Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: lego4040 on September 03, 2014, 02:54:40 pm
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So Id like to build my 3rd amp from this site and Its going to be Dougs Stout with the black board. I want to use my 5F2 chassis in my 12" combo cab. If I loose the tube rectifier I have the spot for the second EL84. I have three pots which will allow me to use the gain pot mod(which says master on this chassis. I have the DPDT bright switch which I can use for the gain switch mod or maybe some cap mod. This chassis is larger then Dougs will be and offer me some room. I already have the Allen TP25 PT in it and the small choke, I will need a new OT tho, the Allen OT11c will not work if Im correct. Here are some shots of what I have to work with and chassis I will gut for the most part
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Here is the circuit for this amp
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That cab is beautiful!!!!!
Did you make? What kind of wood is it?
Brad :icon_biggrin:
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Believe it or not that's Poplar. John Lyons who is a master and a gentleman owns http://basicaudio.net (http://basicaudio.net). He makes wicked pedals from the ground up and he made my cab. I don't know if he still does since the last time I asked he was just to busy. When he picked this wood he explained that poplar is greenish but when left in the sun for long times it turns redish. So go get cheap priced poplar and let it tan in the sun for some amazing results
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That cab is beautiful! It looks great!
If that is poplar, it sure looks different then the poplar in my area of North Carolina. I've cut down some 90+ ft tall poplars out of my back yard. The wood is very green and/or yellowish looking.
With respect, Tubenit
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Tubenit that's is exactly where John is from and the color it was when he got it. He let it suntan for probably two weeks or so
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So my first quest in using this chassis over is removing the tube rectifier and using it for the second EL84. I was thinking about going to solid state(?) and bolting the rectifier to side off chassis where that giant 25 watt power resistor is. The chassis can serve as a heatsink for the rectifier & its out of the way(Now I don't know if thats a good idea or not but I'm just thinking aloud). Since I'm not using the 5v heater taps for tube heaters that will take some load off of PT. I just need to know If I need to change anything, add a cap or resistor for noise, etc. I was reading some of Merlin's work on that and looked in the library here but I couldn't find anything on changing tube to solid state. :anyone:
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Have you considered just selling the 5F2 chassis on eBay and starting with a clean slate?
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Yes but shes my baby, first amp I built. The stout board will fit right in and once I pull chassis out I can really measure things out. I dont have a problem with not using the 5Y3 but I want to make sure I can do that and what I might need to do to it. Isnt that what you did with the Revibe
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I would just put the B+ from solid state to the choke
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Hmmm, ordering parts from Site now but the only .68uf cap here is 250V. BOM calls for a 400-600V. You have any laying around Doug that might not be on site :icon_biggrin: that I can buy from ya
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I see the other BOM has it at 250v, nevermind :icon_biggrin:
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That's a cathode bypass cap in the preamp. Probably never gonna see more than two volts.
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:thumbsup:thanks Steve, seems I've lost track of time :occasion14: nothing like hanging with the deep Europeans from The Czech Republic and proving that New Yorkers aren't all DB'S
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Just not fond of the 5F2? Sometimes just something different.
That is a great starting point with the 12" cab. Looks like it is easy to handle. I am going to try that with poplar. I just laid out a 1 x 4. :icon_biggrin:
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Here is the circuit for this amp
Image is too small, can't see the schematic. Is is a 5F2 with a added master?
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Ed it has the added Master and a extra 12ax7 for some umph. This chassis has every thing if need once I rip out that board. I'll convert to a solid state and use that rectifier hole for second EL84. The bright switch will become either the switch for gain stage. The master volume will become the gain pot mod. I already got my shopping cart loaded here, just need some extra cash
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I ordered all my parts today. I got most parts coming from here but I did wind up going with the Classictone OT for this build. I had to hold off on ordering for a little since my wife got laid off last month, thankfully she just went back to work on Monday.
