1961 Ampeg Revererocket R12R tremolo not working.

[jvm]

I have a 1961 R12R Ampeg that works great except for the tremolo. The amp has been previously recapped including the four caps in the oscillator circuit. All trem circuit resistors are good. I subbed a new 6SL7. V1B voltages are 117v at the plate and .85v at the cathode. The foot switch is working as I can see the oscillator start when switching the tremolo on. I monitor the voltage at the wiper of the intensity pot. When the foot switch is engaged the wiper sees about 17 volts which drops immediately to 0 volts. My oscillator is turning on but not staying on, correct? V1B voltages are 117v at the plate and .85v at the cathode. Anybody have any suggestions?

[Jazz P Bass]

Bad schematic link.

[jvm]

Sorry, Jazz. I added a image of the original schematic. It seems to be opening.

[Leo_Gnardo]

There's three caps in the oscillator, plus another one carries its output wave to the depth pot, plus there's a cathode bypass cap on the triode. Weakness/failure in any will put a stop to your tremolo. There's also a habit of old hi value resistors to fail, so be sure to check those. I find it pays to use good quality caps for instance Mallory 150, Panasonic or Xicon metallized polypro, or "orange drops" to assure oscillator function.

When was the amp re capped? If it was a long time ago say 20+ years it may be time to swap in some newer parts at least in the trem circuit.

[jvm]

The amp was capped within the last several years with orange drops. They all show the proper value with my capacitance meter. I have tested all the resistors in the trem circuit and replaced a couple that were out of tolerance. Both pots test good. I changed the cathode cap and now have a reading of 3.6v at the intensity pot wiper where I had .85v before changing the cap. Voltage jumps to about 18 volts and then drops to zero when foot switch is activated. My plate voltage at Pin 2 is 323v with trem off and 111v with trem switched on.

[jvm]

Problem solved! I traced out the circuit and discovered that the .1uF cap had been installed in the wrong eyelet. It was installed across the 270k plate resistor! tremolo is working great now! Thanks for your help guys!