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5881 Tweed Princeton #2

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Mar 26, 2021.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I started a transformer thread about most of this recently, but since it's all nearly come together I thought I would dedicate one for it. I built another one of these for a friend who's actually gigging these days down on Alabama gulf coast area, and he wanted a 12W-15W barn burner amp. I made a few changes from last time: 2.2k bias resistors on both halves of V1, 220k plate resistors, added a 470k screen resistor on the power tube. He wanted it hot and ready, so I left the second gain stage bypass cap hardwired, where last time I switched it as a boost. This time I used a 2.7k and 5.6k NFB option on the switch. ClassicTone is gone, so I used a Hammond 125ESE OT....I'll go with a 125DSE next time! This thing is massive! Bolt spacing is wider than the chassis so I had to mount it at an angle. It's probably the size of a 30W-35W push-pull amp OT. Hammond 290AX PT, and a 5u4 rectifier again.

    A left it turned on maybe half an hour today, chassis turned open end up on the workbench, just letting things get hot. I had a little crackle in the heater wiring develop after yesterday, so I touched it up and left things to get get toasty. Interesting observation: I checked things with my infrared thermometer. I used a 10W 300R bias resistor, so it's pretty big. The ground side of it was 20+ degrees hotter than the cathode end. I checked it a few times, moved it slowly across the entire span. The open chassis was face up, so heat could easily rise, and the + side was closer to the tubes, but the ground side was significantly hotter.

    I'm hoping to get some real mic'd clips done this weekend, but it's a beast with a 1258 speaker, especially with humbuckers! Not exactly an amp to be picking the Wildwood Flower, but if you like Black Keys and blues/rock, it's brings some heat! Now, to finish the cabinet.

    The only clip I have so far, but I've changed it a little on the NFB since then. This is with a Telecaster and the amp on 6, but it has linear pots, so that's relative. I think that was a 12ax7 in V1. A 12ay7 and input #2 actually keeps some really nice cleans if you try.



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  2. Mongo Park

    Mongo Park Tele-Afflicted

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    Angry like Mamas meat loaf with hot hot sauce. With a few of these under your belt you are really getting things dialled in. And seem to be making them as easy as ham sandwiches. Nice work, enjoy your posts.
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks! I'm kinda wishing I'd gotten another Cannabis Rex on the last order, but I got the 1258 instead. I think the 1258 allows more cleans in the right setup, and it really does hold together on the bottom end when it's overdriving. But, the C-Rex just always makes me smile.

    The only thing left to try is find a 6L6 to pop in there. My amp buddy here local has a crazy work schedule, but if I can get with him I want to try one and see. Bias is too hot for a 6v6, but I'm interested to know what the 6L6 sounds like. However, I'm also tempted to do one the same way, except a 6v6 and a 5u4 or gz34 rectifier. Lower output, but the tighter sound beyond the 5y3 rectifier, and the extra gain. I wonder how close it would be. As is, this one really needs a vintage level speaker for that whole cranked at home experience, or a room that handles it well.

    Another thought has been comparing the dropping resistors of the Tweed to the Blackface Champ and wondering what a hotter voltage level downstream would do. It's not going to be this one, but I may experiment. I'm also going to post voltages soon, even if it's for my own reference. I lost my info from the last one, and TDPRI is like cloud storage for these builds!
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, I spent about 20 minutes with my Les Paul plugged in recording it this morning, and looks like it needs some definite tweaking. This guitar has hot pickups - Classic '57 & Super '57 I think, it's a 2014 Traditional Pro II - and it just was way too much crap in the cranked tone. Splatty, farty, boxy, whatever... actually listening back at a reasonable volume is very telling. His guitar is a stacked humbucker & P90, so I know it's not as hot as this one, but this one needs an overhaul still. I think the first step will be to lift the bypass cap on the second stage. I put it on a switch last time, and the guy said he never uses it with the cap engaged, so I'm thinking there is a reason for that... ;-)
     
  5. jsnwhite619

    jsnwhite619 Friend of Leo's

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    And here I am totally forgetting about the difference with the bias & plate resistors this time... :rolleyes: I think I put too much hot sauce into this one!
     
  6. Mongo Park

    Mongo Park Tele-Afflicted

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    Yah you need a hint of clean in there so you can sit on the edge of it and go up from there, or stay there and bring it up with pick attack or pickup switch change.
    I find the bypass cap switch something to engage to give a little bottom end boost at the low volumes. Course I am a tele singel coil guitar person so I dial it for singe coil. Also your plate cathode resistor and higher voltage is giving you more punch and less of the Leo sound, some say Leo went for a sound to try and cut through the mix, which is a good thing and it had less bass in it to do this but could be interpreted as less body as well. He kinda invented that sound......
    If you are going up to 6L6 you might want to go to the 12ay7 tube, I think that is what you used in your first build. Settle on a power tube since you will end up tweaking the preamp again if you change power tubes.
    Yes love the Canibus Rex an fave of mine. Always good to have one in the house at all times.
     
