Another Princeton Reverb Build

[theprofessor]

I've got it all buttoned up now. Hammond 290AX PT and Hammond 1750H OT. A 1963 Tung-Sol 7025 in V1, an RCA 12AU7 mil-spec (5814A) short black plates in V2, a Tungsram ECC83 in V3, a JJ ECC83 in V4, a pair of 1950's Sylvania gray glass 6V6GT's in V5-6 (one labeled Philco, one labeled FoMoCo), and a 1962 RCA 5U4GB in V7. I ended up biasing it at around 18 and 20mA plate current for the pair of 6V6GT's at around 399 volts. Sounds great! (and the noise floor is very, very low).

 

[chas.wahl]

Exceptional-looking amp!

 

[SnidelyWhiplash]

The TDPRI faithful demand sound clips!

 

[theprofessor]

The TDPRI faithful demand sound clips!

Shoot! You’re right to call me on it, but it’s already boxed up and ready to travel tomorrow. Sorry!

 

[SnidelyWhiplash]

I was just teasing. I wouldn't inflict my infidel playing on anyone. No right to ask you to do so.

 

[theprofessor]

I was just teasing. I wouldn't inflict my infidel playing on anyone. No right to ask you to do so.

Hahaha! Well I don’t mind you challenging me to do so!

 

[theprofessor]

Here's the final pic of the inside of the working amp. I ended up taking the chassis out one more time to replace a 1M resistor in the tremolo oscillator string headed to V4, pin 1, with a 470k one to increase the tremolo intensity. Worked a treat!

 

[SnidelyWhiplash]

I did the same mod to my PR. Makes the trem a lot more useful.
The chassis looks immaculate, tp!

 

[Greg70]

Beautiful build! I love the grill cloth too. I'm assuming that's a mid pot in the ground switch hole?

 

[theprofessor]

Beautiful build! I love the grill cloth too. I'm assuming that's a mid pot in the ground switch hole?

Thank you! Yes, it’s a mid pot. Works very well.

 

[PhatFinger]

I've built another Princeton Reverb -- this time for my college roommate. I built him a thinline two-P-90 T-style last year, and so this year, it's an amp. I've built several of these Princeton Reverb clones using the Doug Hoffman layout, and I decided to do that again (with a few modifications). Some new things for me on this build: I used ZERO cloth pushback wire, which I love. I also used a lot of stranded-core wire, versus solid core. Finally, I used all metal film resistors, with the exception of the 470k carbon comp I added before the grid of the phase inverter. We'll see how it sounds.

I also decided that I wanted to experiment with a slightly different aesthetic than the common blackface PR type. I got some Dumble/Vox style grill cloth and used that. Hoping it all comes together well. I think it will!

AS previously, I used a Hammond 290AX PT. I found a used Classictone 18002 Deluxe Reverb type OT, and I used that (I have that in my PR clone as well). A Mojotone reverb transformer. Cabinet is from Guitar Cabinets Direct, though I modified it slightly. And a Celestion G10 Vintage speaker, which I think suits this circuit very well.

Now I just have to check everything against the layouts and schematics, and then I plan to go through the startup procedure tomorrow. I'd appreciate it if you see any mistakes!

View attachment 987696
View attachment 987697
View attachment 987698
View attachment 987699

 

[PhatFinger]

May I ask: Where are you sourcing the Chassis, faceplate, components? Referral wanted.

...beautiful work, man.

 

[theprofessor]

May I ask: Where are you sourcing the Chassis, faceplate, components? Referral wanted.

...beautiful work, man.

Thank you very much! I get my chassis from Zach Hunter in Little Rock. He has an ebay store. The faceplate is from Sandy Henry at Precision Design. Most of the components are from Doug Hoffman and from Tube Depot.

 

[jellodog]

The Fender shapes and orientations just make sense to me, and Hoffman's layout, while optimized for ground-points and several other things, feels like thinking backwards and inside-out. To further exacerbate the issue, his layout is incomplete and often looks nearly nothing like what an actual amp chassis built on his layout looks.

