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I'm working on a 135 watt Twin Reverb. I recapped it and installed a preamp out jack
as per the customers request. Also the reverb wasn't working.
Troubleshooting the reverb.
I can hear the crash if I shake the tank but, otherwise the reveb isn't working.
I tried another known good tank, different cables and swapped the tube. I clipped in a known good transformer. Nothing brought the reverb back. I tried injecting signal at the grid of the reverb driver tube and heard nothing except the local spanish station which didn't get louder if I turned up the reverb. All voltages around the driver tube were close to spec. I measured a 5 volt drop across the cathode resistor. Around 16 volts across the reverb transformer primary. I tried clipping a 500pf cap across the one that couples the output of the channel to the driver grids. I checked continuity between the caps back to the plate of the preceding stage.
When I checked the voltage at the driver plates I could hear a pop and reverb if I turned the reverb up and touched the voltage probe to the plate, the reverb got louder.
I think the transformer and tank are OK. The driver tube seems to be conducting. But signal isn't getting to the grid of the tube...although if I touch the grid there is no pop, just the mexican music that doesn't get louder if I turn up the reverb.
I'm stumped. Any help is appreciated. Hope that all made sense, I'm tired.
as per the customers request. Also the reverb wasn't working.
Troubleshooting the reverb.
I can hear the crash if I shake the tank but, otherwise the reveb isn't working.
I tried another known good tank, different cables and swapped the tube. I clipped in a known good transformer. Nothing brought the reverb back. I tried injecting signal at the grid of the reverb driver tube and heard nothing except the local spanish station which didn't get louder if I turned up the reverb. All voltages around the driver tube were close to spec. I measured a 5 volt drop across the cathode resistor. Around 16 volts across the reverb transformer primary. I tried clipping a 500pf cap across the one that couples the output of the channel to the driver grids. I checked continuity between the caps back to the plate of the preceding stage.
When I checked the voltage at the driver plates I could hear a pop and reverb if I turned the reverb up and touched the voltage probe to the plate, the reverb got louder.
I think the transformer and tank are OK. The driver tube seems to be conducting. But signal isn't getting to the grid of the tube...although if I touch the grid there is no pop, just the mexican music that doesn't get louder if I turn up the reverb.
I'm stumped. Any help is appreciated. Hope that all made sense, I'm tired.
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