  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    After time to think it over today, I realize I went overboard with everything in the gain department, and did it going against standard practice. Silvertone 1481 & 1482: .01uf coupling caps, 2.2k bias with NO bypass caps on the preamp. GA-5: 220k plate & 2.2k bias but only a single bypass cap and .02uf coupling caps.

    I have .047uf coupling cap, 25uf & 2uf bypass caps, 220k plate resistors, and 2.2k bias resistors. And I'm using a humbucker guitar. It's just too much of everything. Next time I have a chance to mess with it, I'm starting with lifting the 2uf bypass cap on the second stage and go from there.
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, for an update over the weekend, I've pretty much undone everything I changed from the last one. The 220k plate resistors are back to 100k; I left the first 2.2k bias resistor with a 2uf cap (same as before), but went back to a unbypassed 1.5k on second one. Everything with humbuckers was too harsh, too ratty, too much everything, and that's what he'll mainly be playing with it. It's still a screaming little amp for sure, but going back closer to stock Fender levels still sounds way better than the above changes.
     
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  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Btw, I did take the time to change one thing at a time in reverting back. First the second stage bypass, then swapped the first stage 25uf for the 2uf, then the first stage 220k plate to 100k, then the second 220k plate, then finally the second 2.2k bias back to 1.5k. Each step added in the brightness & clarity, and walked away from the nearly square wave sound I was getting with humbuckers. To my ears, when I finally replaced the second bias resistor and played it again, it was almost like a different amp. The volume & clarity both seemed to increase.

    In more reading and conversations, I'm pretty sure that my original setup would have been more likely to work if I'd allowed for a voltage divider in the preamp to dump signal along the way. This one will remain as is, but I think I will be adding the eyelets to my layouts in the future for any experimental stuff to include the option even if it isn't used. Also, I think the original plan would probably be closer to working in a Treb/Bass tone stack rather than the single knob on this one, aided by extra signal loss and the ability to tweak the EQ a bit.

    Any thoughts or opinions on "what went wrong" are welcomed.
     
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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    In continuing with this thing, I tried it through my pine Pro Jr cabinet with a 1058 in it - sounded much smoother to me and less ratty & harsh. Last time I got a Cannabis Rex, but I had just gotten this 1258 for something else and planned to just use it this time.

    So, two possibilities right now - the 1258 isn't broken in very well yet so it needs to mellow out, or it's just the wrong speaker for it. So, the 1258 is hooked up under a moving blanket, piece of plywood, and a trash bag of sawdust right now with a solid state stereo amp cranking out the full Grand Funk Railroad discography, and we'll see if I can do anything to that speaker while I finish the cabinet.

    I got some decent clips - I think - of the 1258 today, but I have sorted through it yet. Will post it up when I do, maybe later tonight.
     
  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Any suggestions or feedback on cleaning/tightening this up are appreciated. Pearly Gates & 12ay7. I work back & forth on the NFB switch. The rhythm parts in the beginning aren't bad at all for a good rock tone, but the lead runs & single note stuff just falls apart. Like a fuzz. The last 30-40 seconds of it show what I'm talking about. I did some with a 12ax7, but you can imagine what it was doing -- like this x2.

     
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  12. Mongo Park

    Mongo Park Tele-Afflicted

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    You need more clean, this design originally produced most of its dirt from the power tube. In this case I think it is coming from the preamp tubes.
    What is your plate voltages and cathode voltage of the preamp tubes.
     
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  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I haven't checked it since I swapped all the plate & bias resistors. Might be a good idea. ;-)

    To keep everyone else up to speed, I thought about what I've preached with my 6v6 builds like this in the past and I decided I liked keeping the 8-10uf filter cap on the preamp node. I used a 22uf here b/c "bigger = better" and I was using bigger tubes. I swapped the 22uf for a 10uf tonight, but I'll have to wait til tomorrow to crank it and try it. My reasoning in the past was that it seemed to keep the mud out and maintain clarity compared to higher values there....go figure.
     
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  14. Mongo Park

    Mongo Park Tele-Afflicted

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    You might want to try a small bypass cap on V1a something like .68 if
    Even the minimum 5F1 people put a cap on or things are to anemic
     
  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I feel like I need to bring @cobaltu and @tubegeek into this conversation, continuing where we left off last year. I was measuring my voltages on this one and the plate voltage was very low with the 12ay7 and 100k plate. Then I remembered all the discussion in the last thread about optimizing the 12ay7 - something nobody really does. With only 114v on the plates, I figured that some of my bad fuzz had to be coming from that. I found a thread elsewhere and the guy compared voltages simply by swapping tubes found that while a 12ax7 had 200v, the 12ay7 had 146v....a pretty big drop. So, back to last year's thread I went. https://www.tdpri.com/threads/5881-in-a-5f2a.1036053/page-3

    I swapped both 100k plate resistors to 82k and fired it up. Plate voltage went from 114v to around 145v. Way more punch & clarity. The trashy fuzz overtone went away.