I'm curious - what is incomplete in Hoffman's PR layout? Or perhaps there is too much to go into here. Until I read your commnet on this topic, I was tempted to give the Hoffman layout a try.

On the other hand, I've never built a PR before, so at least if things go wrong; I can compare my build to many many online photos of other people's builds (and/or solicit feedback here). Less so, the Hoffman.

Beautiful and inspriing build, BTW.

 

[theprofessor]

I'm curious - what is incomplete in Hoffman's PR layout? Or perhaps there is too much to go into here. Until I read your commnet on this topic, I was tempted to give the Hoffman layout a try.

On the other hand, I've never built a PR before, so at least if things go wrong; I can compare my build to many many online photos of other people's builds (and/or solicit feedback here). Less so, the Hoffman.

Beautiful and inspriing build, BTW.

Thank you! Let me say first that I've built at least four Princeton Reverbs on this Hoffman layout. There's a reason I've done that: they sound great and are _very_ quiet.

There is nothing _wrong_ with the Hoffman layout. But there are some things that annoy. For example, the main things that bother me is that the tube pin orientations are all wrong and that the layout is not even close to scale. While scale is never exact, at least a build according to the traditional layouts will look somewhat like the layout itself. Another thing is that he does not include any of the power wiring. And, for some reason, he includes only one input. If you know what's going on, it's no big deal to change, but I have to keep up with such changes as I go, and it can be challenging to keep up with where you are in the build, since the build itself does not bear much resemblance to the layout.

For a first-time build, I'd highly recommend using @robrob 's Princeton Reverb layout and following it to a "t." I'd go for a lower-voltage power transformer than what he lists, but you can pretty much just copy everything else exactly and it will turn out great. And you're right: that layout is classic, and it's easier to troubleshoot -- probably for everyone.

 

[jellodog]

Thank you! Let me say first that I've built at least four Princeton Reverbs on this Hoffman layout. There's a reason I've done that: they sound great and are _very_ quiet.

There is nothing _wrong_ with the Hoffman layout. But there are some things that annoy. For example, the main things that bother me is that the tube pin orientations are all wrong and that the layout is not even close to scale. While scale is never exact, at least a build according to the traditional layouts will look somewhat like the layout itself. Another thing is that he does not include any of the power wiring. And, for some reason, he includes only one input. If you know what's going on, it's no big deal to change, but I have to keep up with such changes as I go, and it can be challenging to keep up with where you are in the build, since the build itself does not bear much resemblance to the layout.

For a first-time build, I'd highly recommend using @robrob 's Princeton Reverb layout and following it to a "t." I'd go for a lower-voltage power transformer than what he lists, but you can pretty much just copy everything else exactly and it will turn out great. And you're right: that layout is classic, and it's easier to troubleshoot -- probably for everyone.

Thank you very much for your thoughts. I think that you may have prevented me from embarking upon an unwise choice for a first PR build. I am better sticking to the well worn path and being able to compare to other people's build photos.

 

[theprofessor]

Thank you very much for your thoughts. I think that you may have prevented me from embarking upon an unwise choice for a first PR build. I am better sticking to the well worn path and being able to compare to other people's build photos.

I agree. Again, it's not that there is anything wrong with Hoffman's layout. The layout is probably the reason it's quiet. But it's not ideal for a first-time builder, and you can still get a quiet PR build with the traditional layout.

 

[Kevin Wolfe]

Great information @theprofessor. I’ve often heard how quiet the Hoffman design can be but to hear from someone who’s built both versions is quite useful. Thank you sir.
oh, and I love your work, by the way.

 

[theprofessor]

Great information @theprofessor. I’ve often heard how quiet the Hoffman design can be but to hear from someone who’s built both versions is quite useful. Thank you sir.
oh, and I love your work, by the way.

Thank you very much! That is too kind!