranted so take with a grain of salt, so to speak. just thinking out loud...
--pete
-
DL, I thought the choke needed to be 90 degrees out from the PT. If I rotate the choke and OT 90 like you said, that would put the bells all facing the same direction. Is that what you was talking about??
Now if I rotated just the OT 90 degrees from it's present position, that would put all three 90 degrees out from each other. Which one? just checking :icon_biggrin: Thanks, Platefire
-
If I rotate the choke and OT 90 like you said, that would put the bells all facing the same direction....
yes.
--pete
-
OK, Like this!
-
OK, Like this!
yessir, that's what i was thinking.
--pete
-
Looks like a bunch of soldiers standing at attention to me :l2:
-
i built this on the dual SE marshall breadboard. lost interest and was about to tear it down, so i grafted in the hammond PS and one of doug's 50W 4K:2/4/8 bassman OT - p/n 018343. sounds really nice - couldn't kick in the pants as it was late. a friend came over to play it and likes it's clean tone. it's fairly loud as well.
with SSR, B+ surges to 540V for about 5-6 seconds at turn on & don't care: these are JJ caps for experimenting on the breadboard. if i were to build it, i'd use MIEC 47uF 600V caps.
schematic with telemetry attached.
--pete
-
Interesting! Two chokes? that's a new one on me. So on the clean setting that you was liking, what was your two volumes set at?
I've never installed a relay before but I think I might look into that for the possibility/difficulty to make my hot Switch, foot switchable. Not sure just a consideration. May aught to build it with just a DPDT first to see if I like it first. On the one amp I now have with a hot switch, I tend leave the hot switch on all the time and set the volumes so i can go from clean to sting with my guitar volume. Platefire
-
single coils on strat. preamp at about 1/4 - master at about 1/2. if you run PS with SSR use 600V electrolytics.
http://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1587 (http://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1587)
--pete
-
Sooooo-------if I use SSR and 600V caps, that means I can have a standby switch, right? Platefire
-
ju don need no steenking standbai.
in theory, yes.
--pete
-
DL, since you shed new light on how the the Hammond PT/Choke/SSR behaves with the 2204, I decided to do my version of my layout with SSR. Please check um out!! :evil5: Thanks, Platefire
-
flip the 220K grid leak resistors for the power tubes and save a turret and some wire.
what you've laid out will work, however, i'd like propose a couple of suggestions:
a) if you flip the preamp power supply caps (C, D, & E) you could run the power rails on the tube side of the turret board. that keeps power away from the pots and ground rail mixed with the signal lines. if you flip the anode resistors orientation, that would help in that respect. also, you'd run the power leads under the turret board.
b) the bias supply has high volt AC supply mixed in with DC runs, suggest that it be moved to the end of the board - closest to the A & B supply rails and share the same ground. run the output of the bias supply along the ground side of the board or under the board to the grid leak resistors of the power tubes.
thoughts? other ideas? comments?
--pete
-
Thanks! Think I will think about this a while. Platefire
-
Hay I'm back! I agree with all the suggestions you made, just had to take a short break and refresh :brushteeth:
I am working on a new plan and will post it soon as it's done. Thanks, Platefire
-
DL, this is my rendition of what I think you recommended do. Check it out and see if I'm even in the Ball Park :dontknow: Thanks, Platefire
-
I just noticed that the PI B+ and coupling caps on the eyelet board are wrong. :w2:
Coupling caps are being fed after the PI plate R's. So the AC signal from the PI that goes to the power tubes has to go through the PI plate R's.
-
what willabe said + the bias feed is AC not DC as there is only positive there. you need need the negative half of the sine there.
please see attached for clarification. :-)
--pete
-
Yep, I did the same thing on the V1 plates/caps too. :l2: Think I will re-title this amp "Twilight Zone". I can tell it's still pretty poor layout looking at you guys boards but here is the corrected copy. Maybe in all it's poorness it will still work. Thanks for your great tolerant patient inspections! :worthy1: Platefire
BTW--I thing scooting the board further east about 1" toward the PT will also help the hookup runs.
-
BTW--I thing scooting the board further east about 1" toward the PT will also help the hookup runs.
Yep, agree. :icon_biggrin:
Besides you don't want the west end of the board touching the west end of the chassis.
-
BTW--I thing scooting the board further east about 1" toward the PT will also help the hookup runs.
Ah, the beauty of Visio and full scale components! There's no guessing if it will fit or how the wiring will look. It should look just like the drawing.
Not saying you must go out and buy Visio for just one layout. But if you have Visio and are not using it, you are missing a lot.
-
I didn't know what Visio is, so I did a google search on it. I definitely don't have it already. I really do miss a good drawing program because in my job I had the best with every tool you could imagine to accomplish what ever you needed. In ExpressPCB/Sch you really have to be creative to accomplish what you need. So I'm assuming you have Visio? Platefire
BTW-I'm looking at a CAD Clone free download "Draftsight". Would like something I could do
electrical, architectural and mechanical with.
http://www.3ds.com/products-services/draftsight-cad-software/free-download/ (http://www.3ds.com/products-services/draftsight-cad-software/free-download/)
-
curious as to what are the chassis and board dimensions are? the big E-caps don't seem to be to scale.
--pete
-
I didn't know what Visio is, so I did a google search on it. I definitely don't have it already. I really do miss a good drawing program because in my job I had the best with every tool you could imagine to accomplish what ever you needed. In ExpressPCB/Sch you really have to be creative to accomplish what you need. So I'm assuming you have Visio? Platefire
BTW-I'm looking at a CAD Clone free download "Draftsight". Would like something I could do
electrical, architectural and mechanical with.
http://www.3ds.com/products-services/draftsight-cad-software/free-download/ (http://www.3ds.com/products-services/draftsight-cad-software/free-download/)
draftsight works and is better than what you have now. it's not as versatile as visio, but far better than express sch for layouts.
you should be able to buy visio 2010 download + activation key for under $200. be careful buying SW off ebay.
--pete
-
Well on ExpressPCB, I have it set to inches and not mm. So each square grid is a square 1/10 th of an inch. So those 50/600 E caps are 11/16"(.6875)x 1 7/8"(1.875). 1/16"=.0625 and 1/10th of an inch divided by .0625=1.6 sixteenths in every .1(1/10") cube or .8 Eight inch in every cube.
So 11/16"divided 1.6 Sixteenth per block= 6.75 Blocks in diameter.
and 1 7/8" long divided by .8 Eighth inch per block=18.75 Blocks in length.
That's is how I scaled it and when I drew it I thought it too large also, but when I checked my dimensions or blocks, it was correct and when you compare it to the 3 1/4" board it does look proportional to that.
If you find any flaws in my measuring techniques, let me know. The outside dimensions of the chassis is 8 1/4" x 22"(8 1/8"x21" inside). The board is 13 7/8" long. The end plates of the chassis that the handles go through is 1/2" aluminum---weird/heavy! Platefire
BTW--also the X(horizontal) and Y(vertical) Grid coordinates help located everything from point of beginning, upper left hand corner of turret board.
-
ju don need no steenking standbai.
--pete
I used to think that a standby switch was important for tube amps. I mean most of them have one, right?
We need to warm them tubes up before throwing them into action, I've heard people say. :dontknow:
Then I spent the time to read the PS section on Merlin's website. Major eye opener. :huh:
Now it seems to me the downsides of using a standby switch far outweighs the positives.
With a tube rectifier our B+ gradually climbs to operating voltage as the tube warms up.
The biggest drawback is one I had never heard about before. Decreased tube life.
Heating the tubes without voltage applied for extended periods creates a chemical reaction and a film to build up on the elements.
Once that film develops there is no way to remove it. Leading to a significantly shorter useable tube life.
I want my expensive tubes to live long and prosper. \\// :l2:
-
I wonder about Marshall 2204 style standby?? they cut PT secondary ACV Reds to rectifier and allow the heater ACV to keep the heaters going. never tried that method before! :w2:
I hadn't planned to put one in this one, but thanks for reminding me. :bravo1: Platefire
-
Well on ExpressPCB, I have it set to inches and not mm. So each square grid is a square 1/10 th of an inch. So those 50/600 E caps are 11/16"(.6875)x 1 7/8"(1.875). 1/16"=.0625 and 1/10th of an inch divided by .0625=1.6 sixteenths in every .1(1/10") cube or .8 Eight inch in every cube.
So 11/16"divided 1.6 Sixteenth per block= 6.75 Blocks in diameter.
and 1 7/8" long divided by .8 Eighth inch per block=18.75 Blocks in length.
