Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sluckey on July 13, 2017, 12:29:31 pm
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I've finally started this project. All parts have been received and the build is under way. I'll eventually make a web page for this amp, but I have a lot of other stuff going on right now too. Meanwhile, here are a couple pics of completed chassis work to give you an idea what it's gonna look like...
EDIT... here's the layout document... http://sluckeyamps.com/supro/supro.pdf (http://sluckeyamps.com/supro/supro.pdf)
(http://sluckeyamps.com/supro/s-01.jpg)
(http://sluckeyamps.com/supro/s-02.jpg)
(http://sluckeyamps.com/supro/s-03.jpg)
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Nice as always! I'm looking forward to getting your take on the 1 knob tone n if you tweak it. I need to get my project from a 2 knob to a 1 knober, so please don't patent it yet :laugh:
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The 6424 has two tone knobs so I won't be tweaking for one knob. Look at the 1624 schematic if you want to see the one knobber version of this amp.
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6424 has two tone knobs
the schematic you posted on another thread shows 1 knob for each side of V1, so ya 2 total, same as I'm thinking of doing, currently I have 2 per side.
If I looked at it correctly they are the same 500pf, .0033uF, 500k.
I'll steal that as a starting point.
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Subscribed.
Hi Steve - what VA rating is that variac on your bench BTW? (if you don't mind me asking - only it looks like of compact/smallish - like 500VA or something. I was wondering about picking one up for myself, but didn't think that 500VA would be big enough. If it is 500VA, how do you find it for your stuff?)
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Excellent!
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Hi Steve - what VA rating is that variac on your bench BTW?
It's rated for 0-140V and 10 amps. I sold a 5 amp Staco earlier this year. 5 amps is big enough for everything I've messed with. 10 amps is what I've seen mostly in the old repair shops. If I had to buy one I'd shop for a 10 amp model. A built in volt meter is very handy too.
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And, if you would like a variac that does not hum and vibrate, then get one rated for 240V and run it on 120V. Unfortunately, the current rated does not double, it stays the same.
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Steve,
Great looking project looking forward to this. I had a custom 1-15 cabinet built and will be tackling a Supro T-bolt one of these days.
Mark
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Thanks Mark. I've been following your project over on TAG with interest. Looks good too.
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> 10 amps is what I've seen mostly in the old repair shops.
The original GR Variac was rated 10A. Many clones were also. In days of 15A circuits, a 10A would handle nearly any load. The "10A" is conservative and you can beat it considerable for occasional use/abuse.
Smaller ones don't want to cost a lot less-- wire core and labor don't scale-down real favorably. Of course smaller/larger ones did appear, under 2A to over 30A. I just got a 5A which I plan to use on a 3.6A furnace blower where it may be loaded 23 hours a day. (I ended up with the small fan on the extra-small burner and it blows a lot of hardly-hot air; I can reduce the blow for the same heat in warmed air and less draft.)
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Got the board built today. Too hot to do any more...
(http://sluckeyamps.com/supro/s-04.jpg)
(http://sluckeyamps.com/supro/s-05.jpg)
(http://sluckeyamps.com/supro/s-06.jpg)
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Real nice looking so far! You always make nice neat looking amps!
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I got the board laced and loaded today...
(http://sluckeyamps.com/supro/s-07.jpg)
(http://sluckeyamps.com/supro/s-08.jpg)
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Man you just throwing all the mojo out. MF Resistors, Illinois caps, and Chicklets? Have you gone mad sir? You know it will now sound like a modern Mesa Boogie, is this really what you want being an old surf junkie?
How hot is it? Why didn't you air condition your workshop? You've got enough money to air condition a cotton field there in LA.
Is this where you play guitar too?
:laugh:
Looks great and really a fun amp. The tremolo is outstanding. Is that Black Fiberglass Board? It looks like it has graphite on it.
The lone turret under the pot on the front of the chassis, did you not drill through? Use a bottoming tap. This support for your preamp ground bus?
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Man you just throwing all the mojo out. MF Resistors, Illinois caps, and Chicklets? Have you gone mad sir? You know it will now sound like a modern Mesa Boogie, is this really what you want being an old surf junkie?
I've set my sights pretty high on this one. I'm gonna be able to play the opening to "Whole Lotta Love"! :wink:
How hot is it? Why didn't you air condition your workshop? You've got enough money to air condition a cotton field there in LA. Is this where you play guitar too?
Low 90s with matching humidity. I'm still trying to raise money for an AC unit. Not to worry though. The pool is only 20 steps away. And I have a refrigerator in the shop. I prefer to do amps during the winter.
Is that Black Fiberglass Board? It looks like it has graphite on it.
Yes. Got it from Doug. He calls it FR4/G10. It drills and cuts easier than his green board. The board is jet black but the fluorescent lights put a "washed out" sheen on it. Haven't been able to get a good pic.
The lone turret under the pot on the front of the chassis, did you not drill through? Use a bottoming tap. This support for your preamp ground bus?
The turret is soldered to the back of the pot. It supports the two mixing resistors from the two volume pots. Look at the layout and schematic.
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I'm still trying to raise money for an AC unit.
I got an 8ton unit with a couple issues, but it's free :icon_biggrin:
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I see the Visio work now, you added it.
Your schematic drawing is much easier and logical to read, but it doesn't show a switching pot. It took me a bit to find the shared cathode site you have them reversed. Are you planing a pull pot to slow the tremolo even more or is it simply to stop and start?
I see you have a switching dual input. I do this a lot now myself ever since the AC15. Just a simple thing, but it adds so much to the tonal versatility to an amp. Since the wiggle channel has more gain and headroom, I am surprised you duplicated the tone stack.
I wish I could play :sad2: Even if it were only Whole Lotta Love. Finger doesn't look a lot better yet. 120 grit on a belt sander will remove fingernail and skin quick. I just hope it quits bleeding in a day or 2.
