Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colinblakely on September 15, 2026, 04:46:48 pm

Title: Questions/Feedback- Modified Princeton Reverb Build
Post by: Colinblakely on September 15, 2026, 04:46:48 pm

Hi All,
I would be grateful for advice from those more knowledgeable than I!

Several years ago I built a modified Deluxe Reverb. I added a Type 2 PPIMV, PPI Treble cut and Robinette's lead channel mod. I really love the sound and range of the amp- from classic DR cleans to really nice preamp overdrive at reasonable volume levels. Now, I'm interested in creating a Princeton Reverb with a similar range. However, with only one channel, I'm trying to incorporate the lead channel mod via switching.

I'm attaching the schematic and layout I've worked on. I ended up removing the tremolo so that I didn't have to cram in the other mods. A few questions:

• Keeping the reverb but deleting the tremolo, how do I go about calculating the value of the voltage dropping resistors? I'm still working on understanding the math behind all this. Also, are there other missing modifications I need to make to account for in deleting the trem?
• I have limited experience with switching and want to make sure I've set things up correctly in my schematic and layout.
• Any general feedback on the concept and design of the circuit would be appreciated.

Thanks!!
Colin

Title: Re: Questions/Feedback- Modified Princeton Reverb Build
Post by: dogburn on September 15, 2026, 05:03:18 pm

I can't comment on most of your switch mods, but I think the raw switch looks good. But what's that 1M resistor on the switch for the V1a cathodes?

Since you deleted the tremolo, you might want to do a one-tube reverb here and that way you can eliminate one whole tube.

Title: Re: Questions/Feedback- Modified Princeton Reverb Build
Post by: passaloutre on September 15, 2026, 06:06:48 pm

I don’t care much for the Vox cut control, but some people do, so go for it.

I think your preamp gain switch will be a nice second voice.

On “Raw” switching, I’ve had better luck, rather than completely eliminating the ground reference for the tone stack, adding a big resistor in series with the 6k8. 100k is enough for me but you could try a 250k or 1M. Variation on this theme is to make it a potentiometer, so you can dial in your rawness.

Title: Re: Questions/Feedback- Modified Princeton Reverb Build
Post by: Colinblakely on September 15, 2026, 10:06:17 pm

Thanks for the quick replies! Dogburn, I am not familiar with a one tube reverb design, but I will do some research. I would love to drop a triode so I'm not leaving one wasted. I never get past 3 on my DR reverb (even with a 12AU7 driving it), so a single tube reverb might work even better.

I found information suggesting the 1M resistor would keep the capacitors on both sides of the switch charged and thus reduce the likelihood of popping when I switch over.

Passaloutre, I have a 250K raw pot installed in my DR in lieu of eliminating the ground reference, but I find I'm only ever using it at 1 or 10. I'll experiment with a fixed resitor instead.