I think your making it much harder than it needs to be. :w2:
I set the 'Display grid' at .0625 (1/16") and the 'snap to grid' to .03125 (1/32"). So I can snap a line or part in between the 1/16" grid.
I measure every part I use and make it to scale, then name/store it. So everything is to scale in my drawings.
This way I can print out any templets I need to make an eyelet/turret board or for a transformer placement/drilling templet.
I also make little rulers that are a single line with cross hatch marks on the 1/4" and are numbered on the 1" mark. I save these and put them on the drawing I'm working on when needed.
To be able to save them as a part you have to put a dot on it or it wont save. And you can flip them/rotate them left/right and up/down, so you only need to make 1 of each length.
-
I wonder about Marshall 2204 style standby?? they cut PT secondary ACV Reds to rectifier and allow the heater ACV to keep the heaters going. never tried that method before! :w2:
I hadn't planned to put one in this one, but thanks for reminding me. :bravo1: Platefire
Still heating your expensive tubes = chemical reaction = premature tube death. :sad2:
-
Willabe
First of all, this is the first layout drawing I've tried since I retired and had to give up all my expensive drafting equipment. Second I made a big mistake when I started in ExpressPCB instead of ExpressSch---because I didn't find out until I tired to post it, Doug's forum don't support ExpressPCB files, only Sch files. So I won't try that again in PCB :BangHead:
But Man Thanks! for the tips on setting the grid. I tired it and works great. You layout drawing looks fine. Drawing and saving parts also sounds good, because once you draw them to scale, you can use them from now on. Your right, I was making it harder than it needs to be.
Also I'm interested in what you said about printing out board templates. Like how do you print them out full scale? and also if board is longer than 11"(8 1/2 x 11 sheet), how would you print it out like mine 13 7/8"? Platefire
-
Also I'm interested in what you said about printing out board templates. Like how do you print them out full scale? and also if board is longer than 11"(8 1/2 x 11 sheet), how would you print it out like mine 13 7/8"?
You can use legal size for up to 8 1/2" x 14". But if it's longer than that then;
You have to make a 2nd drawing of just the board, print it, cut the 2 parts of the board out and then tape them together, but it works fine. Just a little more work.
Once the drawing is finished, you highlight the full eyelet/turret board, then copy, then past it on a new sheet. Size the new sheet to what ever size paper your going to print on, 8 1/2" x 11" or 8 1/2" x 14". Print full size/full scale.
Then you find a place where you want to break it in two. I run a line from top to bottom where I want to break it and put 3 small lines going left to right across so I can line them up after it's printed and the 2 pieces cut out.
Play with it a few times and you'll get it right. :icon_biggrin:
-
was thinking something like the attached. probably would be better if the B+ nodes D & E caps were centered between the V1 & V2 components: it's late and that's about it for me tonight.
i have the visio file for this layout and IF you like it, then perhaps doug might be willing to fab the board for you on his CNC? couldn't hurt to ask unless he has a huge cyber club.
--pete
-
Wow! That is pretty amazing. I ran some hard copies so I could study it awhile. Thanks, Platefire
-
latest rev: rev2. i like this one mo bettah.
i included patterns for boards with 1/8" eyelets and hoffman 3/32" turrets.
--pete
-
Well all I can say is that is about an efficient board design for this particular amp situation as you can get. That's got to be it! I'm really impressed with Visio too, it looks like the real thing in every detail. I personally like turrets over eyelets but you got both covered. I assuming you could also do a dandy chassis layout with Visio too. Thanks for all the hard work to put that together. I'm learning a lot about board layout. I thought I knew a little, but I might be mistaken(as Billy G once said)! It really is an art to include all the best electrical practices and symmetry. It looks like you got that pretty well nailed.
What it Doug's CNC---computer Bla Bla? I usually enjoy making my own boards, but if it wasn't an arm and leg, might be alright!
Got a question on a couple of value caps on revision 2. On V1 cathode cap you have a 25uf instead of a .68 and also to V3 -2 you have .0022 and instead of .022. Don't know if your recommending a change or it's a mistake?
Thanks much! This thing is going in the right direction. Platefire
-
Got a question on a couple of value caps on revision 2. On V1 cathode cap you have a 25uf instead of a .68 and also to V3 -2 you have .0022 and instead of .022. Don't know if your recommending a change or it's a mistake?
Thanks much! This thing is going in the right direction. Platefire
glad you like it: i'll fix those errors shortly. you can create the wiring diagram and any assembly diagrams in visio - several folks here and self do as well.
i created this (http://el34world.com/Forum/index.php?action=dlattach;topic=17300.0;attach=44262) amp completely in visio: it went from a concept experimenting with pentodes to a working model.
--pete
EDIT: corrections attached. please review and check wiring. :icon_biggrin:
-
Thanks! Believe it or not, I'm not sleeping! I'm going over the final board layout and am accumulating a few questions that might not amount to a hill of beans but maybe need to be ask before we proclaim this the final plan. Maybe some of it due to my unfamiliarity with Marshall. When I get it all together, I'll post. Platefire
-
Ok, here goes so this may be long. My only experience with a Marshall was a 80's Plexi that I repaired. So my concentration was mostly the repair, but I do recall liking it, what little I played on it. So Marshalls are a blank canvis with me but I know the original sprang from a 5F6A Bassman and developed from there. So I can see a lot of 5F6A in this amp. So I see some of the major differences is in the preamp, power tubes and seems more filtering of power rail. So my desire on this project is to sample the Marshall animal a little bit. So some of my thoughts on the amp may be based on assumptions and not fact. So I would like to be sure I'm truly understanding what I'm building.
So I had to select a 50 watt(48) circuit for this project so the 50Watt Master Volume 2204 was what I selected(schematic attached). My thought was to have a low gain channel for mostly cleaner stuff and have the hot switch to bring in the other gain stage to make it really distort or either leave the hot switch on all the time with the MV turned down and preamp Vol up and just use my guitar volume to go from clean to crunch. So my major change to the 2204 circuit was to do away with one channel and bring the other gain stage in with Doug's hot switch as needed. So based on all this assumption, this is my questions:
1-Inputs & Channels on the attached stock 2204.
a- I assume the "low" and "high" inputs/channels on this amp are for low & high gain?? but not sure. I know on vintage Fenders the high was like for single coils and low for humbuckers because clean was the goal and they sure didn't want their amps to distort. I know Marshalls where trying attain more gain---so their intention for low & high may be completely different. So the low input has a cathode 820R/330cap and the high has a cathode 2.7K/.68 cap on attached example. My amp inital clean channel has a cathode 2.2K/.68cap which is more in line with the "High" channel. I see on Doug's hot switch schematic, he has the cathode 2.2K/.68 as the inital Plexi channel. I think seeing Doug's V1a cathode set up is why I used it on mine! This is a little confusing to me. Would those values be right for what I'm trying to do?
b-The output of the plates on V1 has a .002 coupling cap on the high channel and .02 on the low channel. I've got the .02 on mine with the high channel style cathode set up. So I know the higher value is less bright---so I think that the .02 would be better because I really don't want a overly bright sound or am I tracken right?
c-I also see the 100K resistors after the coupling caps. I am assuming that these are to help separate the signals of each channel going into the volume pot and since I only have one channel is not required for mine??? Anyway I don't have the two 100K's in my amp and haven't tried to include them because of the previous reasoning. Is my reasoning good?
2-Tone Stack:
a-Just wondering? On your board layout you have the second .022 labeled to bass 2 term. Since the bass 2 term connects to treble 3 term, couldn't you just run that one you got labeled bass 2 to treble 3 since there will be a wire run from Treble 2 to Bass 2??? That would be a shorter run if legal:>)
b-On the bass pot on the attached 2204 schematic there is an arrow through it, which I never knew exactly what that means? So on my schematic you made a correction where you disconnected Treble 3 connection to Bass 1 connection and connected Treble 3 to Bass 2 and left a no/connection on Bass 1. So is that what that arrow through pot means--the correction you made?
I have checked your layout and everything looks good to me. If any of the questions I ask don't cause any major repercussions, we should be good to go. Thanks Much! Platefire
-
there is an error. input from MV-2 to LTPI .022 coupling cap - the wire from the top of the 1M to .022 needs to go the bottom of the .022 cap not the top of the .022 cap. feed from pin 2 of MV goes to top of .022 cap
- i'll fix it tonight when i get home.
--pete
-
Yeah I missed that, glad you caught it, not too bad, just more one wire. Also what happen to the 47p between the grids right after the PI? Platefire
-
corrections. please see attached.
- added 47pF cap.
- corrected LTPI input wiring.
- power to V1 plate load resistors.
- connection points to V1 plates on ckt. bd.