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Ok, I got my chassis gutted to were I need it today. Parts on the way and I'm ready to Rock. So I want to use my matched pair of 6V6's for this project, two reasons, I ave the sockets in chassis to begin with and my wife just got back to work so I gotta watch the $$. I see the grid resistors for the EL84's are 8.2k and the resistors to ground are 470k. On two 6v6 builds I looked at, like these two are less. Im no expert so I gotta ask what I should do. The trainwreck versions here are 5.6k on grid and 220k to bias and the other version has 1.5k on grid and 220k again to bias which would be ground for this build. :help:
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Done some research and I will build amp with Doug's specs and just change tubes to 6v6's(of coarse w correct pin outs
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:happy1: Doug's board and parts came today and now I have something to keep me occupied. I wired the heaters and lamp today, I also tidied up the PT wires. I also realized after I wired up the 8 pins for the 6v6's I had not just one set of matched EL84's but two sets from JJ :BangHead: I have the 9 pin sockets for them but if I want to change them I need those socket adapters ASAP. If I can find some decent metal stock I'll shape two out and change sockets before I go further. I did some reading on 6v6 vs EL84's, the best way for me to describe what I read is what we all know already. Cranked American Blues amps vs Cranked British Rock n Roll
Till tomorrow
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Looks like you are on your way
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I'm aiming to get the board populated today and maybe put into chassis. In the chassis pic there I put foil tape and heat shrink around heater wires. They pass over output jacks and I wanted to try and keep noise out. I did get radio stations with the circuit that was in here from time to time and now understand why grid res are used. I'm still using the 6v6's although I did find two matched pairs of JJ 84's. Maybe next build will be all four :rolleyes: I read an article yesterday on how some amp builders use both the 6v6 pair and EL84 ish pair set up so they can get both the Fender low and fatness along with the British attack. :angel has or can you use one EL84 and one 6v6????? I'd be the test pig and do it on this build
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Believe it or not that's Poplar. John Lyons who is a master and a gentleman owns http://basicaudio.net (http://basicaudio.net). He makes wicked pedals from the ground up and he made my cab. I don't know if he still does since the last time I asked he was just to busy. When he picked this wood he explained that poplar is greenish but when left in the sun for long times it turns redish. So go get cheap priced poplar and let it tan in the sun for some amazing results
I recently finished a closed-back 1x12 speaker cab that I made out of poplar... the stuff you can buy at Home Depot or Lowe's. I stained it "gunstock" and it turned out beautiful as well. The banding effect from the different edge-joined planks adds an interesting dimension to it. I found the poplar cheap and easy to work and most importantly the cabinet sounds great! I'm going to build a head cabinet for my new 18-watt build to match it this week, hopefully starting tomorrow.
I didn't know about the "suntan trick" I'll have to try that on my next build.
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I need to get some poplar, I've been putting my wood tools together too. Here's my stout as of tonight
And I've made the cap look vintage. I peeled plastic off, rolled brown paper and schellac.
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Ok, I got my chassis gutted to were I need it today. Parts on the way and I'm ready to Rock. So I want to use my matched pair of 6V6's for this project, two reasons, I ave the sockets in chassis to begin with and my wife just got back to work so I gotta watch the $$. I see the grid resistors for the EL84's are 8.2k and the resistors to ground are 470k. On two 6v6 builds I looked at, like these two are less. Im no expert so I gotta ask what I should do. The trainwreck versions here are 5.6k on grid and 220k to bias and the other version has 1.5k on grid and 220k again to bias which would be ground for this build. :help:
I did a 6V6 build a few months ago and used 100k to bias and 5k6 grids. It's basically a Fender Deluxe clone.
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If a 350-0-350 is to high could I drop it by changing the 130ohm 10 watt to say 330ohm 25watt. This was in my amp that was using this PT. Here is power resistor and the board in chassis so I can look at where main cap will go. Looks like main cap is going on top outside chassis
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If a 350-0-350 is to high could I drop it by changing the 130ohm 10 watt to say 330ohm 25watt.
No. That 130Ω resistor is the cathode resistor for the EL84s. If you will be using 6V6s that will need to be 250Ω or higher. That resistor is not used to drop B+. It is used to bias the output tubes.
That 350-0-350 PT will put out 495vdc unloaded. Since you will be using a SS rectifier you can expect that to be pretty high even when loaded. How high? Can't say. That depends a lot on the internal resistance of your PT. You would normally put a dropping resistor between the rectifier and first filter cap to drop B+. My preferred method to drop B+ is to use the correct PT to begin with.
