Princeton Reverb ... tweaking

[Deric]

I've started ordering parts for a Princeton Reverb (AA1164) build. So far, I plan on a straight up build with only a few changes:

- Raw control
- Adjustable bias
- Bias test points

I've seen a simple cross-line MV used. Anyone here tried it? Not too worried about turning it down but if it's effective it could be nice around the house.

Ordered a chassis and iron from Mojo. Any suggestions for coupling/tone caps? I have lots of 6PS and Mallory 150's on hand but was thinking about trying the Sozo blues....any tried these? Opinions?

Any other suggestions/comments/tips etc??

Thanks,
Deric

[Big Jim]

Hi Deric,
A Princeton reverb is on my hit list as well. Sonic goodness 'ala Mike Campbell! Hard to beat. I just built the sweetest lil Tweed Deluxe using the Sozo Blue molded caps. I'm really happpy with the sound of the amp. The Blues are supposed to mimick the old Astrons to a T. John Gaynor told me that they are hand made in his shop one at a time. He doesn't distribute his high end caps to dealers, so if you decide to use them, they have to be ordered from his website. Nice guy, great products.
Jim

[Colossal]

I used Sozo Blue Moldeds throughout (for both tone and coupling caps) for a jazz amp build and it sounds fantastic. I plan to use them again. They definitely sweetened up after some hours on them. Very clear and musical sounding. Good luck with your Princeton build.

[Deric]

Thanks for the input. I was about to order some but considering the price and the fact have lots of other caps laying around I figured I'd get some input first. Looks like I'll give them a shot.

[tubeswell]

FWIW I did my BFPR with a mosfet (IRF820) source follower in the LFO circuit, which gives the trem a bit more effective slam. I also used separate filter caps (instead of a cap can) and the grounding method outlined in Merlin's article here: http://valvewizard2.webs.com/Grounding.pdf

[Alexo]

I found it really useful to make the nfb adjustable in my PR clones. Pretty simple to just stick a 10K click pot on the back for this purpose.

I've used old PIO caps and 715P's in this amp, both sound great.

Have fun!

[Deric]

Tubeswell - Thanks for the tip on the trem. I'll probably build it stock first and see what I think. I haven't had an amp with tremolo since I sold my Twin 13 years ago....

Alexo - By "click pot" do you mean a detented pot or a click on-off kind of thing?

Thanks for the input guys. Parts should start showing up this week.

[Deric]

Just finished this up yesterday. Worked perfect on the first try (that's a nice change ) and sounds great!!!

Got a cab from Mojo with the baffle cut for a 12" speaker. Threw in a Hellatone 30 (only speaker I had laying around...) and it sounds like a nice match.

Would like to tame the 'verb a bit. I've read that an audio taper pot helps so I may try that.

Also think I'll add a pot for variable negative feedback. Was thinking of just sticking a 25k pot in line with stock 2k7 resistor. Comment? May also add a switch to drop the bypass cap on V1a to 5uf or so to tighten up the low end when cranked.

[tubeswell]

The 'best' way to tame the verb is to either increase the 470k resistor (incrementally) or decrease the level pot (50k) or both IMHO. (You could try a 50k level pot and a 560k resistor to start with).

You also can decrease the 3M3, but beware that that starts to give more of a BFP vibe because the dry signal would also be 'beefed up' in that case. The 3M3/(470k+100k) is a voltage divider that attenuates the dry signal to between 570k/(3M3 + 570k) = 14.7% of its strength on a 'fully wet' signal or 3M3/(3M3+470k) = 12.5% of its strength on a 'fully dry' signal - compared to if you just hooked the TS recovery stage's output coupling cap up to the next stage. (On the other hand, you may like more dry signal drive?).

[Deric]

I have played with dropping the 3M3 resistor to 2M2. Seems it increased the gain (in a good way) more than changed the 'verb.

I'll try tacking a 100K across the Reverb pot and see what that does for starters.

Thanks for the input!!

[Normster]

What tank are you using? On a recent AB763 build, the 4AB3C1B was way too much for my taste, but an 8AB2C1B was just about right. You can also add a dwell control if there's too much "tail" on the reverb. Just replace the 1M grid load with a trimmer. Run the cap to the input, wiper to grid, and bottom leg to ground.

BTW, I'm building a BFPR into an old Crate combo for a friend. Can't wait to see how it turns out.

[Deric]

Thanks Norm!! Any idea where to find that tank?

[Deric]

With 2 bypass caps (V1a) in series can you short one (I'm guessing the one connected to ground) without a "pop"?

Tacked a 100k resistor across the Reverb pot and it's much better. Still think I need a tank with a shorter decay....

Getting closer!

[Structo]

Got any pictures Deric?

[Firestorm]

One classic fix for a reverby blackface is to replace the 12AT7 driver with 12AU7.