Princeton Reverb build

[peckjed]

Hey all, just finished up a Princeton Reverb build! Sounds excellent and for once didn’t require a ton of troubleshooting to get it running.

I added a negative feedback switch at the back (2.2k, 5.6k and stock). Makes a subtle difference.

I also added a 50k linear mid pot with the 6.8k grounded to the pot so when the pot of set to 1 it’s effectively stock. That 50K adds A LOT of gain.

Also added a 470 ohm grid stopper to the PI.

My question - is there anything obvious I didn’t do that would be helpful to quite it down anymore? It’s pretty quiet as is, but if there’s anything stupid I did. I’d happily correct.

Also - any way to smooth the gain a bit?

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[Colossal]

Also added a 470 ohm grid stopper to the PI.
Also - any way to smooth the gain a bit?

Very nice! Princetons are great amps. Usually, the cathodyne PI grid stopper is much larger, on the order of 100k to 470k. You might want to try increasing your 470 ohm to 470k and see if you like what it does to the overdrive.

[ViperDoc]

I put a 470K on the PI on my Princeton and it sounds great. What made an equally impressive difference was testing the amp through a Warehouse Veteran 30 speaker. I started with a Warehouse ET65 and that sounded great, but if you’re looking for forward, all-out American crunch from a Princeton, it might not get much better.

[peckjed]

Also added a 470 ohm grid stopper to the PI.
Also - any way to smooth the gain a bit?

Very nice! Princetons are great amps. Usually, the cathodyne PI grid stopper is much larger, on the order of 100k to 470k. You might want to try increasing your 470 ohm to 470k and see if you like what it does to the overdrive.

Ah 470K. I bought the wrong value. What sonic impact should I expect when changing the value? Should I add grid stops and screen resistors to the 6v6's as well?

[peckjed]

I put a 470K on the PI on my Princeton and it sounds great. What made an equally impressive difference was testing the amp through a Warehouse Veteran 30 speaker. I started with a Warehouse ET65 and that sounded great, but if you’re looking for forward, all-out American crunch from a Princeton, it might not get much better.

What changes did you notice when you add the 470K? Ive got a 12" Eminence GA-SC64 sitting next to me waiting for the cabinet to come in.

[Colossal]

I put a 470K on the PI on my Princeton and it sounds great. What made an equally impressive difference was testing the amp through a Warehouse Veteran 30 speaker. I started with a Warehouse ET65 and that sounded great, but if you’re looking for forward, all-out American crunch from a Princeton, it might not get much better.

What changes did you notice when you add the 470K? Ive got a 12" Eminence GA-SC64 sitting next to me waiting for the cabinet to come in.

The grid stopper drops voltage and keeps the cathodyne from getting hit so hard and folding like cheap lawn furniture, producing the horrible frequency doubling effect and nasty distortion. Bigger values will smooth that out without killing any tone. You might try a 1M pot there and dial it in to your taste and then replace the pot with a fixed resistor.

[angelodp]

Looks great, is this a kit or scratch build? Where did you source chassis and parts?

A

[mirage_indigo]

That looks so much neater than mine!

[peckjed]

Looks great, is this a kit or scratch build? Where did you source chassis and parts?

A

It was from Mojotone but I opted to use a few different parts and my own wire (instead of the cloth pushback). I found a princeton reverb labeled faceplate on ebay which should be a nice finishing touch!

[peckjed]

I put a 470K on the PI on my Princeton and it sounds great. What made an equally impressive difference was testing the amp through a Warehouse Veteran 30 speaker. I started with a Warehouse ET65 and that sounded great, but if you’re looking for forward, all-out American crunch from a Princeton, it might not get much better.

What changes did you notice when you add the 470K? Ive got a 12" Eminence GA-SC64 sitting next to me waiting for the cabinet to come in.

The grid stopper drops voltage and keeps the cathodyne from getting hit so hard and folding like cheap lawn furniture, producing the horrible frequency doubling effect and nasty distortion. Bigger values will smooth that out without killing any tone. You might try a 1M pot there and dial it in to your taste and then replace the pot with a fixed resistor.

I added the 470K to the PI which made a nice difference. I also added the 1.5K and 470ohm screen resistor and grid stoppers to the 6v6's. Based on Robs layout (https://robrobinette.com/images/Guitar/ ... t_Mods.png) does it matter which end the wire connects to the grid on pin 1 or 5?

[peckjed]

Another thing I noticed - my mid pot is right back near the 6V6's and the wire seems to be VERY sensitive to position and causes some crazy oscillation when when the volume and mid are dimed. Would it make sense, or even help, to put it perhaps behind v1? (im using the external speaker jack for a negative feedback switch)

[peckjed]

Just as an update: based on Rob’s suggested Princeton Reverb mods I added the grid stopper to the PI, and grid stoppers and screen resistors to the power tubes. I also moved the Mid knob over to reverb pedal spot (didn’t have that hooked up anyway - reverb is always on). That seems to have solved my oscillation issue.

I reached out to mojotone to see if their transformers had the power to use 6l6’s and was responded to with this: Your total filament current draw using 6L6's in the Princeton Reverb would be 1.2 for the preamp tubes and 1.8 for the 6L6's, for a total of 3A under normal conditions and the operational peak of the filament secondary is 4A. So, yes you could run 6L6's in the Princeton Reverb with no issues. Hope this helps.

Updated gut shot!

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[pompeiisneaks]

Very cool! Just make sure to be ready to adjust the bias circuit a bit if you want it to support 6V6 and 6L6 as they have quite different bias points.

~Phil

[ViperDoc]

Nice mid pot location. What value did you choose for your resistor to ground and pot?

[peckjed]

Nice mid pot location. What value did you choose for your resistor to ground and pot?

its a 50K linear pot with a 6.8K resistor. When the pot is on 1 its effectively stock and when cranked it adds a lot of overdrive effectively bypassing the tonestack.