Give us all the info on that PT. Is it an Allen? If so, which one? Was it used in your 5F2? If so, what was the loaded B+ in that amp?
Edit... I see from your original post that you have the Allen TP25 PT. According to Allen's website, the TP25 is rated for 310-0-310 @ 150mA. That PT will be fine for a cathode biased 6V6 PP amp. Still need to use a 250Ω 10W cathode resistor rather than 130Ω 10W.
So, where did this 350-0-350 come from?
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It's the Allen TP25: Upgrade Power Transformer for BF/SF Champ™, VibroChamp™, Bronco™, and Princeton™. 310V-0-310V @ 150ma, 6.3V at 4.5A, 5V at 2A. 50V bias tap, center-tapped heater winding and internal hum shield brought out to a lead for grounding. 2" by 2-1/2" mounting centers, 5.1lbs. Unit is approximately 1" taller than a stock transformer. Supports the use of both 6L6 and EL34 power tubes (with proper socket wiring). Now featuring M-6 grain oriented lamination steel for cooler operation. I got 350-0-350 when I plugged in the tranny not hooked up to anything by chassis. So I will need to step up that bias to 250ohm. I new it was for Biasing but wondered if that would work
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The schem I have for the Allen amp I built doesn't give any voltage readings either.
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The schem I have for the Allen amp I built doesn't give any voltage readings either.
And you didn't record any voltage readings when you built it, right? Or just before you scrapped it for the stout build either?
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I didn't take any readings back then, first amp I ever built and wasn't poking around in there. I was going to before I took it apart but was to anxious to start new project
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I think you'll be OK with that PT. Looks like you have a STBY switch? If you need to drop B+ some maybe you could do my 'Standby Plus' mod like on the AC15. Otherwise, reserve a place to put a big dropping resistor just in case.
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Will do and look for your drop down link
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Found it, what about the Zener diode trick off the center tap to ground for a few volt dropage
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That'll work too, although it's not my preferred method. Just put all the voltage dropping options on the back burner until you build the amp. You may not need them at all.
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OT came today :icon_biggrin: I waited outside for the mailman to come so I wouldn't miss him
Also some more parts from Doug coming soon
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So I got some work done and once my last of parts come in I can finish up. The OT is in the holes that was in chassis(factory) but it's same way as PT, will I have issues? Not sure were cap is gonna go, I can squeeze it between chassis and PT underneath and actually fit cap next to it. It will keep wires short as possible too. Now I have the DPDT switch doing nothing :dontknow: maybe some cap mod possible? I am adding the gain pot also
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Holy smokes, what kind of power tranny is that and why is it 3 times taller than a normal PT?
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That's the AllenAmp PT and I believe Heyboer is making all their trannies. It's a beast isn't it. It's what came with the amp kit when I first built his AllenAmp. It's the TP25, his specs show 320-0-320. I have 350-0-350 but no load on it. Your parts came in today so I'll wire up the rectifier and see what I get on the DC. I also realized I didn't order a 6v6 from you the other day. I need the one I put in the revibe( it's from a matched GE NOS set) that I will stuff in this build
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It's Allen Amps TP25 power transformer. Website says it rated for 310-0-310 @ 150mA. I have one in my Harvard 5F10. It is thick isn't it? Here's mine and the PT it replaced. Thankfully it was a drop in replacement.
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So I hooked up my SS rectifier and I got 630VDC, to much?
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So I hooked up my SS rectifier and I got 630VDC, to much?
The only way to get 630vdc out of that 310-0-310 PT is to use a bridge rectifier (or some doubler). Don't do that! You'll kill your filter caps before you even put a tube in it.
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:sad2:
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The only way to get 630vdc out of that 310-0-310 PT is to use a bridge rectifier (or some doubler). Don't do that!
Let me be more specific with that statement. What I should have said is you cannot use a full wave bridge CIRCUIT. But you can use a bridge rectifier block as a conventional full wave rectifier simply by not connecting the negative terminal to anything. Connect the other three terminals as usual and connect the HT CT to ground just as it was when you were feeding a tube rectifier.
Those little 1" square blocks usually mount with a single screw and provide a neat convenient way to connect wires, without needing additional terminal strips or standoffs.