Nice work as always!
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I'm still trying to raise money for an AC unit.
I got an 8ton unit with a couple issues, but it's free :icon_biggrin:
Shooter, he is full of more crap than a Christmas Turkey!
Trying to raise money. Yea, I believe that. No, he is just used to the Mobile area where when it is not hot, you better leave cause a hurricane is on the way. I hear the older you get the more you prefer the heat. I also hear you ears do not quit growing and I already have plenty. :laugh:
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I got an 8ton unit with a couple issues, but it's free :icon_biggrin:
Couple issues??? Are you saying it actually took two lightning strikes? :l2:
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The pot switch simply turns the trem on/off. Just trying to keep it true to the schematic but mostly it's s good way to mount that 2.2M resistor. :icon_biggrin:
I got my index finger jammed between a disc sander and the sanding table on my ShopSmith once. It came out once I had sanded it enough.
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Looks like all I'll get done today is the filament string.
(http://sluckeyamps.com/supro/s-09.jpg)
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It came out once I had sanded it enough.
You folks need to sand like you build amps :laugh:
two lightning strikes?
I wasn't counting, I wasn't seeing very well either! I was upstairs, 30ish ft away when it struck!! The next morning my eyes felt like I had flash burns from welding! It also hit 3 apple trees that had been on the property since late 40's. They have lost most of their bark, most of the upper growth, but still got a bumper crop growing for the resident deer.
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Wow I've missed this much of your build Steve! Good to see another amazing build coming together. But I do see one error. You've got the red and black wires used for heaters when they should be green and white! :P
Look forward to the finished product! My first ever real time sluckey build.
(I missed the first due to being on vacation in Scotland, so I guess that's acceptable :D)
~Phil
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I prefer green/yellow and would really love to have some brown. But I have limited quantities of those colors. Got miles of 20AWG red and black Teflon though! That's the main reason I use it. Plus it makes all the Marshall freaks happy! :l2:
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Got the control panel wired today...
(http://sluckeyamps.com/supro/s-10.jpg)
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Beautiful, inspirational work, as always.. :notworthy:
Love the way you are able to work patiently and just chip away at it. I always get so damn excited I just work and work until my eyes hurt and I need a massage.
I noticed a small discrepancy in your schematic.
The cathode bypass cap on the input triode ("Z" feed from the tremolo) appears to be 35uf/50V on the original, but .0033 on your schematic. I see where you have a 35uf on your layout, so I'm sure it's just a typo.
I found this while comparing values and circuit structure to the 1624T model.
This 6424 and the 1624T are basically identical.
Your documentation is always perfect and I want to keep it that way :icon_biggrin:
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Thanks for catching that. Got it fixed already. As always, if you find any discrepancies or other little turds please let me know.
I'm not really being patient on this project. I would be done by now if I had waited until winter to do it. But I got the hots to do it right now. And that's the problem. It's too damn hot and sticky in my shop to stay on the bench for more than a couple hours! I'm working in a bathing suit so I can jump in the pool with a beer. I usually don't make it back to the shop after that! :icon_biggrin:
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Thanks for catching that. Got it fixed already. As always, if you find any discrepancies or other little turds please let me know.
I'm not really being patient on this project. I would be done by now if I had waited until winter to do it. But I got the hots to do it right now. And that's the problem. It's too damn hot and sticky in my shop to stay on the bench for more than a couple hours! I'm working in a bathing suit so I can jump in the pool with a beer. I usually don't make it back to the shop after that! :icon_biggrin:
Nice project Steve, I've been wanting to build a PP 6973 based amp ever since I "restored" a Gretsch 6161 a few years back. Looks like pretty much the same beast to me. The guy had two of them, one that was completely thrashed (mostly the cabinet and speakers, which looked like they had spent some time underwater) and the other amp was in half decent shape, so he commissioned me to salvage the parts that were in the best shape from either and make them into one functioning amp, and whatever was left was spare parts. So I had never heard played on one of these until I finished the project. Very impressive little amp and very fun to play. I must say, I didn't want to deliver it back to him!
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I must say, I didn't want to deliver it back to him!
That sounds encouraging. Thanks for the info Craig. Thanks for the kind words as well.
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ok, I give, is that standoff soldered?
and
jump in the pool with a beer
doesn't that water down the already thin beer :laugh:
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ok, I give, is that standoff soldered?
Yes. The bottom threaded part is brass. Solders very easy even with my little Weller iron. Just gotta use flux and pre tin the turret and the back of the pot.
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Been following this build with interest. Looks like fun project!
With respect, Tubenit
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Steve,
Regarding my topic of 1624, what power output with your 6424 are you gonna receive?
I think ,I'll follow my build with quartet tube power stage and remain with biasing cathode resistor or resistors.
Regards,
Adam
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I'm expecting about 15 watts.
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Acc.to 6973 data, It should be approx. 17W with 300V at plates.
On schematic we have 350V. So, It might be even more?
Regards,
Adam
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ok, I give, is that standoff soldered?
Yes. The bottom threaded part is brass. Solders very easy even with my little Weller iron. Just gotta use flux and pre tin the turret and the back of the pot.
Haven't seen that before, very neat idea. I use a lot of those turrets and think I'll still just drill a hole and bolt mine on, I'd probably cook the hell out of the pot.
Mark
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Haven't seen that before, very neat idea
agreed, does seem a waste of good threads though :laugh:
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Got the input selector, shielded cables and PT wired this morning. All PT voltages checked out OK. Probably won't get back on this until Monday. Got some dignitaries coming to Mobile this weekend.
(http://sluckeyamps.com/supro/s-11.jpg)
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Got some dignitaries coming to Mobile this weekend.
In Laws? :)
~Phil
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No, they're outlaws! At least one is. :icon_biggrin:
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The best kind bring 'shine.
