Sano 300R Tremolo Problem

[rf7]

This amp closely resembles the 50WRT & 30WRT schematic that's linked below. The tremolo does not work.

I pulled the power tubes out to work on the amp without having to hear my test tone thru the speaker. I replaced a JFET and the cathode capacitor to get the trem to work in the preamp. So far, so good. When I plug in the power tubes, then the trem goes away. If I pull the phase splitter and the other 12AU7 in the power amp section (page 2 of the schematic), and leave in the power tubes, then the trem works in the preamp.

All of this is taking place whether or not the preamp output is connected to the power amp section. Note that the B+ throughout the amp drops down whenever the full tube complement is installed. The filter caps are original, but the power supply ripple looks fine. I'm thinking that maybe the power supply can't supply enough current for the tremolo to run. Any suggestions?

sano 30 50 wrt amplifier schematic Download page :: Schematics Unlimited

[g1]

It could also be that there is something wrong in the trem. circuit, and boosting the B+ above normal is masking the fault. I'd be more inclined to believe that than think that low B+ is causing the fault.
As this may not be the exact schematic, it's hard to say if you should be getting the 500V shown at the rectifier. What kind of B+ do you have?

[Jazz P Bass]

Maybe you could monitor thr Tremelo tube voltages & see 'why' it is quitting.

[Enzo]

In the trem circuit I see a pair of .05uf, a 0.02uf and a 0.1uf cap, not to mention the cathode bypass 2uf cap. Are those fresh and new? If anything is voltage sensitive in that circuit, those would be it, in my view.

[rf7]

I replaced all of the trem caps and it still does not function with all tubes inserted. I changed the trem Oscillator plate resistor to match the schematic, as the plate voltage was sitting at 65V. The plate resistor was 470K, but now it is 330K, which brings the plate voltage up to 98V, but the trem is still dead with all tubes in place.

The B+ is at 348V with all of the tubes in, whereas it sits at 410V with the power tubes removed. It's still a far cry away from the 500V on the schematic.