Princeton Reveb New Build.

[Rogerio]

Hy Guys,
First of all I'd like to say that I could've never been able to build this amps if not for the factastic info I found here, thank you all so much for your valued experience. I've just compleated my Blackface Princeton Reverb build, the amp is sounding ok but I have a few issues I'd like to address and resolve:

1. Too much reverb, with the reveb pot set at 3 it has way too much reverb. I've replaced the 3.3M resistor to 2.2M it's still too much, I'd like to bring it down a bit more. I'm using a three spring reverb which I like a lot. BTW the tube is a 12AT7 as shown in the schematic.
2. I incorporated the Paul C and Stokes mods to the PI and power supply, the amps now has some hiss that I'd like to get rid of. I also feel that the bass response is not the same as before these mods, it had a bit more bass defenission before.
3. Sounds very good up to volume 5/6 clean clear sound, if I add more volume, say 7, 8, 9, the sound becomes distorted, not as clean clear sound as before. Could this be because of the PI mods ?

Hope you guys can help resolve these issues, for now !!!!!!

Roger

[MWJB]

1 - look to reduce the value of the 1Meg resistor that is the grid load for the 12AT7, you could even install a pot & call it a dwell control (sometimes necessary with long decay 3 spring tanks).

2 - See if removing the mod affects the hiss?

3 - Distortion at high volumes is to be expected, if you don't think the distortion sounds pleasant, or typical, then we might need to investigate further (supply dc voltage readings). Depending on the B+ voltage the amp might make somewhere around the mid teens Wattage-wise, before distortion - quick test - connect a AC RMS voltmeter accross the speaker terminals & play the amp, try and determine an average voltage at max clean volume & report back.

[Bruce / Mission Amps]

Personally, I would never use a 2m2 resistor in the mixing stage of this amp.
Try; a 3m9 to 4m3 resistor instead of the 3m3 and do not use anything mare then a 10pF cap across it, set the bias of the 12AT7 reverb driver tube with at least a 2k2 to 2k7 resistor, with no cathode bypass cap on it and use a 50K pot for the actual reverb level pot.

[Rogerio]

Hi guys, I've reversed the PI mod, it's now stock as per the circuit AA1164, I've also replaced the resistor back to 3M3, the only mod I kept is the wire feeding the four 100K resistors, that is connected direct to the 18K/2W resistor on the cap can. The amp sounds much better now, to me anyways. It's got the body and bottom I like, the overall tone is much more fuller, there is also much less hiss then before, I'm talking about the volume now at about 8 / 9, there is still some hiss, but I guess that's normal. As for the reverb, I don't quite know how to tackle Bruce's advise. I've already tried replacing the 100K reverb pot for a 50K, that did not seem to work, but I've not removed the cathode cap, as for the 2K2 or 2K7 resistor, I'm using 2K2 as per the schematic. I've also tested the output voltage, it reads 12.5V ac, before it starts distorting.