--pete
-
rev. 3 - third time's the charm, eh? :p
- moved the node D cap closer to V2. cleaner layout. also, V3 wiring is more tidy.
- moved the .1uF presence pot cap that's connected from wiper to GND off board to pot.
--pete
-
Good, Thanks! Was able to print it out using poster setting and got a 3 page 8 1/2 x 11 mosaic full scale that I can scotch tape together and make a drilling template. I notice your board is 3" wide and all I've got from Doug is 3 1/4" wide--can he make it 3" wide? Platefire
-
Good, Thanks! Was able to print it out using poster setting and got a 3 page 8 1/2 x 11 mosaic full scale that I can scotch tape together and make a drilling template. I notice your board is 3" wide and all I've got from Doug is 3 1/4" wide--can he make it 3" wide? Platefire
i just checked the catalog: doug's boards are 3-1/8" wide & he won't cut any other width. i used 3" since that made dimensioning easier for me. i revised the drawings (rev 3a) and made the board 3-1/8" - 3.130" is close enough! :-) rev 3a drawings attached.
if you have a kinko's nearby, they can print 11"x17" for you. down the road you can get an A2 size printer fairly inexpensive: such as this one. (http://www.staples.com/HP-Officejet-7110-Wide-Format-ePrinter/product_142140?cid=PS:GooglePLAs:142140&ci_src=17588969&ci_sku=142140&KPID=142140&gclid=Cj0KEQiA5oy1BRDQh6Wd572hsfkBEiQAfdTPCr4IsKudzXzwHOjALxWZ0kK2BPkTqwOVNYoy90cO8_saAtsn8P8HAQ)
--pete
-
Just when I think it can't get any better, it gets better! I'm not going to comit that this is the final version but I went ahead and made a template. I can drill with this! :laugh:
Think things are firming up to order some more parts. :evil5:
Thanks for all the great help! Here is a pix of my template. Platefire
-
Hey now, that'll work. Very nice. :icon_biggrin:
-
you're most welcome. hope it works well.
--pete
-
In the process of going through my existing inventory to see what I got that I can use and what I need to order.
IMH0--if the schematic calls for an .022 coupling caps and you got some .025 or calls for a .1 and you got a .15----to me that's close enough and is not going to make that much difference other than leaning darker than brighter and in my case a hair darker is good! Is that copasetic?
-
yes
-
Thanks for seconding me, amendment passes! :evil5:
-
I've got some diodes that looks similar to Doug's "B"1N4001 is size but all I can read on it is "V2N"?
I can't find anything on the net that identifies :dontknow: Trying to determine if this will work for my bias circuit. Platefire
-
I don't know about your diodes, but I got 100 1N4007s from China for $.99 including shipping.
I think one of those might be OK in the bias circuit. :dontknow:
I don't know how those commies manage to do that for $.99? :w2:
-
Well at 25 cents each, guess I'll just throw one in my order to Doug to be sure.
Also on EL34's, if your wanting to lean more to a Marshall Crunchy breakup sound than a clean sound--what EL34 is best budget minded. I've read the the EH tends to be better than a JJ for the Marshall sound. Platefire
-
I've got some diodes that looks similar to Doug's "B"1N4001 is size but all I can read on it is "V2N"?
I can't find anything on the net that identifies
Throw them away if you cannot determine the ratings. They may not even be rectifier diodes! There is a wide range of diode types and ratings that all use that same body style. Could even be a trigger diode or diac.
Throw them away!
-
OK, I've been busy with other stuff. Trying to pick up where I left off. I'm wanting to do cutting and drilling for cover plate and drilling for transformer holes. We last talked about transformer arrangement in post #115 & 116. So in reference to that I have took attached pics with that in mind, with a couple of exceptions. Since we are now using SS rectification, I arranged the cover plate to cover the two tube rectifier holes. Had to put the choke right up against the cover plate edge that was about 1 3/4" from the PT, so I also left a 1 3/4" space between choke & OT. May be a little to spread out now? So whutadouthink? Platefire
-
looks good. :-)
--pete
-
OK, Thanks DL! I will go with that. Platefire
-
A little progress. Having to prep this old chassis to bring it around. Not going to concentrate on building the circuit until I see everything is in order on the chassis for mounting and fitting everything in--once that's clear I'll proceed with electronics. This chassis looks so rough I think it would classify in the Steam Punk category:>) This chassis was given to me when an amp building friend cleaned out his surplus junk and gave it to me. He sometimes post here as Wooley. This is an explanation of attached pictures:
1 & 2-Where the input jack needed to go was a large hole, too large for an input jack. I built an aluminum cover plate to cover it and drilled a new input jack hole. Had to scoot it over to the left as much as possible to make room for the DPDT midi switch(hot shot) between the input and pre vol. A outside and inside pix.
3-Marked chassis cover plate for mounting that huge PT. Will be using 1/4" mounting bolts on that. The sharpie marks are where the 1/4" bolts go and the large holes is 5/8" Dia to match PT wiring holes that will have grommets.
4-The small rectangle marking pix is where the IEC receptacle will go. I had to flip it vertical because of lack of space between the heavy 1/2" thick alum chassis end plate and the fuse holder.
Even though I'm taking my good time on this, I am looking very much forward to one day soon firing it up. I think once I get the chassis preped and ready it will go faster. Platefire
-
ahhh progress!!
my notes so far: with cascaded V1 (aka the 2204) my breadboard amp is typical JCM800 sounding even with this output stage. it breaks up about the same. IMO, overall it sounds better with the bassman/JTM/plexi preamp.
--pete
-
pete
Yeah, I'm not familiar with what a typical JCM800 or a JTM Plexi sounds like. You have to realize, I've never played over a Marshall before. That's what I'm wanting to discover! So when you you say it sounds better, I'm wondering in what way?? When you say it sounds better with the bassman/JTM/Plexi preamp are you referring to the particular circuit attached or something else??? Platefire
-
Well pete
Guess it's no big deal. If I don't like the way the 2204 pramp sounds, it would be easy enough I think to change it to the JTM bassman preamp and try that. Guess I'll go with the established plan first and go from there. Tweak it Babe, Tweak it! Thanks, Platefire
BTW-since you are very familiar with the PR-40 power supply, I will be using 600V filter caps, do you think it would be safe to install a standby switch. The hole is already there. If I don't use it, I'll have to plug it:>)
-
do you think it would be safe to install a standby switch.
sure.
--pete
-
fairly concise history on the many models of marshalls and schematics in link below:
http://www.drtube.com/en/library/schematics/69-marshall-schemas (http://www.drtube.com/en/library/schematics/69-marshall-schemas)
the 2204 (50W) and 2203 (100W) later become the JCM800 series, are a completely different animals from JTM45/50 models. V1 is cascaded and a master volume added after the tone stack. amp has 2 inputs: high and low - the low input bypasses the 1st gain stage. these are the most dominant marshalls from 1975 through the 80's.
--pete
-
Yeah, since I started building this Marshall type circuit I'm learning a lot about Marshall models numbers/names. Also have read some history. Pretty interesting. Guess I'm wanting to taste a little Marshall glory in a little less wattage. I'll have to wait until the wife is gone to really give it the real test :l2: when it's finished.
I got a local amping buddy that lives about 40 miles away and we talk several times a week. He just bought a Germino JTM 100 clone$$$$ I will attach their link but they are very meticulous about re-creating the amp electronically and cosmetically in every detail as they were built in 1966. I will be going by there soon and playing through it a bit. He just bought a Freeman matching 2-12 cab with vintage 30's in it and he also has a 4-12 Marshall cab but not matching. Here is the link:
http://www.germinoamplification.com/# (http://www.germinoamplification.com/#)!monterey-100/c18r5
Thanks, Platefire
-
Those Germino Marshall clones are said to be killer.
-
Chassis prep continued: :icon_biggrin:
finished drilling the cover plate for the PT wiring holes to chassis and tested inserting the grommets. Will now have to take them back out and finish the steel plate or it will rust pretty quick. IEC holes looks a little rough. Wasn't easy cutting it out around the existing hole with the tools I had on hand. Once the IEC socket is installed the roughness will be covered. Also cut another pot hole for the presence control.
Still need to drill mounting holes for choke and OT. Try to find some vinyl plugs to put in existing un-needed holes. After that the chassis should be fully prepped and ready for board/Electronics. Platefire
-
Here is the Hot Shot 48 in it's former Glory done by Wooley in about 2002-2003 in that period when it was a Marshall 2203 circuit. According to him, the chassis came from Doug, he added the handles.
Edit: Also added a board picture of the original 2203 provided by Wooley. Hard act to follow!
-
nice!
