Ampeg SVT CL voltage question

[Dan Mc]

I am working on a SVT CL - oh the joy. Bias voltage is off. I only get -130vdc where schematic shows -180vdc after rectifiers and filtering. Anyone roughly know what the AC voltage should be on the secondaries from the filament transformers. Plate voltage looks good as does screen voltage

thanks in advance
Dan

[Enzo]

180v? It is a simple rectifier, so I'd expect about 130vAC. And I suspect if you measure the ripple on your -130v you will find it substantial. it is supremely unlikely your transformer started making the wrong voltage. It is not unlikely at all that C23 is not doing its job. Try looking into that.

I suppose it is also possible a tube failure at either the cathode follower drive tube or even a bad power tube could be dragging it down. Pull the tubes and see if it comes up.

[Dan Mc]

That reading is with no power tubes. Tried new driverswith no change. I will try C23 next.

Here is the back story. Amp came in with bias lights both on. Two 6550 blown and shorter screen resistor. Replaced matched sextet 6550 and replaced blown resistors. I also checked usual suspects - and looks good ex pet bias voltage only getting -28vdc to 6550. Preamp stable. With power tubes installed the amp draws about 4 amps at idle with both bias indicators on all and hum on output