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Very nice Steve
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I'm building vicariously via this thread. It's looking very nice Steve, and I'm finding nice little touches of yours to steal to include on my build.
Speaking of little touches... On your schematic you've got a 1M input resistor, but the layout has 470K. The original S6424 schematic uses 470K, so I imagine you're also using 470K? I can't tell from the latest pic...
I'm interested in what output transformer you'll use. I'm pretty much restricted to the Hammond line of output transformers unless I want to pay an arm, a leg, and my first born to pay shipping from the States. The Electro-Harmonix 6973EH datasheet gives 17 Watts from 310V plate voltage, 270R Cathode Resistor and 6k load. The closest Hammond Output transformer would be the 1760H, 6600 ohm CT, 20W. Of course, this circuit runs the plates a wee bit hotter...
It's the same story with the power transformer. I'm liking the Hammond 290BEX for this. 315-0-315, 138mA primary. I reckon this'll give me a B+ of around 350 to 370V when using a 5Y3.
I'll need to break out my books and draw some load lines to figure the difference all these little differences will make. 250R, 310V, 6k vs 270R, 370V, 6.6k. Or are all these values close enough for rock n' roll?
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the hammond 1650F 7.6k 25W OT is closer to the original supro part which is 7.5k. :dontknow:
the 290BX will generate about 375V.
--pete
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On your schematic you've got a 1M input resistor
Thanks for finding that error. I've corrected it.
I'm using a PT and OT from a donor Hammond AO-43 amp.
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The best kind bring 'shine.
And they may bring some of that wacky weed too. :laugh:
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On your schematic you've got a 1M input resistor
Thanks for finding that error. I've corrected it.
I'm using a PT and OT from a donor Hammond AO-43 amp.
Do you know the reflected impedance on the Hammond OT? I guessed they were 10K/8ohm, but I have never known for sure.
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Voltage ratio is 1.025:30.6 or 29.85.
Impedance ratio is 29.85 x 29.85 = 891.
So, 8Ω would reflect 8 x 891 = 7128Ω plate to plate. Looks like a good choice for 6973s.
This OT was used with a pair of EL84s in the AO-43 amp and the same OT was used with a pair of 6GW8s in the AO-44 amp. And I used the same OT in my Plexi6V6 and L'il Maggie projects.
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Voltage ratio is 1.025:30.6 or 29.85.
Impedance ratio is 29.85 x 29.85 = 891.
So, 8Ω would reflect 8 x 891 = 7128Ω plate to plate. Looks like a good choice for 6973s.
This OT was used with a pair of EL84s in the AO-43 amp and the same OT was used with a pair of 6GW8s in the AO-44 amp. And I used the same OT in my Plexi6V6 and L'il Maggie projects.
These are perfect for all of those tubes mentioned. I really like them (the Hammond iron). I've also used it for 6BM8s with much success.
Steve, you inspired me to create an amp conversion recently, as many of your amp projects have - and I'd just like give a big thank you for this along with all of the responsive help you provide. :thumbsup:
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I saw your Pathfinder conversion. Looks good. And I love the name. Now you need a "99" to complete the set!
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Got it completed today! The layout works and is very quiet. The amp sounds good and the tremolo is very good. The power tubes were idling at 25 watts with the stock 250Ω cathode resistor. I've replaced that with a 470Ω to cool it off a bit at 17.8 watts. That's about all I expect to change other than tidying up the wiring a bit. Tomorrow I'll update the schematic with my final voltage readings. Stay tuned...
(http://sluckeyamps.com/supro/s-12.jpg)
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other than tidying up the wiring a bit.
Yeah, good Lord it's a real mess.
:icon_biggrin:
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very, very nice! :icon_biggrin:
--pete
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Not sure about the knobs, but I love the rest!
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Gotta raise some money for a full set of knobs. Or steal from another amp! :icon_biggrin:
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You can cut a broomstick for that purpose :icon_biggrin: :icon_biggrin: :icon_biggrin:
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As always very nice realisation Steve :thumbsup:
Franco
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Fantastic job! Well done, Steve.
With respect, Tubenit
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I hope all that summer sweat is worth it to play that mystical Jimmy Page stuff. Nice job, but buy you some chicken head knobs and quit :sad2: about not having money for them. Now you gotta build a Dragon Telecaster.
Nice job!
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Not sure about the knobs
I have the same set! As an abstract artist, messing with ppl's head is fair game :icon_biggrin:
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Not sure about the knobs
I have the same set! As an abstract artist, messing with ppl's head is fair game :icon_biggrin:
Are you sure that is not INSANE artist?
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INSANE artist
some famous human once said, there is a fine line 'tween..............I keep going back n forth seeing which side I like better :icon_biggrin: SSA just sent me my "projections" for retirement, I get more if I stay on the insane side :icon_biggrin:
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We should get together Shooter. I bet we could come up with a full set of knobs between us. If not, surely we could get a very interesting mix! :laugh:
K's broom handle idea seems appealing.
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I bought up stock on all those big, round, silver, knurled edge, Radio Shack knobs when stores were closing around here. I probably have 30-40 of them just sitting here. I see they are sold out online.
I'll gladly ship you a few if you want to PM me your address. (if that's the look you're going for)
https://www.radioshack.com/products/radioshack-silver-tone-knurled-knob (https://www.radioshack.com/products/radioshack-silver-tone-knurled-knob)
You can even save a couple for your next "last" amp :icon_biggrin:
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We should get together Shooter
I have enough black n chrome to make you a full set, the RS diamonds also :laugh:
next time I head south i'll load them with some MI craft beer n some home-grown n PM you :icon_biggrin:
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I've updated the schematic with a couple notes and all my measured voltages. Stole some knobs. Now to straighten out that wiring. Maybe by the end of the week I'll be playing Whole Lotta Love! :laugh:
http://sluckeyamps.com/supro/supro.pdf (http://sluckeyamps.com/supro/supro.pdf)
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Thanks Steve for the awesome photo's and resources.