--pete
-
Sometimes this stuff plays tricks on your mind :w2:
on this Classic Tone OT primary's are blue/white/red
now I'm sure that the red is the B+ and blue and white to plates----just say Yeah!
For some reason white seems like a strange color to plates--just making sure. Transformer pdf dwg is attached. Platefire
-
now I'm sure that the red is the B+ and blue and white to plates----just say Yeah!
WRONG! You better look at your wiring diagram.
-
So you are saying center tap is B+ regardless of color(white).
Why they want to go messing with old standards?
-
So you are saying center tap is B+ regardless of color(white).
yes
Who ever accused those Brits of having a sense of standards? :icon_biggrin:
-
Thanks, Sluckey
Well I guess my OT Classic Tone is made in the USA but they had a color code comparison to the old Drake
OT I found in lower left hand corner of OT drawing as follows:
PRIMARY LEAD COLORS:
DRAKE 40-18025
WHT BLU
BRN WHT
RED RED
every OT I ever installed to date(that I can remember), Red has been primary B+ but on the old Drake Brown was B+. So OK OT color code class is done for the day---glad I didn't hook that red up to B+ :l2:
Platefire
-
> center tap is B+ regardless of color
CENTER tap. Push-pull. Think of a see-saw. If you move the pivot to the left end, and put the kids center and right end, it don't see-saw too good.
> Why they want to go messing with old standards?
There was no reason for the UK and US to have common standards until WWII. Not really a lot of cross-ocean mechanical or electrical trade. Different bolt threads. Different ways of specifying bolt tolerances. Different way of drawing blueprints! Some of this was cleared-up, enough to make guns and tanks. There was some feeling there should be more commonality. But UK cars and cycles used Whitworth bolts into the 1970s-- why change?
You know a US RETMA/ASA color code.
Apparently UK transformer makers knew another code.
There was little cross-Atlantic transformer trade until the Williamson, mid-1950s. Even then, the cost of shipping large iron over the water fostered many USA clones. Also a true Williamson, or the UL variant, has so many leads that the builder really has to Be Careful. UK color codes may have been rare in the US until the Marshalls started coming in large numbers.
If you are restoring a fine old UK Marshall, you "HAVE TO HAVE" the original genuine wire colors. ClassicTone does it correct per the originals.
> glad I didn't hook that red up to B+
Interestingly, it would not blow up. But it would be way-way down on power. Like the see-saw with the pivot at one end instead of center.
-
Thanks PRR for the history on this. I guess we are a little more Globalized on standards now days. Since I've been working on this Marshall Clone, I have been reading up on Marshall history. When Marshall first started importing amps to the states they ran into issues on what power tubes to run in them. I think the one shipped to Canada had one type power tube and the USA had another and the ones in England another.
I still shy away from metric but use it when I haven't got a choice. I have to use an American vs Metric comparison chart. Platefire
-
Yeaa! :blob10: Finally got the old chassis fully prepped for all the holes with cover plates and plugs for existing un-needed holes. I had truly forgot how much work is in re-purposing an old chassis like this. But finding the old Hammond transformers and the Hoffman chassis is what got me started in the direction of a new/old project. So I looking forward to shifting gears and to start on the board and electronics.
One question???? I got my hole for my bias pot centered about 1 1/4" away from the center of my speaker output jack. Since I've never needed to put these two functions that close before, just wondering it there could be any conflict there? Platefire
-
I got my hole for my bias pot centered about 1 1/4" away from the center of my speaker output jack.
That's OK.
-
OK, Good! Thanks Sluckey
-
Had quiet a break from this project. Ordered the 6-50uF/600 caps today and trying to re-remember where I left off. The chassis is pretty much prepped now(I think?), so I can start concentrating on the inners. Platefire
-
The bias circuit runs low negative voltage with very low current that doesn't fluctuate that much.
That circuit shouldn't be very susceptible to bleed over signals because of that.
High voltage wires with big fluctuations of current and voltage are ones to give extra space to.
OT primary wires for example.
-
I think next step may be drill the board and add turrets. I'm pretty mindful of giving high voltage DC their own space as much as possible. The only thing is I'm starting to second guess my circuit design with one of the channels preamp becoming a hot switch. I only wanted one input jack, so I'm supposing that is the best way to go. Just need to be sure I've selected the best 2204 channel for clean that will be normally on all the time because I'm mostly a clean player and the other best voiced for OD combination with the clean channel. Dummy Load seemed to approve of the design and very much assisted in the layout and board layout. So not being a Marshall specialist, I'm feeling my way!😉Platefire
-
So you are saying center tap is B+ regardless of color(white).
Why they want to go messing with old standards?
Plate, the colours are different with Drake OT's and Heybour's copies of the Drake Transformers. Since the size of the 50 Watt version they made is so close to the 100 watt, that is the only way I can tell them apart without figuring the winding ratio.
-
Been a long time since I looked at my ClassicTone OT. In Gulf Shores Alabama right now for two of my Grandaughters Summer Camp Cheer Leader Competition-----push it----push it---know what I mean? Platefire
-
Back Home now. Referring to Ed's post #193, I think this has been discussed previously on this post but here is the OT I got for this project. As shown primary ct is white and plate leads are blue and red. In the lower left hand corner of drawing it does have a primary lead color code comparison of Drake to ClassicTone, the Drake ct was brown as compared to CT white ct. Platefire
-
Got my 50/600V filter caps and my 25K L locking bias pot in. I think that's it on parts---I just need to go to work. Where did i put that drill press?
-
DummyLoad, I sent you a PM regarding last board layout you provided. Trying to get started back on the right foot! Platefire
-
Dummyload has not been on the forum since May 11. Hope he's OK?
-
That sounds very unusual for him, I hope he's OK too. Platefire
-
What's your question. Maybe someone else can answer. I've got the latest layout revision but I don't know which schematic is your final version. Can you point to the correct schematic?
-
I've been reading old post trying to get up to speed. In the last of Jan 2016 we were decided we could go from tube rectification to diode if we went to 600V caps. So we did that but that didn't get revised on the schematic. Attached is the most update schematic I have still using two 5U4 rectifiers. I need to fix that.
At about that time DummyLoad started working on the board layout plan to make it more efficent. He started using his own drawing program to produce these layouts. So if you follow the post he went through several revisions of the board layout until the last on post #155 23 Jan 16. The pdf file of that is attached.
My questions were this:
1-It appears to be a obvious mistake on his last layout on the B+ to the first filter cap shown "To diode board" should be from "From Choke". The choke would be between diode board and first filter cap.
2-In the earlier versions of his board layout drawing specifically at post #147 20 Jan 16, he had a the ground wire going under board with dotted lines to the preamp section of the board but on the post #155 latest version he went back above board with most of the ground----------so I was just wondering about his reasoning for doing that? I kind of liked it below board where all those signal wires cross.
3-Last but not least----in sizing up my drilled board with the existing Hammond Choke I found the red lead to board is about 1" short to reach the first filter cap turret. My plan was to install another turret on the board that the red lead will reach and attached it to that and run good heavy wire from choke turret to filter cap turret to make up the difference. It's either that or extend the choke lead with a soldered in/shrink wrap wire extension. Which way is best?
That's about it. Getting ready to install my turrets on the board and just need to drill any extra turret holes if need be first!
Again I hope DummyLoad is OK, got me wondering? Platefire
-
1. Yes, it's a mistake. But you know that so it's not an issue, right?
2. Only Pete knows his reasoning. I would put all the ground jumpers on top.
3. Either way works equally well. I'd just make the wire longer. Don't you have a small wire stretcher?
-
Regarding #3--Is a small wire stretcher like going Snipe hunting and sky hooks?
-
Hi Plate,
Skyhooks are a real thing, we have them in Australia.
https://www.youtube.com/watch?v=5nvth-kGtQ8 (https://www.youtube.com/watch?v=5nvth-kGtQ8)
https://www.youtube.com/watch?v=3eqmW8lqiEc (https://www.youtube.com/watch?v=3eqmW8lqiEc)
-
> Skyhooks are a real thing, we have them in Australia.
Skyhooks' "Ego..." was a big hit in my crowd. Still have the 33-1/3 vinyl. Rather let-down to discover it never charted in the US.
I have a large wire-stretcher; rather a rope-stretcher, a half-ton comealong. Makes nylon rope considerable longer than you'd think. Probably over-kill for chassis wiring.
-
Never heard of the Skyhooks until now. At least if I get sent to get a skyhook, I'll know what to look for now! Still looking for them small wire stretchers!
-
> Dummyload has not been on the forum since May 11. Hope he's OK?
Look in Pete's "Dummyload" profile, there is a web-site. At that site there are email contacts for Richard and Pete. I got a response back in hours; he's "doing well" but has not had time for the forum.
