Princeton Reverb Build Pt. 1 - Schematic Review

In this video I start a Princeton Reverb amplifier build by doing a deep dive analysis and review of the schematic explaining how each component in the circuit works.
Hit "Subscribe" for more videos!
kzbin.info_c...
Grab some cool merch and support my videos:
Tip Jar - paypal.me/kleydejong
kley-de-jongs-tone-store.crea...
If you wish to support my videos please visit my patreon page at / kleydejong .
Links:
My Soldering Iron - amzn.to/2PAVwUb
My Audio Interface - amzn.to/3kcJKuo
My Studio Studio Monitors - amzn.to/3dtSFpH
My Picks - amzn.to/2NobVdB
My Favorite Pedal - amzn.to/3k5OJN9
My Favorite Mic - amzn.to/2NfhDPe
My Camera - amzn.to/3qCD8I2
My Favorite Strat Pickups - amzn.to/3dsLC0H

[@darrylgross8768]

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

[@jonjames1998]

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

[@czgunner]

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

[@maxrado5172]

Same here. Can't wait to build it.

[@TheJurgisRud]

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.

[@mikepaul77]

On my 68 Custom Vibro Champ Reverb, I’ve found if I use the low input jack for my guitar signal and plug a 1/4” to 1/8” adapter in the high input jack, it lifts the direct ground connection and makes a much fuller and interesting tone with only slightly less gain than input 1. I guess the low side signal is only going through the one 68k resister vs 34k total on the high side at that point, with very little signal sent to ground through the 68k and 1 meg resister. Does that sound right? Essentially making it just like he says in the video. I only found this trick accidentally one day when a cable was plugged in both jacks at the same time.

[@joeltunnah]

​@mikepaul77 you're correct. Plugging a dummy plug into input 1 will give you the 1M grid resistor back, so you lose much less signal. If you only plug into input 2, it's only 136k off the grid to ground, so you're loading the guitar down more... and you're taking the signal from between the two 68k resistors, so you're also throwing away 6db of signal. I really hate Fender's input wiring.

[@damianturzynski5941]

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.

[@chipsterb4946]

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.

[@sempercompellis]

I love bias wiggle trem and would love to get my 6l6 blackfaces to do that- did you write down any notes or schematic to add bias vary to the ab763 circuit?

[@analogblues9606]

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

[@Matan2222222]

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

[@JuanMotta]

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

[@MarderExplorer]

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.

[@joepirrie5548]

This is really amazing, thank you so much

[@wadehicks9270]

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

[@PurposefulPorpoise]

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

[@MrKeithhanson]

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?

[@leandrocarg]

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)

[@stanislavmigra]

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

[@joeltunnah]

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.

[@waldodontliveherenomo2488]

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.

[@Tuxtitoo]

"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

[@KC9KEP]

I prefer the 5AR4 rectifier to the 5U4 🙂

[@Billywagner22]

Me too

[@annarakannan6620]

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.

[@KleyDeJong]

A 12AX7 is a dual triode and the 5879 is a single pentode. So you'd have to drill an install an additional 9 pin tube socket and then not use one of the triodes in the 12AX7. But other than that it would be fine. I have used pentode as input tubes in my 6AU6 Princeton build. It works and sounds great. kzbin.info/www/bejne/ql7SZYaNaNhorbs

[@OneMomentFromForever]

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

[@KleyDeJong]

1 - Not very similar at all. 2 - Yes. You can pretty much always turn an amp with with a tube missing, it simply won't work - but it won't damage things. 3 - It does have coupling caps. Coupling caps exist to 'decouple' or prevent the high voltage DC that powers the tubes at the plates from the next stage in the circuit. You can also change the low end response by using different values. A large value like .1uf will make the amp bassier. A smaller value like .0022uf will trim bass making it tighter and brighter. Coupling caps would not affect clipping symmetry. That is more something you would achieve with how you use diodes in an overdrive pedal. Perhaps you can affect the clipping symmetry by changing the values of the resistors on the plate and cathode of a 12AX7. A cold clipper using a 10k cathode bias resistor would clip very asymmetrically. 4 - Yes you can do that. It would make the reverb knob a new volume knob to control how much boost you add.

[@joepirrie5548]

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

[@larryjeffryes6168]

Is tremolo a wet effect?

[@iplayloud2]

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

[@KleyDeJong]

Correct. If it fails open.

[@gerardoromano3436]

Hi, It can send 120v to your strings if it fails "short" rather than open

[@kirstencristobal3204]

How much you spend on all parts excluding the chassis?

[@KleyDeJong]

I don't have an exact count. I grab random components all the time for builds. I've built amps as cheap as about $200 and up to about $600 for a kit I built early on.

[@kirstencristobal3204]

@@KleyDeJong for 200 dollars what amp clones can i build?

[@KleyDeJong]

@@kirstencristobal3204 Start with a 5F1 champ as a head.

[@kirstencristobal3204]

@@KleyDeJong is that the 5watt 1957 Champ?

[@KleyDeJong]

@@kirstencristobal3204 Very similar. It adds a tone control, some extra filtering, and had a larger combo cab with a 10" speaker.

[@jamesbracken4618]

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!!!!!!!

[@bobyk87]

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)

[@joeltunnah]

It's completely against code. There is no way for it to be "well done", and it's unnecessary. The noise coming from your pickups is going to swamp anything on the AC line.

[@bobyk87]

@@joeltunnah the "death cap" was the precursor to modern "line filter" caps, in this case the "X type Capacitor" is what I mean, which is designed to fail open (instead of shorting and burning things). Check out the X and Y caps in the stadards IEC 60384-14, UL1414 and UL1283. But I agree with you keeping old generic type caps there is against code. So in my opinion the technician has two options: replace improper ones to proper X type or just remove them. But technically speaking they were put there to filter line noise. BRegards.