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:huh:I just pulled it out too which will take two seconds to put back. So I wouldn't hook up the negative on the DC side of rectifier your saying? I was reading Merlin's stuff on full and half wave rectifiers, will have to go back. I hooked up the Tube rectifier on a temp rig and this is the DC I got from it. I'll read up on the differences so you won't have to explain. If I go to tube I got to put it next to OT on top, then I have a heat issue since this cab isn't vented on top
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I was reading Merlin's stuff on full and half wave rectifiers, will have to go back.
Both rectifiers we are discussing are FULL WAVE rectifiers. The typical single diode bias rectifier that we are so familiar with is an example of a HALF WAVE rectifier.
Rather than punch a hole for a rectifier tube, I'd just go ahead and use the bridge block without connecting the negative terminal. It's not gonna make much difference in a cathode biased amp.
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:thumbsup:
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Back in, negative DC on the SS CAPPED and not connected to anything. Next is the multiple cap
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I can't see anything in the tiny pics you are posting in this thread. Doug's requested size limit is...
Please reduce your images to a max of 1024 pixels wide and 800kb or smaller
So, take the size on up to say 1024 x 768. And shine a light on the chassis! Then we will be able to enjoy your build much more. And no one will be mad at you for pic size.
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Okie dokie on pics. I got multicap in as well, maybe tomorrow I can finish. I have some wires to sockets, pots & the gain pot, oh I want to wire the 1ohms in so I can read the tubes.
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Much better. But your aspect ratio has changed from the original pic and that distorts the true pic. You misinterpreted Doug's limitations. "1024 pixels wide and 800kb" does not mean 1024 pixels wide by 800 pixels high. It means 1024 wide and keep the file size below 800KB (kilobytes). When you resize or crop your pictures you can specify 1024 as the width, but don't specify a height. Instead, keep the original aspect ratio. Then resistors will not look very skinny or fat. They will look just like the original pic, only smaller.
If you ever resize a pic of your wife and change the aspect ratio such as the width is much greater than the height, she'll explain it to you in different terms! :icon_biggrin:
Anyhow, now I'm beginning to see what you are doing.
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If you ever resize a pic of your wife and change the aspect ratio such as the width is much greater than the height, she'll explain it to you in different terms! :icon_biggrin:
:w2: :l2:
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Ok I hope I read schem correct. I removed the 470k in between .022uf and 47k(V1 P6) and added the 500k pot. That's the yellow and whit wire you see on board and next pot is it wires to pot
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See pic... This is how to replace R14 with a gain pot.
FYI, the red arrow pointing at C6 is the famous Stout error. The bottom end should be connected to ground. Doug won't tell us if the error is intentional. The amp works either way.
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So that gain pot is wired like a volume control. I wired mine like a trimmer resistor, turn clockwise and resistance goes up. Here is how I did it. I reset and pot works correctly, am I wrong? My understanding was that should pot fail it can't go past it's rating
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I fired it up with the poor man variac and all is good. 480vdc on the plates and that's as far as I got, schems didn't have volts readings and I have 6v6's. I ran outta time and left shop. Odd thing is I had no sound when I hooked up guitar but I was expecting that, I gotta go back and check inputs and rest
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480v on the plates. That's gonna be one hot little amp... for a little while!
I really didn't think that little PT would put out that kind of voltage.
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Tisssszzzz, hot little B isnt she :icon_biggrin: I know I have to really look at wiring when I have a period of time. Thanks for the neg ground lift, I can take some readings I'm the afternoon and get them posted
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Deadly hot for those tubes.
I have that same Allen TP25 in my 5F10 Harvard fixed bias 6v6 amp. I only have 387V on the plates. I believe you may still have a dangerous B+ problem, or your meter is lying.
What is a poor man's variac and do you have 480v on the plate while using it? I hope you're not talking about a household lamp dimmer?
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Not a dimmer, oh no. It's a current limiter actually, light bulb thingy. When you power up it goes dim, if it stays bright then you have a wiring error in amp. I figured it was still to much, back to drawing board
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Are you sure about the wiring of that bridge? PT red wires go to the AC terminals. Plus terminal connects to filter caps. Negative terminal connects to nothing. PT Red/Yellow wire connects to chassis. PT Orange is not used in this amp. PT Yellow wires are not used.