-
Good and Thanks for checking PRR, Glad he's OK. He went the extra mile in helping me with this amp, so I'm very appreciative. I need to reciprocate and finish the job. Platefire
-
He has given me excellent guidance and specific modifications for a Bogen K10 PA. :worthy1:
I too am glad to hear he is well.
Most of us tube type guys are getting up there in age.
Any of us could be here today, and just gone tomorrow. :dontknow:
I'm thinking that most of the amps I'm making will easily outlive me now.
Since I'm not a great musician, I consider these as sort of my musical legacy.
I'm hoping that 50 years from now, some kid will still be rocking out with one of my amps. :icon_biggrin:
-
Well back to the Hot Shot 48. Little progress---got power supply board and main board drilled, chassis drilled for standoffs and a test mounting to see how it fits and looks. Next installing turrets. Not much but something!!! Looks pretty rough don't it! :dontknow: Platefire
-
Got s question? Please look at attached PDF and see view of main board with components.The bias voltage circuit output goes under board to the 220K bias resistors. It crosses path with the under board B+ to PI. I usually try to avoid these kind of intersections but in this case seems unavoidable. Is my concern unwarranted or is there a way to route around I haven't seen? Platefire
-
No problem with those wires crossing. But your bias diode is backwards on the layout.
-
OK, thanks sluckey! I want worry about that anymore and thanks for pointing out the wrong direction
On bias diode. Dummyload produced the original, so I'll just mark it on my hard copy. Platefire
-
I never revised my Schematic when I decided to change plan from tube rectifiers to diode. Attached is the update. If you see any problems, please let me know! Platefire
-
What voltage are you seeking for your B+?
It looks like you will be around +600V with what you have there. :dontknow:
-
Plates drawing shows the B+ as choke loaded as opposed to cap loaded, B+dcv will be lower.
-
You have a PI wiring error. Make the changes on the attached pic.
Your B+ will be fine.
-
> Your B+ will be fine.
With 2.5 Henry, looks like anything under 120mA (cold bias, but also start-up, also stand-by) it will be rising toward 550V, thus threatening to electrolytic caps.
Hammond used a bottled rectifier (slow start), no standby, and also drew a lot of Field Coil current all the time, so they could be sure it stayed near the 0.9* choke-input range instead of the 1.4* peak-catching range.
Many Hammonds also used 600V oil caps just to be sure of no blow-up when tubes and speakers were yanked. If those oil caps are lost (or never fitted), then I'd be thinking 2*350V caps stacked.
-
With 2.5 Henry, looks like anything under 120mA (cold bias, but also start-up, also stand-by) it will be rising toward 550V, thus threatening to electrolytic caps.
Had not considered that. The PR-40 uses PM speakers so there is no constant current drain on the power supply.
Why did you decide to abandon the dual 5U4s? I think I'd put them back.
-
> the 0.9* choke-input range instead of the 1.4* peak-catching range.
I did notice the 1st E-cap was after the choke, instead of before as seems more common.
These type of design issues often escape my repair tech only trained eyes. So I'm learning.
Thank you PRR! :icon_biggrin:
After thinking about it a little, am right to conclude that in this configuration the choke limits the voltage to .9*
because it is resonating with the large amount of AC ripple still contained in the just rectified DCV?
Is this also used as a common technique to drop some voltage without creating a bunch of heat? :dontknow:
-
The reason I abandoned the 5U4's is Dummyload tested the same circuit I am building with the the Hammond PR-40 power supply with SSR. He said the voltage spiked up to 540 for a few seconds and then went down. Read reply #118 on page 3. I have 600V filter caps I am installing. I don't have to have the standby switch but I'm a church player and have to get up and down to play for different parts of the service. When you do that, it's nice to have instant sound and instant mute. Platefire
Thanks sluckey for catching that wiring mistake on PI, revised sch is attached.
-
After thinking about it a little, am right to conclude that in this configuration the choke limits the voltage to .9*
because it is resonating with the large amount of AC ripple still contained in the just rectified DCV?
Is this also used as a common technique to drop some voltage without creating a bunch of heat?
Time to learn how to use the search feature here. :l2:
You will find the info on other threads here, no need for a rehash.
-
:grin:
-
So trying the glean something out of all the discussion, PRR I think? is saying if I use a standby switch I need a pre-standby cap arrangement like a twin with the two 100/350 caps/220K resistors? Would this help with what I'm trying to do? I think I may have room to add it if need be. Platefire
-
PRR I think? is saying if I use a standby switch I need a pre-standby cap arrangement like a twin with the two 100/350 caps/220K resistors?
No, he's not saying that at all. His concern was for the voltage rating of the caps in your schematic as drawn. He did not know you were using 600V caps.
You cannot put any caps before the choke. The choke must remain the first thing your rectifier sees. If you put a cap before the choke, you no longer have a choke input filter. You will have a more common cap input filter and the unloaded B+ with that PT will soar to 440 x 1.414 = 622v! :huh:
-
OK, you got me a little cornfused(not hard to do) because I was using as a reference the attached twin sch that does have caps prior to the choke---or were you just referring to my specific situation in this case with the Hammond Choke. Platefire
-
We covered all this back in December. Go back and read it again. That Fender PT only puts out 340VAC. Your PR-40 PT puts out 440VAC.
BTW, you should at least reconsider your rectifier choice. You have a unique opportunity to build one of the original "Dual Rectifier" amps. How cool is that?
-
I may would have gone with the 5U4 rectifiers if you had got to me earlier but at this point it would require too much back tracking---so I'll go with the SS. Platefire
-
Please have a look at this. I'm soldering connections on my board and got to looking at this bias circuit double checking things. Something don't look quiet right where the board drawing shows connection to bias pot term 1 & 2 as compared to what I have got on the schematic.
It seems to be a conflict the way the bias voltage is going through the bias pot prior to going to the 220K bias resistors on the schematic and then on the board drawing the bias pot is hooked up in conjunction to the 220K resistors?? It appears to me on the schematic, the bias pot has the jumper from term 3 to 2 instead of 1 to 2 as indicated on the board drawing.
I know the bias diode on the board drawing is pointing the wrong way, so I have reversed that!
Also on the 33K resistor I am assuming since it is not on the board would be just connected to
the bias pot term 3 to ground.
I'm a little confused on this, please help. Sch and board drawing is attached. Thanks, Platefire
-
Schematic is wrong. Is this better?
-
That is Better! Thanks for clearing that up for me sluckey :icon_biggrin: I did revise the schematic to reflect the change and also I rearranged the jumper on the bias pot so the connection would be to terminals 1 & 2 from the two 220K bias resistors intersection as to agree with Dummyloads board note. Revised Sch is attached. Platefire
-
Getting close to where I can start wiring it up. Sowing up little small details like grounding points/lugs first. Platefire
-
Fixing to get back on this, so I'm bumping it up to make it easier to find. Platefire
-
Starting to wire things in. It's been a very busy summer that seems to be still going on.
So I just been hitting a lick here, a lick there as I can work it in. With 12 grandchildren, there
Is something always going on :dontknow:
-
With 12 grandchildren, there Is something always going on :dontknow:
Time to start them younguns to work on building Grampa his amps. :laugh:
-
:icon_biggrin: I could have some choice words regarding that, but I'll just keep my mouth shut :lipsrsealed:
-
To me or do you mean family? Sorry if I said something wrong Plate, I meant no disrespect to you or your family.
-
Oh No, didn't take it that way. What I was thinking was, it would be more work to get my grandchildren to work than do it myself. There I said it. Don't get me started---the whole discipline thing has turned on it head since I was a kid but that's another subject for another thread. Platefire
-
Oh No, didn't take it that way.
Good, just wanted to make sure. :wink:
Don't get me started---the whole discipline thing has turned on it head since I was a kid but that's another subject for another thread.
:laugh: Yes it has and yes it is a whole another thread.
-
I'm not that easy offended Willabe, you'll haft to try harder :l2:
I'm getting the old spare parts clone pretty much wired up. I try to wire up as much as possible
before I strap the transformers on then the chassis gets really hard to move around, those transformers are big bruisers.
Taken off on a little fall tour with my wife to celebrate our 50th anniversary. Going to head up to Branson, Mo. Then drop by Salem Ark. on the way back where my Grandparents on my mothers side lived. I had some great times there as a youngster. So the Hot Shot 48 completion will be delayed yet again. Of course there will most likely be tweaking after that(initial fire up) and then a wood head cab to house it in. Platefire
-
I'm sure I just read a reply this week stating you had completed this amp and had been playing it a while. Am I mistaken? If not, what happened? As much time as the forum has invested in this we need to see some pics and even hear some of that good gospel rock 'n blues.
