Princeton Reverb Build Pt. 1 - Schematic Review 

Great vid. Will really help first time builders.

Nice forensic analysis of the Princeston reverb circuit. Great even if for a novice. Both informative and interesting. A didactic approach with clear understanding.. A must watch if contemplating a build. Cool mod suggestions throughout add a bonus. Tx

Glad I found this. Just got my Mojo Princeton kit.

32:31 I'm only commenting this because its the second video that I've seen you say this. It's a small thing, but... When your guitar signal goes through the voltage divider on the low input, it doesn't see the 1M resistor to ground because the high input jack is grounded when nothing is plugged into it, therefore bypassing the 1M resistor. So, basically the low input is like having a linear volume pot set at halfway.

Really good circuit analysis! Known good mods (I’ve built 2 Princeton Reverb clones/derivatives): 1) adjustable bias with a pi filter (C-R-C) to get cleaner DC for bias and tremolo (I had weird noise issues before adding this on the first one) 2) raise voltage to phase inverter and Preamp 3 (reverb recovery) and add another node on power rail with 240 volts for remainder of preamp 3) slow down tremolo by replacing one 0.1 cap with a 0.22 (forget which one at the moment) 4) replace the 6.8k mid resistor with a 10k or 25k pot. This really makes a nice difference in your control over the tone. The larger pot will start to increase gain and reduce the effectiveness of the Treble and Bass controls. 5) replace the 1 Meg resistor right before the grid of the 12AT7 with a Dwell pot. This gives you control over the strength of the signal going into the reverb tank, while the Reverb control only affects the output from the reverb tank. I also built a Super Reverb with bias vary tremolo and it worked out great.

I really enjoy each of your analysis. Thanks to you, I built my first tube amp. There is hum in oscillator (tremolo) loop. (hum = free electrons with a temperature higher than 0 kelvin.) The hum is amplificated in triode, and next it is 180 degrees shifted in phase by three CR stages. After loop, the signal (hum) has the same phase as before on the grid. That is phase condition. When amplification in triode is equal or higher than attenuation in the loop, the amplitude rises every time (up to a certain value). That is amplitude condition. When both of the conditions are fulfilled, the oscillations are generated. The frequency of the oscillation depends on the R and C value. The speed variable resistor changes that frequency (about 0.5 - 5Hz). That signal flows to the intensity pot (voltage divider) which sets the amplitude of signal. Then signal flows to 6V6's bias, which alters gain of these tubes with frequency of the oscilations (tremolo effect). That's how I understand it.

This is the best deep dive Ive seen yet after the guitologist and Dlabs electronics! Tysm!!🔥🔥🔥

Ok…. We might be dorks…. But this video was….DEEEEE..LICIOUS … You didn't even mention “which way do DC electrons flow”… it kind of doesn’t matter .. But the most fun part was Not even a big deal to you…. Just drawing the signal path from the input jack out through the split at the inverter and then out to the output trans….. I recvd two years of electronics training in High School vo-tech….. so long ago…. We used slide rules… And I was SEARCHING FOR THIS VIDEO…. I had most of the concepts but they were covered 50 years of silt. So …I WILL smash the subscribe…just as my sincere thank you. I have a Twin Reverb… because I can’t afford a Princeton… 1976 with the master volume… If “ everybody hates the MASTER VOLUME”…on those Fender amps….Does just turning the MV to ten “ fix the tone suck”?… or how do you mod to bypass that portion of the circuit? Also in the mid 90s ( functionally PRE internet) in an antique store… I bought a 1950s Gretsch amp… it does power on and play… but 1) the trem only responds with one pulse..and then goes steady… I’m guessing that a cap is charging up… but then…??? 2) because of its age… I am afraid that a cap is going to fail and short…and then smoke the amp… so… A) is this a reasonable concern B) is recapping the whole power supply wise or unwise C) I hate the idea of modding an all original amp… but smoking the amp would be worse. Thank you for the inputs…

Great walk-through on the circuit. I have a couple of amps out of Hammond organs that have 2x6V6s that I'd love to turn into this amp or the 6G2. Maybe both! Your posts on TDPRI have been very helpful as I decide what to go for.

Tube amps are the stuff especially a Fender. Their reverb is second to none in my opinion 😃

You explained everything very well where it was easy for me to understand. Thank you!

Good analysis. One error though, the cathodyne is actually balanced both in gain and output z from plate and cathode, this is because of cathode degeneration feedback provided by the cathode resistor. (The Z balance actually comes from loading symmetrically both sides of the tube)

Hi, i like your analysis of the schematic, very cool ideas!!!

Hello Kley! I can’t thank you enough for this analysis! Best Wishes, Matan🍺

Would love to see a comparison of this and the Princeton Reverb II from the 80's

Id like to see comparation of the classic amps (Fender, Marshall), to lesser known classics like Matamp/Orange, Hiwatt, Magnatone or old Gibson amps.

This is really amazing, thank you so much

It's not really a preference thing, you need to wire the fuse and on/off switch both on the "hot" black incoming ac lead, with the fuse *first*... in other words the first thing the incoming AC hits is the fuse. If the on/off switch were to short to ground somehow, the fuse will blow, but not if it's second in line.

I may be wrong, but the cap/resistor sequence in tremolo section... 3 caps to get to 180 degrees out of phase=60 degrees (not 90) each. Sound right? :) Beautiful build.

Thank you for going through the circuit in such detail. I’ve learned so much watching your videos! Can you reduce the hi input resistor (or replace with a pot to experiment) to get more signal/gain right off the bat, or would that end up being too much voltage for the grid?

I prefer the 5AR4 rectifier to the 5U4 🙂

I’m new to the channel but I have a few thoughts/questions 1 how similar is the Princeton reverb to a blackface bassman? 2 in the PR, is it safe to pull the at7 reverb tube and turn the amp on? 3 I can’t remember what exactly but I got told my Princeton reverb had its “coupling caps” modded so it clips more symmetrically (I could be wrong here) 4 also can you take the reverb send directly into the return without the tank as a kind of boost stage

I am looking at changing the 12AX7 in V1 to a 5879 changing the wiring etc to get a more thicker richer warmer tone. Any thoughts on that? Many thanks for this fabulous overview of the Princeton.

"fantastique" job!! you make the video i was looking for many years, to understand how schematic works. thank you. i'm gonna make a super reverb from mojotone, and i'm looking for informations to understand how these amps works. Could you make the same for the super reverb? and again thank you

Is tremolo a wet effect?

@kleydejong You wouldnt happen to have a CIR or .cir for the Princeton do you??/

The Death Cap "can" send 120v to your strings only if it fails right?

How much you spend on all parts excluding the chassis?

Death caps were primitive line filters. Caps are a short to high frequency current, and since 50/60Hz is pretty close to DC, this won't affect it. Death caps should be exchanged for proper X type line filter caps of apropriate voltage ratings (usually metal film with proper markings including VDE & UL). Eg. many modern SMPS contain a complete line filter including X and Y caps and so common mode ferrite choke, exactly on the input / primary side (110~250Vac), which are able to isolate the device from our noisy power lines. (edited a lot)

The vibrato is a switch to ground or not to ground, vibrato is always on but only has a path to ground when you close the switch. GOD BLESS YOU AND YOUR FAMILY! GOD BLESS AMERICA!! GLORY BE TO GOD!!! IN JESUS NAME I PRAY!!!!!!!