Can someone please check my math? I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph. In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k). Plate max dissipation is 12W, B+ 350V.
So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A). Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point. 100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor. This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result). Yes?
This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve. And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve.
Am I understanding this correctly? Have I drawn the load lines correctly? I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?
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Very tidy.
Soundbytes?
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Thanks Steve for the awesome photo's and resources.
Can someone please check my math? I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph. In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k). Plate max dissipation is 12W, B+ 350V.
So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A). Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point. 100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor. This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result). Yes?
This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve. And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve.
Am I understanding this correctly? Have I drawn the load lines correctly? I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?
If I'm understanding right, you've just forgotten to divide your pDiss by 2 tubes. Your data sheet is probably showing for 1 tube.
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I got a full set of knobs, tidied up the wiring a bit, and took a few more pics. I still don't have a good idea what this amp really sounds like other than it works as expected and is pretty quiet. Maybe by this weekend my blisters will be healed enough to try some loud guitar. I'll let you know if this amp makes me sound like Jimmy Page! :laugh:
(http://sluckeyamps.com/supro/supro_01.jpg)
(http://sluckeyamps.com/supro/supro_03.jpg)
(http://sluckeyamps.com/supro/supro_02.jpg)
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Beautiful pics!
Now, if I could only get the picture of you soldering in your bathing suit out of my head.... :help: :BangHead:
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Gimme your cell number and I'll send you a selfie! :l2:
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That is just downright purdy! I GOT BLISTERS ON MY FINGERS!
I have not has any dinner!
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Beautiful chassis! Any plans for cabinet? Combo? Head?
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No plans for a cab. It's done. Did you find a switch? Digikey, Mouser, and eBay have the one I used.
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Thanks for reponding John. I don't understand your comment. I've followed the method outlined by Merlin on his website for drawing load lines http://valvewizard.co.uk/pp.html (http://valvewizard.co.uk/pp.html) there's no mention of dividing max power dissipation by the number of tubes used.
Thanks Steve for the awesome photo's and resources.
Can someone please check my math? I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph. In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k). Plate max dissipation is 12W, B+ 350V.
So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A). Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point. 100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor. This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result). Yes?
This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve. And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve.
Am I understanding this correctly? Have I drawn the load lines correctly? I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?
If I'm understanding right, you've just forgotten to divide your pDiss by 2 tubes. Your data sheet is probably showing for 1 tube.
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Nice knobs!
Watching you build is inspirational!
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Inspirational or just Luckey? Thats so punny.
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Steve,
Absolutely bee u teeful. First class amp porn! Will there be sound clips?
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Sorry, no sound clips. I don't have any recording equipment.
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Found the switch locally as well as the 500KL pot with switch. I used to pretty much be able to buy everything I needed from this place, but the lady who ran it for years finally retired and sold it. The new owner is cool, but the stock of things useful to tube amp building has dwindled to almost nothing. What power tubes are you running there? I can't tell from the pics. Thanks again for documenting this build! Very cool layout
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Beautiful work, Steve! You're inspiring me to get going on my Ampeg build.
Now, if I could only get the picture of you soldering in your bathing suit out of my head...
Almost spit coffee through my nose :l3: Wonder how this would sound through a Supro:
https://www.youtube.com/watch?v=OOgd9hitEAE (https://www.youtube.com/watch?v=OOgd9hitEAE)
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@CraigB, are you going to build this amp? BTW, a 1M with switch works just fine for the Intensity pot. I'm running EH 6973 output tubes.
@Sonny, I think that would sound good through any amp! :icon_biggrin:
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@Steve - I'm gonna build it. Ever since the Gretsch rebuild, I've wanted to do one of those, or the Supro. The trem on that Gretsch was one of the best I've ever heard, but it didn't have a depth control. Dang, that's been like ten years ago, so a little slow to get around to it, to say the least. :icon_biggrin:
I've run across a couple negative internet comments about the EH 6973, but I am paying no mind to that whatsoever. I've never had any problems with EH tubes not sounding good or being reliable. I'm pretty sure that's what the new production Supros must come with. So there to the naysayers. Spend your money freely.
And if you don't mind, I will be using your excellent layout, spaced a little different to allow for the size of Mallory 150 caps. Hammond 16x8x3 should work since I won't have a PT cutout. Using Heyboer replacement iron.
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I'll be interested to see your project. Others will too. I don't think you will have to change the board to fit the M-150s.
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Sorry, no sound clips. I don't have any recording equipment.
Oh Well.
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@CraigB, I don't know if you are committed to a particular chassis, but this project will easily fit into a 12.5 x 6.5 x 2.5 chassis, just like the chassis I used on my 6V6Plexi, L'il Maggie, and Dual Lite. And since you will be using a standup PT, you'll have even more room than I had in those projects.
I would have used the small chassis but I had a 17" chassis that I needed to use up. Anyhow, just a thought.
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♫ Duh-duh duh-duh duh! ♪
Finally had a chance to crank this amp. That early LZ sound is definitely there but at ear bleeding volume. So far I've tried a Celestion Blue, Weber California, and a 2x12 cab loaded with Celestion Heritage G12H(55) and Heritage G12H(75). The 2x12 sounds best to me. I plan to try some Jensen and Eminence speakers soon.
At moderate sound level the amp has an aggressive sound with a very noticeable compression. A good sound for most of the stuff I try to play. The sound cleans up a lot just by rolling the guitar volume back a bit. Even at low levels there is still a bit of compression. Wish I could describe the sound better but my ears just don't work well so I'm not sure my description is very meaningful.
The tremolo circuit actually modulates the gain of the first preamp tube. Very smooth and there's plenty of intensity and the speed range is good. I like it a lot better than the trem circuits that modulate the output tube bias or the typical neon/LDR roach.