    I also removed the 2uf from the input and replaced it on the second stage. I tried it with no bypass just to see, and there's still plenty of drive, nice & soft and vintage sounding. But, in thinking that I was overloading my preamp, I placed the bypass farther down stream. Then, when I was checking voltages again, it hit me that my plate voltage was so low. I have 1.5k bias resistors on both halves at this point, don't know if I'm going to play with that anymore.

    Here's a quick one, 0-45 sec. on 5, next bit on 10.

     
    Last edited: Mar 31, 2021
  16. cobaltu

    cobaltu Tele-Meister

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    I saw my 'Bat Signal'!

    Okay so where is the amp at now? Put another way: how does it currently differ from a regular 5f2-a?

    That new 12ay7 bias definitely sounds a bit better. I would try taking the first stage's cathode resistor to ~2.2K. The first stage doesn't really produce any/much distortion anyway, so that might be a good way to keep the second gain stage from going too 'ape', too fast.

    Is the negative feedback still ~5.6K? I've experimented the hell out of negative feedback resistors in my Allen "Classic 10" and AAaallways came back to the stock 22K. Granted my amp still has a 12ax7 in the V1. I found that going lower on the negative feedback always made it too raspy/edge. Very a similar sound to what you're getting in those recordings.
     
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  17. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Welcome aboard! Current preamp specs:
    • 1.5k bias resistors
    • 82k plate resistors
    • first stage is not bypassed
    • second stage has 2uf bypass; used a Blackface style NFB with a 47R tail resistor, 5.6k & smaller NFB value. Allows for NFB and a bypassed gain stage. There is a switch, but I'm still playing with values here.
    • stock .022uf coupling caps
    • separate inputs, both with 1M input resistors; #1 is 34k, #2 is 68k. Significant difference in clean & dirty between them.
    Power section specs:
    • 5u4 & 5881
    • 30-22-10 filter caps. The 10uf definitely helped cut bass & mud.
    • stock dropping resistors - 10k & 22k
    • 1.5k and 470 resistors on the power tube. 390v B+

    I'm not really happy with my demo recording because the difference seems to be much greater in the room & live. Getting that 12ay7 plate voltage up made a huge difference. It's a lot cleaner at lower levels, and overdrives better. I'll have to wait til tomorrow to get all the voltages in the preamp now. I didn't note anything except the plate.

    I started things with 2.2k bias resistors, but changed those before I put 2+2 together with my plate voltage being so low.
    • I hated the 220k & 2.2k combo.
    • 100k & 2.2k was better.
    • 100k & 1.5k was better than that.
    • 82k & 1.5k is best so far.
    It's been a process....but my buddy is loving the sound clips and isn't in a hurry, so I'm getting time to experiment.
     
  18. kleydejong

    kleydejong Tele-Holic

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    Love the experimentation and the clips!

    One conclusion I drew in m 5F2A and 5E3 journey was that a lot of what I heard as 'splatty' or 'fuzzy in a not so great' way tone has a lot to do with midrange - not just low end. So I really like adding a Framus mid control or even a full on AB763 style tone stack with a bypass switch on the mid ground connection.





    I also like a little higher plate voltage. I found that messing with the 22k step down resistor going to 10k or even 4.7k helps a lot. I even experimented with putting a 22k and 4.7k on a switch once!

    Adding some NFB and a tone stack will COMPLETELY add a new midrange character to the amp. One that I really prefer. Add the bypass caps on the cathode back in so you don't lose too much gain.
     
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  19. cobaltu

    cobaltu Tele-Meister

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    I think I might know where some of your wonkiness is coming from, but it's a bit hard to explain.
    The cathode bypass cap on the second gain stage is not large enough allow all the negative feedback signal into the cathode. Because it is so small, it is actually refusing low frequency feedback into the cathode. This would likely express itself as a boosted, looser bass response. Sort of like the opposite of a presence knob.

    I once did a similar thing on a LTPPI decoupling cap. I made the usual 100nF cap that bypasses signal off the non-inverting side to a 22nF cap. The idea was to improve the recovery of that side of the PI to make it punchier. Normally, this would work, but if neg-feedback is being injected into the PI, it only pulls off most of the bass, but not all. It made this weird kinda bass response that sounded like the bass was kinda out of phase and coming from a different speaker. I put it back to 100nF and the bass focus came back.

    Recommendations:

    1) Move the cathode bypass cap to the first gain stage, and leave the second stage unbypassed.

    2) Change the second stage bypass cap to ~22uF (allow all audible neg-feedback into the cathode), and rely on coupling caps the trim bass. I would change the first coupling cap to ~2.2nF/0.0022uF to mimic the same bass roll-off. This would mimic the negative feedback of the Princeton more. *Preferred*

    That being said if you like it leave it as is.
     
  20. lathoto

    lathoto Tele-Meister

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    Franklyn Amps put a mod in my customized Tweed Princeton which allows me to swap out the rectifier and the power tube. When I use the 6L6 it sounds dark and glassy. The clean highs come from the EVM12L (recommended). What puts it over the top is the EVM15L extension speaker to push the bass.
     
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