I suppose if your PT is putting out 350-0-350 (unloaded) AC to the rectifier, then your unloaded B+ would be 495V. I would also expect that to drop considerably when the tubes warm up. It may all be correct. If so, you will likely need that 300Ω resistor between the bridge positive terminal and the first filter cap.
I just checked the voltages in my Harvard. The TP25 is delivering 345-0-345 to a NOS 5Y3 tube. Voltage at the first filter cap is 390V. The amp is fully warmed up and loaded for these readings.
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Ok Steve I have my PT wired like this: red pair to bridge, red/yellow to chassis ground. Red/green not used. Orange is to chassis ground( you weren't using yours) should I lift it off and cap? Green pair to lamp/ heaters. Green/ yellow to chassis ground. Yellow pair not used since I put in solid state. I had this in amp in amp with this PT before. I will put this between DC positive and 40uf cap and see where it drops to. Also verified I have input jacks wired wrong, need to fix
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IMHO, you have the wrong PT for this application. see PSUD2 plots below. i estimated the load currents. the 367V is estimated NL voltage of the B+ winding. the 115ohm source Z is based on readings that steve provided. last sim is with the 330ohm resistor inserted. the load current is an estimate.
--pete
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Steve I added the 330ohm between bridge and cap, didn't really do much. I got 470 on the plates, A:470 B:470 C:419 D:410. I am gonna either have to buy different tranny or go to tube rectifier. I don't want to have to buy anything else for this project. Tube rec next. Will post results
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is that with tubes installed?
--pete
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Yeah, I just disconnected the solid state and hooked up the tube rectifier. I got the plates down 450 and the abcd's down as well. I guess I'm getting a new PT
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Readings with tube
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Would anyone know the Hammond transformer that would work here? I can get it thru work and order two. Use it for another project.
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The 290CAX is a good choice, electrically speaking. Use the 275-0-275 taps. Compare the physical dimensions to your TP25 to see if it will fit the existing holes.
http://www.hammondmfg.com/pdf/EDB290CAX.pdf (http://www.hammondmfg.com/pdf/EDB290CAX.pdf)
The PT in your AC-15 is another good choice if you don't mind covering the big cutout in your chassis.
It's not Hammond, but Doug's 18W PT is another good choice if it fits the chassis. The physical dimensions are listed.
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I can get these for nothing from my supplier. I can't do it all the time but I got a ok today
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Ordered two Hammonds from my supplier. Gonna get other one out monday
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I measured my TP25 this morning. Looks like that 290CAX should just drop in.
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Thanks for doing that Steve, I'll take the PT out and reinstall the bridge rectifier. What would I use that PT for then. Maybe I put it on the Buy sell trade page
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What does Allen say it's for?
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Thanks for doing that Steve, I'll take the PT out and reinstall the bridge rectifier. What would I use that PT for then. Maybe I put it on the Buy sell trade page
same thing. drop in a pair of 5881 or EL34 w/ a 4K load: vibrolux OT. more power! ugh! ugh! ugh!
--pete
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Well the PT came with his 5F1+ kit. I was running the amp with a 5881 and two 12AX7. But I'm down with Steve's next build if he does it, a tweed Princeton Reverb!! I'll build that in a heartbeat. Maybe I can use it there
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that PT was designed to kick the tweed champ/princeton/harward up a notch with a 6L6GC/EL34/5881 & tube recto. allen sells the OT compliment: the TO11C/TO11S
--pete
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I have the TO11 and the choke that comes with that set. I put the TO11 in a box and on the shelf for later usage. I was putting out about 12 watts with his 5f1+. When you mentioned 4k load, you were referring to the OT for the Vibrolux? I'm still a newbie with all this amp tech stuff
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I just looked at your voltage chart! :huh:
You either have a bad meter, are measuring incorrectly, or there are some serious wiring errors in that amp. Please recheck. Whenever you get some believable voltage readings on ALL tube pins, your high B+ may be acceptable also.