Running both channels at the same time allows a much better range of tone settings. This will be the default setting for me.
Although I can now cover the opening to "Whole Lotta Love" it still doesn't quite sound like Jimmy. Probably just need a new set of strings! :laugh:
♫ Duh-duh duh-duh duh! ♪
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Yet another great build Steve. I'd love to hear it.
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♫ Duh-duh duh-duh duh! ♪
Finally had a chance to crank this amp. That early LZ sound is definitely there but at ear bleeding volume. So far I've tried a Celestion Blue, Weber California, and a 2x12 cab loaded with Celestion Heritage G12H(55) and Heritage G12H(75). The 2x12 sounds best to me. I plan to try some Jensen and Eminence speakers soon.
At moderate sound level the amp has an aggressive sound with a very noticeable compression. A good sound for most of the stuff I try to play. The sound cleans up a lot just by rolling the guitar volume back a bit. Even at low levels there is still a bit of compression. Wish I could describe the sound better but my ears just don't work well so I'm not sure my description is very meaningful.
The tremolo circuit actually modulates the gain of the first preamp tube. Very smooth and there's plenty of intensity and the speed range is good. I like it a lot better than the trem circuits that modulate the output tube bias or the typical neon/LDR roach.
Running both channels at the same time allows a much better range of tone settings. This will be the default setting for me.
Although I can now cover the opening to "Whole Lotta Love" it still doesn't quite sound like Jimmy. Probably just need a new set of strings! :laugh:
♫ Duh-duh duh-duh duh! ♪
New strings and a telecaster would give more bite on the bottom end. If you had your strat so you could run the neck and bridge and the neck blend pot.
Also, a strat is brighter if you are using the tone pot on a tele like seasoned tele players do. Tone knob centered roll up a little to get sparkle, drop back a little and get a nice power chord.
So you are saying to prefer the Celestine loaded SUNN cabinet? I think that is a great cab and I meant to get dimensions on that thing. That hampeg with that cab is really great. Great punch, so I would think the Supro would sound good too.
I believe it is 20percent speakers and 80 cab. I really like that SUNN stuff for build quality.
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The power tubes were idling at 25 watts with the stock 250Ω cathode resistor. I've replaced that with a 470Ω to cool it off a bit at 17.8 watts.
Steve,
I confess I do not get the above math. Even, with cathode res.470R you'll receive approx.19,5W.
Could you expound your calculation, please?
Thanks in advance.
Regards,
Adam
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I assume you used the voltages from my schematic? Did you forget to subtract the cathode voltage from the plate voltage to get the real plate voltage needed for the calculation?
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I assume you used the voltages from my schematic? Did you forget to subtract the cathode voltage from the plate voltage to get the real plate voltage needed for the calculation?
Actually, I've made a silly mistake .Now, I can see that ,I perceived on schematic 374 V instead of 347 :rolleyes:
For now ,it's perfectly ok.
Thank you Steve!
Kind regards,
Adam
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Steve,
Such a clean good looking amp.
Mark
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I had a chance to try some Jensen speakers today... C12N ceramic and P12N alnico. Surprisingly, I prefer the P12N to all the speakers I've tried. Here's my lame attempt at sound clip using cell phone and MP4 to MP3 converter software. Please don't tell Jimmy! :laugh:
http://sluckeyamps.com/supro/test.mp3 (http://sluckeyamps.com/supro/test.mp3)
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All that needs yet is a picture of you in your bathing suit. :laugh:
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I ain't ready to give it all away yet! :l2:
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Can I ask where you got your fuse holder? I don't recall having ever seen one like that. It looks pretty nifty.
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That fuseholder was very common in military/industrial equipment. The twist in cap has a neon bulb in it which will illuminate when the fuse is open. Look in government surplus or industrial electronics supplier catalogs, or eBay. Do not get one of the low voltage holders.
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I was just about to start handing out defensive ass-whoopins for you, like
"he's done 24+ amps and never posted a sound clip, please stop pressuring him.....if he wanted to post a clip he would. Do you think you're the first one to ask?"
..and then you go and post one.
Love it!...I can definitely hear that Zep quality in there.
I'm assuming that was recorded with your Strat?
I agree with Ed that the Tele would be the magic ingredient.
Now, get busy with those other 23+ clips you owe us :wink:
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Recorded with a 50th Anniversary Strat, S1 system engaged, bridge pickup, 6 month old strings, guitar wide open. Straight into amp at about 60% on volume, both channels. Galaxy S5 phone. Recording sounds a littly muddy to me, but it sounds brighter in the shop. I ain't got sharp ears. SG, you can jump in my corner anytime.
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with all that hoopla stuff you used, did you find you dialed a "sweet spot" on the tone knobs then forgot them, or were you tweaking and playing? I stole the tone knob circuit from your build and find there is a narrow range 4-6 that just works well for me and I forget about it once it's dialed? anyway just curious, thx
dave
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Sounds great Steve. Not bad for cell phone. I'm sure the actual in room experience is something else indeed.
Barry
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THANKS for sharing the sound clip! Sounds good.
With respect, Tubenit
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Thanks guys. Shooter, my ears are not good enough to recognize sweet spots anymore. I don't even know how I had the tone set other than one channel was set a little bright and the other channel was set a little dark. Early on I did rotate the tone knobs through the entire range and noted that they went from muddy to way too bright. I set it somewhere in between and then just flipped the strat switch for a tone I liked. The amp is too loud for me when it reaches the distorted sound that you heard. Not too loud for a band, just too loud for me by myself. My dog thought so too. She would not stay in the shop! :icon_biggrin:
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they went from muddy to way too bright.
Thanks Sir, that's what I found also, but somewhere in the middle just worked :laugh:
And my ears are not far behind :laugh:
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Someone's Jimmy Page is showing :) Sounds great!
