'67 Ampeg Jet, no trem & high voltage

[flythair1]

Hello MEF Community,

I have a J-12D (6BK11's & 7591's. The 6BK11's are replaced with NOS 6K11/6Q11's) that seems to play fine except for the lack of the trem effect. I have jumpered over every coupling & cathode cap with the same sizes (one at a time) and none made a difference. I tried to test the resistors (in circuit) in the V1 trem circuit, and all seemed ok. The combo switch & trem control checks out ok.

The schematic on the inside of the back cover shows 175v on one plate (pin 10) of V1 and 2v on the respective cathode (pin4). I measured these pins and got very high voltage readings, 385v & 11v.

Can anyone give me an idea where to start to look for the problem? Could one of the large resistors or a filter cap be the cause? There could be some hum with the volume above 5 or so. The PA cathode cap, 20uf X 25v, measures close to spec.

This amp has had nothing changed or replaced except the pre-amp tubes. I still have one of the original 6BK11's and I tried that in V1 also with no difference.

Any ideas would be appreciated.
The J-12D drawing is at Schematic Heaven.

Scott

[MWJB]

385v on the plate of V1 sounds like almost full B+ there...high cathode voltage suggests a drifted/open cathode resistor or tenuous ground connection/dodgy trem switch (not shrting the ground connection).