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Well a wiring error is believable but it did check out with the current limit bulb tester. I can order those washer thingies Doug was making on his 3d printer if he has them, so I can put the EL's in them that the build calls for. Doug you selling those 8pin to 9 pin spacer tube sockets, I'll email him
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EL84s will not hold up to the kind of voltages you are reporting. Please just recheck and post voltage readings for all tube pins. Don't really need a picture. Just type the numbers.
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Many of the other voltages are way off also, like the readings of about 300VDC on the preamp cathodes - this should be about 2 volts!
Please be careful - when I see voltage charts like this, I worry that the readings are not being done in a safe manner.
I saw a young man get shocked badly testing a big tube Tek oscilloscope when I was about 20 years old. He lost his arm. That's why I harp a lot on safety.
This is not to insult anybody - but consider taking those voltage readings again, and make sure your DMM is set on DC Volts, and the Negative lead is connected to circuit common, like the negative side of the power tube cathode bypass cap, or right on the lug of a star ground.
And please put one hand in your pocket whenever probing a live circuit with the other hand. This will eliminate the current pathway through your heart muscle if you get shocked, and it only takes about 100mA to kill you :huh:
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Oh I'm being safe, one hand testing always draining, etc....... I will take PT out, take 6v6 sockets out and find those spacers. I will recheck the board wiring and all. Those volts are to close to the cap 500v ratings and I don't want problems.
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Hmmmmm, I pulled out PT and make a test board. I have 350-0-350 AC, and close to 700 together. when hooked up to bridge I get anywhere from 650-700dc. When I hooked it up to 5y3 I got only 350dc? That ain't right! 350*1.2 should get me around 420. I made sure all connections where right, I may have killed tube rectifier with those high volts, you think it's time for a new one
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Hmmmmm, I pulled out PT and make a test board. I have 350-0-350 AC, and close to 700 together. when hooked up to bridge I get anywhere from 650-700dc. When I hooked it up to 5y3 I got only 350dc? That ain't right! 350*1.2 should get me around 420. I made sure all connections where right, I may have killed tube rectifier with those high volts, you think it's time for a new one
Both of your meter readings are meaningless.
You are measuring voltage wrong on the bridge. Black meter probe needs to connect to the PT center tap which you have connected to a PT bolt. Then positive probe connects to plus terminal on the bridge. ***CONNECT NOTHING TO THE NEGATIVE TERMINAL ON THE BRIDGE***. If I were you I'd just cut the negative lead off flush with the body of the bridge so you will leave it alone. :icon_biggrin:
Same goes for measuring voltage with the tube. Black probe to PT bolt, red probe to pin 8.
One more thing... You don't need a new tube. The voltage from the 5Y3 is not low. You must put a filter cap between pin 8 and that PT bolt before your meter will quit lying to you. Likewise, you need to use a filter cap on the bridge to get a correct meter reading. I suggest putting a 100K to 220K resistor across the filter cap so it will discharge when you unplug the power. Otherwise, that cap will bite you.
EDIT... There's nothing wrong with that PT other than the fact that David Allen advertises it as 310-0-310 but in fact the one he sold me is 345-0-345 and the one he sold you is 350-0-350. That PT is just not a good choice for the Stout.
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Ok Steve here it is once more :icon_biggrin: as per your instructions. Third picture is how I hopefully connected the gain pot, ccw resistance decreases and vise versa. My Free PT is a week from me and I'll gotta give Doug some more business
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Don't you love it when stuff works like you expect it to? :wink:
As for the gain pot... That's the brute force way to do it. It'll work. I showed you the elegant way to do it.
And if you want a fatter sound, here's what I'd do... :icon_biggrin:
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:l2:
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Glad you can recognize my sic humor. You also got the point, right?
Here's the elegant method in layout format...
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Took a second but I got it, on your more elegant way you wouldn't be connecting to the 47k anymore. Reason?
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Look closely. It's still connected to the left end of that 47K.
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Where? The .022uf was in series with the 470k and went up to 47k, it also teed over and went to the .01uf. You wired the pot where the line connects to the .01 but eliminated the wire up to 47k. The wire on right side to the 47k hasn't changed changed. I still haven't had my two cups of coffee so I could be sleeping still
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Fingered it out yet?