~Phil
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That's cool Steve! I think I have everything I need to get started. I think my chassis is 16x8x3, so I'll have plenty of room. You mentioned that you'd like to see how the build goes and maybe others would, as well. I'll just ask since this is your thread and you're a forum moderator here, would you like me to add to your thread or start a new one? Thanks!
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This thread is already pretty long and will probably fade away soon. Probably be better to start a new thread. Looking forward to following.
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Sounds good Steve. Phone worked good.
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I just realized that I never posted a link to my Supro webpage. It's mostly the same info found in this thread, but in a more condensed and organized manner.
http://sluckeyamps.com/supro/supro.htm (http://sluckeyamps.com/supro/supro.htm)
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Very nice work!
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Steve,
Very nice job!
Thank you for this project, very much. I also follow this one.
My question is where might I put the effects loop?
My Supro build is with MV, as you instructed me. I will see ,if this works well.
Anyway, I'll give you feedback with success or fail;)
Thank you in advance.
Regards,
Adam
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My question is where might I put the effects loop?
That would have to go between the junction of the 270K channel mixing resistors and V2 pin 2. Whatever you do, be sure that V2 pin 2 has a resistance path to ground, maybe add a dedicated 1M grid leak resistor.
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Thank you Steve, very much.
Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?
Those ones are two times cheaper then 6973. I mean JJ;)
My build is gonna be with 47uf on rectifying as the first cap. That's because, I do not like tube rectifiers. So, I can provide a bigger one.
Is your 22uf cap enough to reduce hum?
Regards,
Adam
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great thread, great build!
Sorry, no sound clips. I don't have any recording equipment.
Ah, so just when you thought you've run out of amps to build, a new door opens. maybe build a couple mic pre's? maybe one with 48V phantom power to a condenser? a small mixing amp with an output to your phone.. later a computer.. later pro gear gates open...
I had a chance to try some Jensen speakers today... C12N ceramic and P12N alnico. Surprisingly, I prefer the P12N to all the speakers I've tried.
The C12N was Jensen's beast at the time, 27oz magnet with a 1.5" voice coil. Used heavily by Leo.. The P12N that it replaced was a much smaller speaker in terms of power handling.
The Valco speaker of choice for the 2x6973's was the more economy minded C12R with a 10oz. magnet and 1" VC. That speaker (or a similar speaker, ill-equipped for bass frequencies) in a cheap -- (ahem, ... "more economy minded"....) small, open back cabinet is part of the key to valco 24. (by '67 the C12R was a ~5oz magnet really only useful for department store or classroom speakers mounted on the wall...)
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Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?
You could do that. I don't know what would happen to the sound. Might just sound like every other 18 watt amp. I wanted the amp to be as close to the real thing as I could get so I stuck with 6973s. They sound different from all my EL84 amps. AES has an 11% off storewide sale right now.
Why don't you like tube rectifiers?
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Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?
Those ones are two times cheaper then 6973. I mean JJ;)
My build is gonna be with 47uf on rectifying as the first cap. That's because, I do not like tube rectifiers. So, I can provide a bigger one.
Is your 22uf cap enough to reduce hum?
I'm with Steve on the EL84's. If you want EL84s, 47uf and SS diode rectifiers in the power supply, you want something that isn't this circuit.
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Why don't you like tube rectifiers?
Because, it means another expense (tube+socket+space+labour), bigger transformer, filtering caps limitation.
Also, no sonic influence, IMO.
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I don't know what would happen to the sound. Might just sound like every other 18 watt amp. I wanted the amp to be as close to the real thing as I could get so I stuck with 6973s. They sound different from all my EL84 amps. AES has an 11% off storewide sale right now.
Yes, you might be right for above. It sounds wise.
Anyway, I am pretty close with my build, so eventual success will draw further path...
Regards,
Adam
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Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.
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great thread, great build!
Sorry, no sound clips. I don't have any recording equipment.
Ah, so just when you thought you've run out of amps to build, a new door opens. maybe build a couple mic pre's? maybe one with 48V phantom power to a condenser? a small mixing amp with an output to your phone.. later a computer.. later pro gear gates open...
I had a chance to try some Jensen speakers today... C12N ceramic and P12N alnico. Surprisingly, I prefer the P12N to all the speakers I've tried.
The C12N was Jensen's beast at the time, 27oz magnet with a 1.5" voice coil. Used heavily by Leo.. The P12N that it replaced was a much smaller speaker in terms of power handling.
The Valco speaker of choice for the 2x6973's was the more economy minded C12R with a 10oz. magnet and 1" VC. That speaker (or a similar speaker, ill-equipped for bass frequencies) in a cheap -- (ahem, ... "more economy minded"....) small, open back cabinet is part of the key to valco 24. (by '67 the C12R was a ~5oz magnet really only useful for department store or classroom speakers mounted on the wall...)
This is why I'm thinking of going with the WGS G12Q. It's got a 1" coil and light magnet. So it should pair up nicely.
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Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.
Steve,
Yesterday, I fired up my Supro with 6973 onboard.
Plate voltage is up to 350V (energetic network fluctuations at my place). On cathode I've got 25,2 V. Cathode resistor 360R. So, it means that output power is appox.22W.
Nevertheless above, I feel that the amp is too weak. This is my first built with that type of PI. Maybe, the power is not as big as in the long tail pair PI?
MV seems to work fine. I provided stereo 500kA pot as you suggested. The only difference is I applied two 2,2M resistors across both pots. Maybe ,I should change the MV pot(s) value?!
Thank you in advance.
Regards,
Adam
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I don't think mine is as loud as my Marshall 18 watt. But I don't consider it weak sounding either. This is my first experience with the paraphase inverter too. Could be a factor.
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This is my first experience with the paraphase inverter too. Could be a factor.
