Can Someone Proof My Schematic? BF PR

[Milnoque]

I drew this schematic for my BF Princeton Reverb project. I wanted to be able to document later mods and such. I thought it would be useful to number the resistors and caps so I could ask questions later. I am hoping someone out there can review it and tell me if I missed anything or got something wrong.

I drew it in autocad so I can fix any errors you might find. When finished I'll be glad to share it with anyone who could use it.

[sportster4eva]

At a quick glance Your +420v B+ has to go to the middle of the left side (primary) winding of TR2.

[Milnoque]

Like this?

[sportster4eva]

Yep, that's the ticket

[Milnoque]

Thank you very much for the time you took. After I work on one of these it gets to a point where I can't see it right any more.

I learned alot from going through the exercize of working this drawing up.

If anyone looking at this thread can use this drawing, feel free. I can also provide the Autocad version.

Thanks for the help

[sportster4eva]

You did a nice job on that! Must have taken a while...

[Bruce / Mission Amps]

I would not use a 5Y3 rectifier in this application.
I don't know where you are going to get the power transformer from but make sure it is the right one for what you are trying to do here.
If you use a PT with a 3a 5v secondary, you can use a NOS 5U4GB.
If it does not have a 5v@3a secondary you might want to look into a NOS 5V4GA.
If the high voltage secondary is low enough, a reissue 5AR4/GZ34 would be the way to go.

[Milnoque]

Thanks Bruce,

Actually I bought the PT from Allen Amps and he made the same recommendation. I'm using a GZ34 I just forgot to make the correction on the drawing. Thanks for the heads-up. I'll fix this ASAP.

I'm really glad you guys are here. I'm hoping you will keep holding my hand as I go forward.

[Milnoque]

Updated Drawing

[sportster4eva]

Bruce, I'm curious, would the 5y3 be unsuitable because of the current draw?
Fender did use a 5u4 in that amp, but it's similar to a lot of other Fender circuits that use a 5y3. I'm puzzled by that.
Thanks,
Paul

[Bruce / Mission Amps]

Bruce, I'm curious, would the 5y3 be unsuitable because of the current draw?
Fender did use a 5u4 in that amp, but it's similar to a lot of other Fender circuits that use a 5y3. I'm puzzled by that.
Thanks,
Paul

Contrary to what many people think, the PR can actually push about 16-18 watts of fairly clean power through it's little OT.
It simply is a different amp with a different design goal.
The BF fixed bias Princeton can push more clean output power then the tweed (and most brown) 6V6 amps.
The amp actually used a higher voltage yet smallish, Champ sized power tranny, around 70-90 ma, and made up for the simple "power = V*A" equation through the OT by using more V then A... etc. That takes a stiffer rectifier with less impedance.
The 5Y3, with it's higher impedance, would bring the V part way down and the same amp might only be able to muster something in the 12 watt clean power range. It would work fine and be fun to play but I suspect not get as close to the classic black face Fender sound.
As far as the 5U4 in this amp, well, even though also a higher impedance tube like the 5Y3, it is VERY lightly loaded in this amp so the B+ will be much higher (vs the little 6V6s)... then what you normally see when used in a 6L6 amp with 6 preamp tubes.
The 5AR4/GZ34, depending on the PT, will up the B+ too.
With the power tubes running in fixed bias at around 8 or 9 watts and that higher B+, the little PR is a screamer when driven hard.

[Milnoque]

Does that mean that if I'm willing to give up the output power I can mod it for a 5y3 at a later date without harming the amp? I'd be interested in hearing the difference.

I also want to try it with cathode bias. Perhaps try a 12AU7 in the first stage.

First things first though, I'm going to build it as designed. I may love it that way, but I'm still going to bugger it up later.

I chose this amp so I could use it as a platform for experimentation. I use electric guitars mainly in an acoustic guitar setting. I don't really care about output volume. I want a lower powered amp with reverb and tremolo.

[Paul P]

I suggest you change your AC mains wiring to the PT. This is one
part of the original circuit that you shouldn't copy. Nowadays it is
done like this (in North America) :



Paul P

,

[Milnoque]

Maybe this is a stupid question, but why does it matter whether you switch the hot or the neutral in this type of circuit?

[Milnoque]

Nevermind, I just answered my own question.