-
I'm with you sluckey ??
-
I messed up, I was talking about the Snake Head Pro Reverb and accidentally posted it on this thread. When I realized it, I removed it and re-posted on the right one. Just let me have my senior moment guys! :think1:
-
I had to ask because I thought I was having one of those moments too! If you read my posts you'll see I've had more than one recently. :laugh:
-
I have a PR-40 Power supply .... well it will be here in a couple days. Went looking for something to build with it. This thread is very interesting , being just a novice I've been lurking here.
-
Well I finally got back on this thing today and installed the PT. After I got it installed, I decided I would run a voltage test to see if the voltages are good. So all I got hooked up is the power transformer wired up to the power switch, Fuse, pilot light, power supply diodes and the bias circuit---as shown in the attached pictures. The voltages readings are recorded on the Power supply drawing(sch below) drawn by Dummyload. My readings are contrasted with Dummyload's earlier readings on his PR-40 PS with larger text, highlighted and in parentheses. Please disregard the choke and filter caps, they were not connected on my amp yet--- Only the filter caps in the bias supply. Please check me out and see if everything looks OK. My DCV output from PS diodes is considerable higher but mine is unloaded and his might be loaded? Platefire
BTW-Frankenxtien----I should have this completed in a few days and will be posting the first test. Stay tuned! Planing on completing it over the holidays.
-
That's fine if you don't intend to use the 4Ω tap.
My heart is beating faster with the excitement! Hurry up Plate! :icon_biggrin:
-
Yeah Thanks, I deleted my question because I looked on my schematic and it shows two jacks, 8 Ohm and 4 Ohm sharing the common black with a switch 4 Ohm to ground when un-plugged on the 4 Ohm tap. I think I'll go ahead and do it that way since I've got it drawn that way. That would make the NFB hookup a little more normal:>)
Yeah I installed the Choke and OT tonight and doing miscellaneous wiring/soldering. My goal is to have it running before Christmas. Sooner the better. Platefire
-
with a switch 4 Ohm to ground when un-plugged on the 4 Ohm tap
Don't connect anything to the switch lug on that 4Ω jack (J3). That will mess things up when you want to use the 8Ω jack.
EDIT... Oh, and your presence pot should be 22K, not 5K.
-
sluckey, you must be having a senior moment----the 2204 and 1987 model Marshalls both have 5K Presence pots. Even the original Bassman that they were modded from has a 5 K Presence??!! Platefire
-
There are more than one 1987 and 2204 amps, JMP series and JCM-800 series. Your presence circuit matches the JMP 2204, but not the others, nor does it match the 5F6A Bassman circuit. Sorry for my confusion.
-
Thanks for the nice schematic comparison! What would make the 22K the one? Was it determined on later model's that 22K worked better or what? Platefire
-
> What would make the 22K the one?
The pot is across a 5K fix resistor. The pot has to go much-more than 5K to be "no effect". 22K is not really "much more". However the pot also has to go much-less than 5K to give "big effect". A 50K pot gets too twitchy in the range zero to 5K. 22K is a practical compromise.
This is not essential. The form with a 5K pot works fine, but the Presence never really goes away.
-
Thanks for the explanation PRR. I really have a hard time really detecting the effect of a presence control---in other words, not very dynamic a change. Best I can tell the amp seems a hair brighter with more presence. I usually just set it half way and leave it at that. Maybe someone could tell me what to look for or I should expect for with that control---but to me it don't seem to have much of a effect.
On another subject---NFB---My speakers all have 8 Ohm loads, so I will be using that tap for a single speaker jack. To my understanding I need to use the 4 Ohm tap with the NFB. I really don't want to install a separate 4 Ohm jack because I'll never use it-----soooo how about I run the OT 4 Ohm tap up on the board and solder it to the NFB resistor turret??? I would like that better than installing a 4 Ohm jack just to run NFB to---Huh? Platefire
BTW- I cut and pasted this information on the Presence control of Marshall Plexi History:
Earlier Marshall amps had a 5k Presence Pot with no Presence Resistor in parallel. The Presence Pot was changed to 22k and a parallel 4.7k Presence Resistor was added to eliminate pot scratchiness due to DC voltage across the pot. In the new circuit (shown above) the Presence Cap blocks DC and keeps it off the pot. The 4.7k Presence Resistor also backs up the Presence Pot in that if the pot fails the amp will continue to function. In the old circuit if the pot fails the amplifier will completely cease to function.
-
On another subject---NFB---My speakers all have 8 Ohm loads, so I will be using that tap for a single speaker jack. To my understanding I need to use the 4 Ohm tap with the NFB. I really don't want to install a separate 4 Ohm jack because I'll never use it-----soooo how about I run the OT 4 Ohm tap up on the board and solder it to the NFB resistor turret??? I would like that better than installing a 4 Ohm jack just to run NFB to---Huh? Platefire
You just asked this very same question 2 days ago. I answered then you deleted the question.
Now who's having a senior moment. :laugh:
-
Well this is not actually a senior moment, even though they are plentiful these days. It's more a case
of probably unfounded "Taboo" perceived amp practices. I did size up the situation of installing the second 4 Ohm jack, but I didn't like it because it would put the jack right above the PI tube socket---"whoa Taboo". So the perceived Taboo is--- I've never put a speaker jack right over a pre-tube in that close proximity before--so the reason of my hesitation! See picture. Platefire
-
Don't think of the PI tube as a preamp tube. The PI is actually part of the power amp. If you look at the schematic you'll see that the NFB wire from the OT secondary actually connects to the PI tube thru a couple resistors. My point, it's perfectly fine to put that other speaker jack near the PI tube. I would.
IMO having a 4Ω jack and an 8Ω jack available is desirable. Just don't use the switch lugs on either jack as mentioned earlier.
-
OK, Thanks! I'll put her in there. Platefire
BTW-I needed some knobs and heater wire for this amp, so I went ahead and ordered a 25KL from Doug
for the Presence pot. I suppose a silly 3K won't train-wreck the operation:>)
-
I thought I would post the schematic of Doug's 50 Watt Plexi with Hot Switch which is what my design is based on. The fact that I am using a Power Transformer and Choke out of a Hammond PR-40 Organ Tone Cabinet puts a little bid different twist on the power supply. DummyLoad helped much with the original design including the drawings/schematics/Test on his PR-40 power supply to provide help/design of the power supply. DummyLoad is no longer hanging around here so I would like to say a big old Thanks! and hope he's doing well. If you run though all the post, many have contributed along the way--thanks! Sluckey has also helped me much along the way and still is, I appreciate that much. I am getting close to the end and expecting good results---but there will always be some corrective tweaks! So for anyone following this project I think it's important to see Doug's schematic compared to mine. So Doug's schematic is first and then mine. Platefire
-
Question? Getting ready to wire up V2 Socket. Regarding V1a I have a plate resistor on my schematic of 330K. Researching this I find the model 2204 schematic has the 330K and the model 1987 has a 100K plate resistor. Also Doug's 50 watt Plexi with hot switch that my design is based on has a 100K in V2a.
So I'm inclined to think it should be a 100K in that position but my question is---why did they use the 330K on the 2204 to 74VDC---more distortion? Would kind of like to understand it before I install. Platefire
BTW-If you would like to view a 1987 and 2204 schematic, they are attached--
-
> why did they use the 330K
An obvious answer is: less heater-cathode stress.
As there is another stage of gain before the power bottles, this is still not the primary distortion point.
I doubt it is a huge difference, but you could compromise on 180K.
-
Thanks PRR, I went ahead and dropped a 100K in there to be consistent with Doug's. It can always be changed latter if it needs to be. There usually always is some tweaking on a new amp anyway. Platefire
BTW-----All done except heater wiring
-
Fired up the Hot Shot 48 first time Wednesday about 1:00 PM. Tried it on a light bulb limiter first without tubes, then with tubes and everything seemed good so went ahead with full fledged voltage. Everything seemed to be working well. Clean channel without hot switch worked well and even sounded kind of fendery to me. The hot switch was some fine sounding distortion. Very thick, rich and very Marshally sounding I would say. The amp seem just a little noisy with hum to me especially when the hot switch kicked in.
I did a complete voltage check and adjusted bias. The power tubes were a new matched set of EH EL34's. Not very well matched IMHO at 8mA apart. At 385V plate voltage I set to balance between the two at 35.3 mA/43.1 mA
Before I had a chance to test is very much, I had a major accident. I was re-checking the plate voltage on V5 EL34 and my MM probe slipped touched the socket heater terminal at the same time and flashed brightly:>/----then no more sound. The PT was still working but no sound. All of a sudden checking voltage there was a 624VDC coming off choke. I figured I had taken out the choke or the OT or both.
