Princeton Reverb AA1164 tremolo no working...

[mrdarwin]

Hi there!
I finished a princeton reverb vintage clone. It sounds very nice, evrey thing is ok except tremolo
After two days of unsuccessful investigation, I'm asking for help.
what I'v done:

- double/triple checked wiring
- no footswitch installed, regarding the schematic, tremolo doesn't need footswitch to work.
- installed a bias pot, instead fixed bias circuit. 'Cause I read too hot bias affects tremolo... now the amp is biased at 20mA for 410V plate. Still no tremolo...
- tried 4 differents 12ax7 tubes, and swapped with v3 and v1... no tremolo
- the blue wire to "vibrato pedal" connector is NOT grounded
- here are the voltages on v4: p1: 396v p3: 6.8v p6: 260v p8: 67v

I don't really know what I'm looking for... variation of DC current? AC current somewhere? I read that the tremolo is an oscillator which affects bias current. How can I test the oscillator circuit? v4 p1 is not "swinging"...does it have to "swing"

Thanks!

schem: http://fenderguru.com/wp-content/upload ... layout.jpg

[sluckey]

V4 pins 1, 2, and 3 are the trem oscillator. Pin 1 should be swinging. You can see a smooth swing with a scope or analog meter. The swing just looks like erratic numbers on a digital meter.

Your high pin 1 voltage indicates the tube is not conducting. But your pin 3 voltage is also high which would indicate the tube should be conducting. Maybe you have a wrong value cathode resistor. With power off, measure resistance from pin 3 to chassis. Connect your meter directly to pin 3 on the socket. Reading should be 3300Ω. What have you?

[mrdarwin]

Thanks Sluckey, you point the right direction!
The cathod resistor labeled 3k3 in the package was 3M3... now everything's right.
Finally we can trust only one thing: the digital METER!... and this forum

thanks again

[sluckey]

There is supposed to be a 3M3 resistor in the reverb mixer circuit. ***IF*** you have mistakenly put a 3K3 resistor in that position the reverb will be weak if any. Might be worth verifying there is a 3M3 in that position.

[mrdarwin]

It was the first thing I thinked about... but no. Just one mistake, finally.
Now the amp is running. Thx again!

[Stevem]

The first rule of amp repair and or building is to check every resistor on your meter and get a ESR meter to test every new cap!