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Ooo, Oooo Mr Koter, the gain pot leg 1going to ground
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Good boy Vinnie! You can have an A in 'picture lookin' or two beers for lunch or sleep with Julie tonight. Your choice. :icon_biggrin:
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What is the purpose of the "gain pot". Does it lower the gain to get a cleaner signal?
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yes, it lets you dial in voltage input to next stage I believe is how it was explained
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wired as is it keeps the gain stage connected to the top of the pot AC load constant like the 470k r does. now you get to vary how hard you slam the LTPI.
--pete
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Made all my changes, wired as per Steve. Just need to hit send and my parts are ordered from here. I have two Hammond 290CAX on the way, got em free :icon_biggrin: I just watched some videos on the 1968 Marshall SuperLead and oh boy would that be a nice amp to drive the neighbors crazy
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Made all my changes, wired as per Steve. Just need to hit send and my parts are ordered from here. I have two Hammond 290CAX on the way, got em free :icon_biggrin: I just watched some videos on the 1968 Marshall SuperLead and oh boy would that be a nice amp to drive the neighbors crazy
Best sounding amp I ever played was a super lead 100. They are REALLY a tad too much for the house tho.
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:think1: If I only knew how, Id make that into a 20 something watt amp. Unless it exists, Something like the Trainwreck Version A3 From Doug's Schematics PDF's would work for that vintage Van Halen sound. Need a board tho
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:think1: If I only knew how, Id make that into a 20 something watt amp. Unless it exists, Something like the Trainwreck Version A3 From Doug's Schematics PDF's would work. Need a board tho
Just double a Vox AC10 for your power section. Need to have 4 tubes. EL84 is probably the closest in distorted tone to EL34. Nothing really is like a EL34 and believe you me I have tried to get a superlead tone using less watts.
I did play a SE KT88 build once that had the 2203 preamp and it was closer than what I was trying. Well harmonic wise it was. I think a lot of guys are playing AC30's for this reason.
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So the PT that I pulled out of this build and replacing has found a home. After hearing Dougs Plexi clips I looked at the pdf and low and behold the PT I have will work perfectly. My outputs are on this level for this build, If Doug stocks the Mercury's soon I will stop giving my kids lunch money and buy their OT for this :l2: I will
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be kind to your children - they'll usually be the ones that pick your retirement home or nursing home... :icon_biggrin:
--pete
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I installed the 8 to 9 pin adapter plate, it works great but make sure your 9 pin is 3/4 not 7/8. I thought the ones I have waiting were 3/4 but are 7/8". So I needed to order the correct size. Can't open up to 7/8" to close to screw hole.
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I ment to mention these are new on Doug's parts web page, nice and simple washer
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My two free PT's came in today
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Got the PT in with minor hole adjustments on chassis and she slid right in. The voltages are much better off this one, never mind the reading on the meter there, I made a better and safer test rig and wanted to show it. I had 285-0-285 on the taps I will use. 335-0-335 on the other.
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Any progress?
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Yeah Steve I managed to get the PT in and word back up. I forget to order the smaller diameter 9pin sockets for these adapters. I have the big 7/8" ones, I wound up copying those plates and making a 7/8" one but I don't want to drill out chassis. I'll post my progress pic
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I finished these up tho. P90 fretless CBG and a banjo style CBG for a friend
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Finally got around to putting 9 pin sockets in and start wiring this thing back up. I've been swamped at work and working on my other project.
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Finished the wiring, some triple checking tomorrow and I'll fire her up
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Amp up and running with only minor trouble shooting. Here are my readings and please let me know if it's running to hot, I checked against Doug's and they're close. I did change the 470k going to pin 1 down to 220k. I was going to change some values to wreck values on a similar amp but I wanted to get this up and running. Now I'll slap it back in cab
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Plate dissipation calculation:
The 0.0914A is both plate and screen current. On EL84 I would expect it to be 10% screen, so 0.082A plate current.
The plate-Cathode voltage is 333V-12V or 321V
321V*0.082A is 26 Watts. 13W per tube.
Technically over-spec but probably fine for your purposes.
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So amp is ok but pretty much dimmed out. To drop that down should I go with a bigger cathode resistor like the 250ohm?