I was so disgusted, I just put everything up kind of sick at heart. So I pouted the rest of the day in disbelief that I had done such a stupid thing---so close then blew it.
Well today Thursday I finally recouped myself well enough to check it out. Still building up to 624VDC after the choke but nothing on the EL34 Plates. After messing around with it for a while trying to figure out what was going on, I finally put a jumper cable over the first 5Watt 100 Ohm resistor---Bingo---the amp came back to life--plate voltage on EL34's normal. So instead of taking a major item out is was just the first power resister after choke. All the voltage from the power supply was accumulating on the first filter cap and was stopped on that open resistor. What a relief--happy again!
Attached is the schematic with all the voltages readings and all look good to me with the exception of V2b at 197V and the D rail shows 274V. With no resistor between that, should be 274V? I'll check that out further plus the hum issue when I get my resistor in, none that value in stock.
Looking forward to getting a new power resistor in to play around with it some more. Just thankful that a resistor is all that got damaged in the accident. Platefire
-
V2b at 197V and the D rail shows 274V. With no resistor between that, should be 274V?
Correct. You should recheck that. Maybe just an operator error.
I would completely remove R32 and C16A.
-
Apparently you think R32 and C16a is overkill? Not sure why Dummyload designed it that way. I know
on the PR-40 power supply he tested with diodes I recall him saying the voltage spiked up real high for a few seconds before coming down to working voltage---may not be the reason at all? For sure that's why he recommended the 600V caps.
So do you think those two components could be having a negative effect on the amp? Thanks, Platefire
-
Not a negative effect. Just not necessary. DL was thinking you may need to drop the B+ a bit but that's not the case. Those EL34s will be happy with 400v or even higher. The 100Ω will cause the B+ to sag depending on load. That may or may not be desirable.
You've seen how high that B+ will go when that resistor burned open. No current flow (load) causes the swinging choke to not do it's thing and the B+ will rise to it's maximum amount.
-
Thanks, sluckey. I'm going to leave it as is for now. If it gets to loose and flabby, I'll remove it latter to try to tighten it up.
i got a 5 watt 15 Ohm from a amp tech friend in the next town and put that in there today. I think is sounds better than my Dukane Bassman. It's just seems to have more depth or thickness. The wife and I ran through some of our JamMan songs using my Hwy 1 Tele and it made the tele sound big. Takes pedals well. My experience has been very good so far. It was operating very quiet at the volume I was running it tonight.
I did double check that V2b plate voltage and it was same as the D rail as it should be. The voltages all picked up a volt or two with the lesser Ohm power rail resistor. . Platefire
-
You did a good job with that. I bet it becomes one of your most favorite amps. The transformers look like little soldiers standing at attention, just waiting to follow you anywhere.
-
Those are some big soldiers! :laugh:
-
Forward March! Hulp two three four>>>>>>>>Charge---->------>
As I recall those solders are standing up erect and at attention because sluckey told me about "L" brackets I could get to mount them this way. Up to that point I was scratching my head how to mount in a used chassis already full of holes. Think I'll name that PT "Mad Dog" after the new appointed General%>/
Something I played with this morning---being the type player who likes the old bluesman's approach to using my guitar volume to nudge cranked tube amps to go from clean to dirt, with the hot switch engaged and the pre and master vol's at low settings, you can go between clean to scream pretty successfully with a little practice managing it. Makes me kind of interested in hearing how Doug came up with that design. Platefire
-
It's very nice , the cap$ , OT , tubes , I'll say there is a power supply available here in Memphis until I get enough nerve$ to build with it. :icon_biggrin:
Very nice , thank you for sharing your design.
-
Your Welcome. All I can say is these folks at this forum has been helping me through builds for 15 years and they are the most friendly and helpful folks on the planet.
I bought a piece of wood today at LOWES and going to start on a head cab for it. Right now the bottom of the chassis had no cover plate and it's just open. So I need to do something about that. Platefire
-
Right now the bottom of the chassis had no cover plate and it's just open. So I need to do something about that. Platefire
Put the bottom shield in the cab. Just glue/staple some heavy duty aluminum foil to the bottom of the head cab. Or use some metallic screen wire. Or my favorite, 3"wide aluminum duct tape.
-
That had crossed my mind, if I needed to do that? It is on every commercial amp I'm sure for good reason. Thanks, I'll just have to decide what I will use. I kind of like the idea of the duct tape but just wonder with it sitting under the chassis, can't help but wonder if the tape would tend to pull up with weight of the chassis sliding across it when taking the chassis in and out. I might need to find something tougher because the chassis is really heavy with those big transformers. Platefire
-
> if I needed to do that?
You don't need it until the day you NEED it. Working a club or garage with ugly electricity. Working too close to a broadcast transmitter, or the CB and Police radios at the truckstop tavern.
I've been embarrassed often enough (polka-hour radio in the harpsichord recording) to want to do all the "easy" things before Murphy can find my build.
-
Hay PRR, definitely don't want no Polka creeping it there :help: or 10-4 good buddy!
-
Worked on this amp several hours today. First it was the noise problem then second was the unbalanced power tubes about 7 to 8 mA differance.
I spent a lot of time checking lead dress, grounds and looking for some kind of short but never ground nothing and the noise didn't change. Even put the bottom board of my head cab over the bottom opening side of the chassis with a piece of tin foil but still no change. I finally gave up on the noise issue and moved to the biasing.
I had recently bought an extra new single EH EL34 to hope I could somehow match it with one of the existing so called matched set to hopefully get a better match. So I checked the existing tubes first at 385 VDC/38.3 mA abd 385 VDC/46 mA.
So I pulled the one running 38.3 and put the new tube in that slot at 45.2 mA/49.3 mA---that's a little closer but a little too hot.
Checked the voltage and both plate voltages had gone up to 390/390. So I reset the bias 40.7/39.6---not hot but not cold either and very well balanced.
Ok so I'm done, sitting my amp back on my speaker and it hit me, try a different preamp in V1, 'V2 and V3 that seemed to be kind of useless because they are all suppose to be new. Well I started with a known good replacement with V1----Wow somethings different, all of a sudden I begin to realize most of my noise is gone>>>>I just would of never suspected that. So I had all new EH tubes in it but now one used Groove Tube in V1 that sounds real good. Still a little noise but not nothing as much as before. So I'm very thankful for a little success balanced power tubes and and a quieter amp :happy1: Ye haw! Platefire
-
8mA unbalance is totally fine for EL34, which will typically perk-up to 250mA when actually playing big.
You do not want either tube over-heating, or sitting dead. But a 50:30mA unbalance may have almost no effect on "sound".
> they are all suppose to be new.
I pulled a new holiday-light string out of the box. 1/4 of the run was dark. Tubes are not made a whole lot better than holiday lights. New does not prove good.
-
Yeah I know that close of a match is overkill but it's a nice Christmas present to have my new amp finally whole and healthy. Thank you Lord! Platefire
-
Got an issue with this one I've been noticing lately. A frying noise that I assumed was pre tube messing up. I subbed V1, 2 and 3 with a known good tube with no change. I got to playing around with the controls and it seems no other control effects the volume of the frying like the treble control.
Turn it down and almost non existent and turn it up and it gets louder.
So the first thought that came to mind was the 500p Silver Mica Treble cap but I don't ever recall one behaving like that.
I haven't tore it down yet to check anything internal. Anyone got any ideas on this? Platefire
-
I assume turning the master to zero kills the frying noise? If you turn off the hotswitch does the frying go away? Change the three 100K plate resistors in the preamp. Also change the 100K cathode resistor.
-
Thanks Sluckey. The master kills it. The hot switch is noisy with white noise but no frying. Only frying with the hot switch off. Platefire
-
Is the SM cap good 500V rated?
Used to be they all were. In recent years you can buy 50V rated. With the variations of natural Mica, this might stand 250V for a while then start to break-down.
I think for the bench-cost of 500p, replacement beats thinking.
Or just remove it for a moment. Sound will be dull, but if the frying stops that's some confirmation the cap is sick.
-
I did a little more testing. Put it on standby(SB), pulled V1, turned the SB off was still frying. Put it on standby again and pulled V2 and turned SB off----no more frying. So what does that prove?? nothing related to V1? Not power tubes with MV down no fry. So that puts it at V2 or V3 and since the treble control severely effects it, that would put it down to V2 and tone stack at most likely culprits.
Am I thinking right? So the V2a 100k Plate R mounted on V2 socket, the V2b 100K cathode R and the 470p treble cap would be the most suspect in that area? Platefire
BTW--on the SM, I really don't know for sure if it's rated a 500V---it should be! but I couldn't say for sure until I take the bottom plate off and have a look.
