Princeton / Champ never seems to break up like "Layla"

drew1d

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I've built a few and always get too much clean headroom. like no breakup all the way to 12. I figured it's because the voltages always seem too high. Like upper 300s on the power tube, and low 300s on the preamp. (Anode voltage) Any tips on getting that Layla sound, or is it recording mic placement?
 

Whatizitman

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Strum/pick harder? Humbuckers/P90s? :confused:

Truthfully, this is the first time I can remember reading someone complaining about tweed champ headroom. I first figured it was for BF/SF, of which voltage could be part of that equation. But tweeds are generally not an issue for breakup.

Use less efficient speaker and/or an attenuator, perhaps? Maybe you can tweak anode or screen resistance? Just spitballing.

To me, any close mic'ed amp signal is gonna sound more compressed and distorted than live in the room. So definitely experiment with placement, too.
 

D'tar

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Mind sharing more info? How about some photos? Complete voltage chart? Is everything stock? 6v6 bias resistor 470 ohms? bypass caps in place? stock NFB circuit?
 

Chiogtr4x

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This is probably no help as I've never really owned either of those amps but I did remember reading that I think Clapton used to turn the Princeton all the way up and the treble all the way up
 

drew1d

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I've tried it with a few different speakers. PMR 8" hemp super heavy thing, 8" Alnico Jensen, 12" PMR Rockness monster, 10" Tone Tubby Humboldt. I had a MOJO tone nos 5w OT. But i'm moving to a 8W SE one. 500 Ohm Cathode resistor for 6v6. I have a 330-0-330 70ma. It had a SS rectifier I'm in the process of moving it to a new cabinet and chassis, and wanted to see if there was anything I can do to make it get that Layla sound.
 

jsnwhite619

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I've tried it with a few different speakers. PMR 8" hemp super heavy thing, 8" Alnico Jensen, 12" PMR Rockness monster, 10" Tone Tubby Humboldt. I had a MOJO tone nos 5w OT. But i'm moving to a 8W SE one. 500 Ohm Cathode resistor for 6v6. I have a 330-0-330 70ma. It had a SS rectifier I'm in the process of moving it to a new cabinet and chassis, and wanted to see if there was anything I can do to make it get that Layla sound.

The SS rectifier is a big part of the problem, if not all of it. Stick a 5y3 in there, be sure you have a bypass cap on V1, and a 12ax7 in the slot. If that doesn't do it, I'd suggest a circuit issue.
 
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ArcticWhite

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The SS rectifier is a big part of the problem, if not all of it. Stick a 5y3 in there, be sure you have a bypass cap on V1, and a 12ax7 in the slot. If that doesn't do it, I'd suggest a circuit issue.
Someone will be along shortly to contend that a tube rectifier won't matter in a Champ, (because single ended amps don't sag?).
I don't know enough to offer an argument, but I'm here for it .
 

Whatizitman

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Someone will be along shortly to contend that a tube rectifier won't matter in a Champ, (because single ended amps don't sag?).
I don't know enough to offer an argument, but I'm here for it .

Sag may not change. But voltage can. SS will run higher voltage, which would have to be compensated down stream in the circuit. I don't know enough to say. But I think 330-0-330v is pretty standard for a tube rectified champ or princeton. That would yield pretty high plate voltages with SS rec in an unmodded circuit.

OP, what's the bias/dissipation at 500ohms? If the 6V6 is well over 100% dissipation, it's gonna break up a lot less.
 

drew1d

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Well, I think the 5y3 would lower the voltage quite a bit compared to the SS. That's what I think the point he was trying to make. Part of the reason I did was that the Transformer had a broken 5v tap. (only one side worked.) Then I figured, I'd try the Heyboer Transformer from Weber....but I fear it's going to be too high of a voltage. I bought the one for the champ, but it wasn't specific on it's specs....I should have been more critical. I started poking around and think it might even be higher.....uggh...
 

drew1d

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Sag may not change. But voltage can. SS will run higher voltage, which would have to be compensated down stream in the circuit. I don't know enough to say. But I think 330-0-330v is pretty standard for a tube rectified champ or princeton. That would yield pretty high plate voltages with SS rec in an unmodded circuit.

OP, what's the bias/dissipation at 500ohms? If the 6V6 is well over 100% dissipation, it's gonna break up a lot less.

I'm not sure. I have it apart at the moment. When I get the new transformer, I'll measure it. Just got to dig up that Ohms law....what was it again....beer before liquor....wait a sec, I think I'm mixing it up with something else. I got Jack Dar's book around here somewhere...
 

jsnwhite619

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Someone will be along shortly to contend that a tube rectifier won't matter in a Champ, (because single ended amps don't sag?).
I don't know enough to offer an argument, but I'm here for it .

I'm not going to get into it about it for argument's sake on the "sag" issue, but there's night & day difference in the tone and response between a 5y3 and GZ34 in the one's I've built. Way more headroom and punch with the GZ34. I've posted it several times, but the guy who ended up with this 5f2a has a GZ34 and C10Q and uses it as a clean pedal platform with his Les Paul because it has the headroom to do it. Leaves his '68 Custom Vibrolux at home most of the time now. I don't have a GZ34 demo with it, but this is a Nashville Tele and 5y3 for an example of something that is the exact opposite of what I just described. I know the voltage is higher, but if you swap the 275v secondary for the 325v option and use a 5y3, the voltage is dang near what the 275v gets with the GZ34, and 375v B+ both ways just does not sound the same. The 5y3 is recognizable in tone and headroom at 340v or 380v in comparison.




Well, I think the 5y3 would lower the voltage quite a bit compared to the SS. That's what I think the point he was trying to make. Part of the reason I did was that the Transformer had a broken 5v tap. (only one side worked.) Then I figured, I'd try the Heyboer Transformer from Weber....but I fear it's going to be too high of a voltage. I bought the one for the champ, but it wasn't specific on it's specs....I should have been more critical. I started poking around and think it might even be higher.....uggh...

Hammond 290AX with the 275v secondary will hit dead on 340v B+ with a JJ 5y3, per the vintage 5y3 layout diagram.
 

Bryan A

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Hmm. Clean headroom is something my 57 Champ does NOT have. It starts breaking up around 3.5-4 and goes from pretty gnarly to flat out nasty between 7 and 12.
 

drew1d

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The one on the right. I had that PMR heavy magnet 8" and an Alnico Jensen 8" wired in parallel for the 4ohm (8+8) OT. I wanted to move to a single speaker, so I got a 8ohm 8watt SE OT. I also bought a cabinet and chassis for a fender champ. (I will sacrifice one of the inputs for a tone, I only plug into one anyway.) As clean as the day is long though.... I'm using this chassis now to do an experiment with. (Cascode, SE) So realistically, I'm just using the circuit board from this amp. As I get the last parts for the champ, I'll take another picture.
 




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