So is mine;)
Today ,I just bypassed MV and that is the amp's final state.
This amp is not the powerful one. So, I also consider it as an experience.
If I am asked to build another one, I'll do it with poliester caps. My favourite polypropylene are too dark even to my taste.
Therefore, I suggest the other builders to provide those caps, IMO.
Thank you Steve, very much.
Best regards,
Adam
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Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.
Steve,
Yesterday, I fired up my Supro with 6973 onboard.
Plate voltage is up to 350V (energetic network fluctuations at my place). On cathode I've got 25,2 V. Cathode resistor 360R. So, it means that output power is appox.22W.
Nevertheless above, I feel that the amp is too weak. This is my first built with that type of PI. Maybe, the power is not as big as in the long tail pair PI?
MV seems to work fine. I provided stereo 500kA pot as you suggested. The only difference is I applied two 2,2M resistors across both pots. Maybe ,I should change the MV pot(s) value?!
Thank you in advance.
Regards,
Adam
The paraphase inverter can actually supply more gain than the LTP or cathodyne. The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides. The LTP provides a distinctive tone that the other inverters don't and many people are used to that, so when a different inverter is used, they find they are missing that tonal thing that the LTP does.
The 6973 is based on the 6V6, though it comes in a 9 pin bottle and has higher voltage capability. The 6V6 isn't known for it's highs, so perhaps the 6973 is similar...I haven't tried that particular tube in a build yet so I don't know firsthand. Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.
Greg
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The 6973 is based on the 6V6
6973 is up-rated 6CZ5.
--pete
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The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides...
Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.
Thank you Greg, very much. You knew, what I was asking for...
Yes, I am afraid that the amp is too dark as It should be as a Supro replica. I prefere Fendery tones. So, for me the amp is ok. But, it has been built for my friend, who expects that characteristic highs and grittiness.
Could you explain me what is floating paraphase and how to tweak the amp to be moore close to 6424 tone, please?
Thank you in advance.
Regards,
Adam
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The 6973 is based on the 6V6
6973 is up-rated 6CZ5.
--pete
Yes it is directly, but it can be traced back to the 6V6. There was an article in Vacuum Tube Valley issue 15 about it and other 9 pin "dumpster" tubes.
Greg
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The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides...
Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.
Thank you Greg, very much. You knew, what I was asking for...
Yes, I am afraid that the amp is too dark as It should be as a Supro replica. I prefere Fendery tones. So, for me the amp is ok. But, it has been built for my friend, who expects that characteristic highs and grittiness.
Could you explain me what is floating paraphase and how to tweak the amp to be moore close to 6424 tone, please?
Thank you in advance.
Regards,
Adam
If you want the raw Supro tone you need to stay with the un-balanced paraphase as they used. You can adjust the value of the resistors in the circuit to get more or less balance out of the phase inverter, but if it balances too well then you lose some of the Supro character. That said, it might still sound good with the floating paraphase, or at least have some of what you are looking for. I haven't studied the 6424 circuit in detail and don't have time to do so right now. You will never get the Fenderey shimmer and cleanness out of a Supro derived circuit though without changing a lot of things. They do lots of things but they won't do that Fender sound.
Here is a link to the floating paraphase circuit on Merlin's site:
http://www.valvewizard.co.uk/paraphase.html (http://www.valvewizard.co.uk/paraphase.html)
You can also study the Vox AC100 schematic as it used a floating paraphase with a 12AU7.
Greg
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If you want the raw Supro tone you need to stay with the un-balanced paraphase as they used. You can adjust the value of the resistors in the circuit to get more or less balance out of the phase inverter, but if it balances too well then you lose some of the Supro character. That said, it might still sound good with the floating paraphase, or at least have some of what you are looking for. I haven't studied the 6424 circuit in detail and don't have time to do so right now. You will never get the Fenderey shimmer and cleanness out of a Supro derived circuit though without changing a lot of things. They do lots of things but they won't do that Fender sound.
Thank you for above, very much.
Actually, I seems in acc. what you've mentioned, I have well balanced circuit, because I feel I did not received raw Supro character basis its schematic. It is more Fendery then Supro now. Amp sounds smooth and warm like a hell;) Both channels stay cleaned up to 80-85% of their volume.
So, the issue is how to get highs and grittiness of Supro?!
Any suggestions?
I applied polypropylene caps, mainly. Maybe, that is the reason of smoothness and warmness?
Regards,
Adam
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Which PT and OT did you use? Post voltages for each power supply node and all tube pins.
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1) Is the switch on the intensity pot (SW-2) needed? It seems like you could use the foot switch and intensity pot to control the trem, but do you get any ticking or thumping noises if not using SW-2?
A front panel switch (whether on the pot or a separate toggle switch) is not strictly needed but I think it's very useful. But if you will always have a footswitch plugged in, it becomes redundant. Removing the switch will not cause any ticking/thumping noises.
Is your question based on the fact that a 500K-L pot with push/pull switch is difficult or impossible to find? If so, I assure you that a 1M-A pot with push/pull switch is easy to find and works great. The 1M pot will actually give you a stronger tremolo too.
2) Instead of the input jack switch to choose channel 1 or 2 or both, would running the shielded cable and 2.2K resistor to V1 pin 2 and a jumper between pins 2 and 7 give the same variety? Just use the volume pots to control whether you use a single channel or both together?
That'll work just fine. Since I prefer to run both channels all the time I would probably do just as you say if I were going to build another for myself. I think most people would like the switch.
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Deleted
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Thank you for above, very much.
Actually, I seems in acc. what you've mentioned, I have well balanced circuit, because I feel I did not received raw Supro character basis its schematic. It is more Fendery then Supro now. Amp sounds smooth and warm like a hell;) Both channels stay cleaned up to 80-85% of their volume.
So, the issue is how to get highs and grittiness of Supro?!
Any suggestions?