-
Could this be oscillations?
silverfox.
-
It don't act or sound like oscillations. It's just a low level static, mild popping, not loud at all but just enough for me to know it shouldn't be there and bug me. Turn the treble to 9:00 UN-audible, 12:00 barely audible, at 3:00 audible. I just got through playing about an hour on it and it sounds and operates great, just need to stifle that little gremlin. PLatefire
-
I think you want to pull the cover and replace that treble cap.
For motivation: if that cap goes from leaky to dead short, it wants to put big DC on the next grid, which is not a good thing.
-
Yes, Thanks! I really shouldn't run it anymore with this possibility looming.
I checked my inventory and couldn't find one of the brown SM caps like Doug sells, but found
A black one I think is NOS. This is 500p isn't it? Pretty sure it is, please verify.
Platefire
-
This is 500p isn't it
Yup, believe also Doug sells those, or did
-
The SM 500p was the culprit. It was rated at 500v too. Thanks so much for conferring with me to find it. It's quite as a church mouse now and I'm a happy camper now. Let the Jamming continue.
:m8 Platefire
-
SM 500p was the culprit
FWIW
That 500 in your pic, I've had a very high fail rate, like 1 in 3. bought over time.
-
Are you referring to the black SM or just SM in general. I've always had the brown SM and this is the first one I had failed in 15 years. I think I got the black one here in some NOS caps I bought about 10 years ago at a thrift shop. Platefire
-
The black one's, I've got them isolated so I don't grab by mistake :laugh:
-
OK, Thanks for the warning. Next time I order from Doug I'll get several brown SM 500p's, seems like they are always in demand. Platefire
-
Platefire,
Great job on the amp! And THANK you for sharing the schematic with voltages! I put your SCH schematic in the SCH Library of schematics. IF you have a layout to share that goes with the schematic, can you please add it also.
The link to your schematic is here: http://el34world.com/Forum/index.php?topic=21357.0 (http://el34world.com/Forum/index.php?topic=21357.0)
With respect, Tubenit
-
Thanks tubenit
I don't really have a layout for the whole amp. I started one using ExpressPCB as a format but there was so many amendments to the plan along the way I never brought that layout up to current. It's a real headache using that program for a layout IMHO. I might try to resurrect that old layout and see what I can do with it.
I do have a layout for the board layout that Dummyload created for me but it has a few mistakes on it that I can't correct because I don't have the drawing program he has. Here is the last version he provided. Platefire
-
If anyone is interested, I had another post regarding my find at GoodWill warehouse sales. A PR-40 cabinet. I've got one of those power supplies sitting here and don't expect I'll ever use it. Let me know if there is any interest.
silverfox.
-
Yes, it seems kind of appealing but the shipping would be major
On that heavy buddy! Talking about a boat anchor :laugh:
-
Making progress on the head cab. A few pics! Front and rear panels coming.
Thinking of finishing it with black tolex. Platefire
-
Turn the page! Cut out new front panel for this amp yesterday. Gosh, ain't that Jesus reaching out to the Whole World? :icon_biggrin:
-
Hello Yall!
I've been playing the Hot Shot 48 at my regular gig at Church last 3 weeks. I finally finished tolexing the cab but Haven't taken detailed pictures yet. I've been playing it with the hot switch off in clean mode. The amp is very quiet regarding operating noise in clean mode. I don't detect any noise at all unless I just listen for it. That's great because I like a quiet amp.
The most distinguishing thing I can tell about it is not as bright as my 5F6A build(Dukane). Seems I'm fighting over brightness on that build but on this one, not so. I've been playing a 69 tele through it lately and have no problem dialing in enough bottom to mellow that bright ax out. I modernized the presence control at I think sluckey's recommendation and it's one of the most responsive ones I've had where I can hear the difference in settings. Real happy with the tone stack operations and MV isn't bad either.
I want to get around to playing with hot switch settings but for my break in period hanging with clean with MV set to present a little hair at top guitar volume, clean when turned down.
Here is a picture of the Pastors Grandson came up after church and took his picture with me. He's a guitar nut already:>) You can see the Hot Shot 48 in the background sitting on a Mesa Boogie 4-10 cab. Platefire
-
That is a nice amp you've built there. Slowly but surely moving closer to a build with my PT (same PR40) There's a Thordarson PT that pushed it back a bit in the lineup but both are waiting on the last build , 5e3 Pro Amp (wire dressing) I had to build a few boxes out in the backyard with the nice weather so now that's done.
I don't play out much anymore and the need for another amp is ... well .... need someone else to build it for :wink: With six amps ready to use , I'm beginning to feel like a hoarder. Time to clean the studio up and have a few pickers over to test some earplugs.
Being a humbucker user pretty much exclusively , has me wanting that bright sound. Thank you for sharing your experiences .... Great picture :wink:
-
Thanks Frank
This makes 15 amps I now have. Think this might be my last build. Just maintenance or tweaks on what I already got from now on. It took almost two years to complete this one. I've been practicing with two amps together lately, not stereo but a mighty full wide sound.
I did some builds for other people but if I charged for the labor and cost I really had in them I would have had to charge them a small fortune, so you end up eating research time and other time to make it happen. This is good fun if you like building for the sake of building but if it's not profitable, not much incentive to continue when there are more important things of life you could be spending your time on that really need attention. On the other side of the coin, it's nice to spend time doing something you really enjoy too. So I look at it as a fun hobby with great tonal benefits!
Would like to see what you make out of your PR40 transformers. Rattle my cage when you get going on it. This is a very long thread and I think definitely just about every aspect of the build is well covered. Casey4s the one who talked me in to building my first Champ in 2000 and then provided a hand made kit to accomplish it, taught me to document everything very well, and I guess that is etched in my brain. Platefire
BTW-I will post some detailed pictures of the amp in the not to distant future, if the Lords willing and the creeks don't rise :icon_biggrin:
-
You really touched on quite a bit , that rings true for me.
Trying to be practical/thrifty has me thinking of building something along the lines of what it was powering.
Not doing what everyone else does , probably drives anyone who builds amps to start with. It's strictly fun for me ... TriFi something to use with my electric piano/midi. Maybe something to double as a small PA for here at home. It's a tiny house so we don't need too much.
Not like we don't have large speakers hanging from the ceiling in what was the living room. My son and I have played together for years. The dinning room table was replaced long ago with a Drumkit. I'll let you know when I start in on it :wink:
-
if the Lords willing and the creeks don't rise :icon_biggrin:
don't move, they're rising FAST in MI!
-
Yeah, I'm waiting for it to dry out enough so I can mow
My yard, before it gets too high!
-
I normally put finish pictures up when I finish a project but when I finished this one, I took it to our Church where I play with the Praise Band and its been there ever since. That was March 17. Some of the tolex that wasn't glued well enough has come loose along the edges, so I brought it home to re-glue those ends.
So for all of you that have been sitting on the edge of your seat, chomping at the bits, pacing the floor and biting your fingernails in anticipation---the pixs are here!!! :happy1:
Yeah Right! :rolleyes: Anyway it's something I must do, so lets get it over with. Platefire
-
Oh Yeah, there is even more!
-
Not a whole lot of beauty here, just neat, efficient and BTW---it sounds great and quiet as a mouse!
-
Sweet build, Plate!!!
-
Thanks! I'm kinda fond of it. Platefire
-
Love it. really good job of making use of an old tone cabinet. I love to get those things and what is cool is I usually get them for just hauling them off.
I am really impressed you are able to use this to play at church. Must get a good tone early, which is rare for a Marshall Topology.
-
Thanks Ed! If you look at the pictures of the pre-vol and master vol
That's what I'm running my strats and teles on. Pre is less than 12:00 o'clock
and master below 9:00. With my humbucker guitars the pre vol right above 9:00.
So IMHO I'm getting good response and tone. What I like is I don't have to
Fight ice pick highs like on some of my other amps. The good thick tone is
There still with good cut through highs. Better than my Bassman builds but
In actuality, it is a modified Bassman build. The Presence control provides a
more detectable tone change in adjustment than any one I've had before.
There is a good reason it's been at the Church the last six months, it's really
Working good! Platefire
BTW---Have to give credit where credit is due. DummyLoad was there step by step,
Blow by blow in working with his own PR40 power supply in determining what
Would work best plus he actually did the drawings on the board. So even though
Others provided helpful hand that I very much appreciate, DL went to a lot of extra
effort beyond the call of duty, so SALUTE to you Dummyload!!!!!
-
thanks plate and you're welcome!! happy to chip in.
--pete