I applied polypropylene caps, mainly. Maybe, that is the reason of smoothness and warmness?
Regards,
Adam
A lot of the Supro sound is the lack of negative feedback, and the unbalanced phase inverter. Some of it is the use of ceramic caps. Obviously the voltages would matter as those determine the power output of the amp (along with the impedance of the transformer in relation to the tubes), but also the headroom and gain of each stage in relation to each other. You can deviate from standard values for the dropping resistors and adjust the voltages of each stage in relation to each other. If you have a scope you can adjust so the power amp distorts first, followed by the phase inverter, then the next stage, etc., to the front of the amp. This is called gain scheduling and you can tailor the amp to distort the way you want by adjusting the operating voltage of each stage. This changes the headroom and gain level of each stage. To make it work best, each stage should have it's own filtering node and dropping resistor. Assuming you used appropriate transformers to duplicate the primary impedance and voltages of the original, then you are left with the balance of the phase inverter and the caps you are using. Considering the original resistors used likely had a 20% tolerance, then you can play with the resistors in the phase inverter circuit to purposely unbalance it and get some of the Supro grit. I forget right now which specific resistors in the phase inverter circuit should be adjusted, but it is really only two of them in relation to each other to get the balance or unbalance, one in each side of the inverter, though I suppose you could play with all them in that specific area of the circuit within 20% of their value now and see what you get. The ceramic caps also contribute to the grittiness of the Supros....they aren't as "perfect" of a cap in comparison to polypropylene but that isn't the point of these amps.
Greg
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Which PT and OT did you use? Post voltages for each power supply node and all tube pins.
Steve,
Here are measured voltages:
V1 - input -
1-188V
6-104V
3-2,44V
8-1,12V
V2-PI-
1-138V
6-165V
3-1,12V
8-1,67V
V3 - tremolo - I didn't ground it for measurement, so...
1-284V
6-145-158V,
Power tubes both-
1-8 - 340V
9-352V
7-25,2V
Power supply 230V.
Nod 1-354V
Nod 2-341V
Nod 3 - not measured;)
Rectifier - Graetz bridge.
Filament - 6,6V AC
OT by myself - primary 7,5K, secondary 4,8,16.
Regards,
Adam
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Your voltages look about the same as mine. Maybe the amp is working correctly and doing all it's supposed to do? I don't consider this amp to have a bright sound, more of a woody tone to me. The Jensen P12N alnico I'm using is fairly bright. Does your amp sound anything like the sound clip on my website? That was made with a cell phone and with the volume turned up pretty loud. Much too loud to talk over.
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This is interesting. FWIW, I find mine to have plenty of brightness, not piercing brightness, but certainly not muddy, even with the tone on lower settings. I think the lower volume clean tone and natural compression, being very pedal friendly and killer trem are what make the circuit shine. Channel 2 does have more of a woody midrange than Channel 1. Using mine with a 12" 8ohm Eminence George Allessandro speaker in an open back cab and an assortment of single coil and humbucker equipped guitars.
Steve, I have tried to get a decent recording with an iPhone and it clips awful. I even tried placing the phone in the other room with the door open and just sounds awful. Did you use any special app or just the voice memo recorder? Your recording sounds pretty good
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Steve, I have tried to get a decent recording with an iPhone and it clips awful.
You gotta move up to the Galaxy! :icon_biggrin:
Seriously, I just laid my S5 face down about two feet in front of the speaker and let it rip. The S5 records a MP4 video that's too big to post here even though the video was all black. I used a software program to extract the audio and save as a much smaller MP3 file. The original MP4 still on my phone sounds brighter than the MP3 posted on my website. But the grind is there on both.
I can't say about the audio quality from an IPhone, but the quality of pictures from my old Galaxy S5 is waaay above the pic quality of my wife's IPhone 6.
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Ah hah, the Samsung vs. iPhone debate continues :icon_biggrin: well, no debate here...I'm stuck with a 6S for another year and a half - no likey!
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I love my Android phone, mines the LG G6, and I gave up on apples back on version 3 or 4, they lock you in so tightly they never let go and you need to fight to get away from them :P
I'm definitely amazed at how well that sound came out on a phone, for sure.
~Phil
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Someone is requesting Sluckey's Supro board as shown in Steve's PDF file
I can make them as an eyelet or turret board
You can use the price calculator link below to submit the info
http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php (http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php)
I already have the drilling info for this board on file so there is no extra charge for not having a .dxf file
The board is 3.125 inches tall x 8.5 inches long
There are 56 terminal holes
Note that I don't drill wire holes or mounting holes, only the 56 terminal holes
Pick the board type and terminal type in the calculator
This is what it looks like with terminal holes only
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Only $22.19 for a black turret board. Shit! I ain't never gonna build another board. From now on you can do my boards Doug. :icon_biggrin:
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Yes, well the first one would be way more expensive :icon_biggrin:
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I'll just take the second one. :l2:
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Yeah, that is a great deal! Thanks Doug!
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The prices would vary by material type, color and terminal type
The calculator sends me the specs/info for the board you want made
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You do really nice work Steve and this amp endeavor is no exception. I will join others saying thank you for the documentation of this project, making it available to all, and for all the help you selflessly give to any who enter here.
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I have the drilling file already set up for this board
If anyone wants one, fill out the calculator program first here
http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php (http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php)
Pick yes that you have a cad file so there will not be an extra charge
Pick the material type, color and terminal type
The board is 8.5 inches long
Fill out a note that says
Sluckeys 6424 Supro and I will know to use the drilling file I have already created
If you have other parts you need, go to my shopping cart and add a note to your order to add this custom board after you have filled out the board price calculator form
If you do not need any other parts, just email me to order the board after you have submitting the board price calculation form
Look at the screen shot below to see how I filled out the calculator form
(http://el34world.com/Forum/Files/Sluckeys_6424_Supro.png)