Vox AC30C2

[pnut5150]

Amp lights up but has no sound, all tubes are lit, but the heater fuse is reading -volts. The fuse is good, I have no schematic on this one. Any help?

[Enzo]

The tube heaters light up? Then the heater fuse is OK and the heater voltages are OK. Lighting the heaters is evidence it works.

Plug a different speaker cab into this amp chassis, use the EXTERNAL jack that mutes the internal, any help? Also flip the impedance selector switch back and forth a couple time to clear it. Does either setting now work?

Remember the high voltages in the amp can KILL YOU, so be careful. Are the high voltages present at the tubes? There is a high voltage fuse inside the amp, right next to the red wires.

[pnut5150]

The tube heaters light up? Then the heater fuse is OK and the heater voltages are OK. Lighting the heaters is evidence it works.

Plug a different speaker cab into this amp chassis, use the EXTERNAL jack that mutes the internal, any help? Also flip the impedance selector switch back and forth a couple time to clear it. Does either setting now work?

Remember the high voltages in the amp can KILL YOU, so be careful. Are the high voltages present at the tubes? There is a high voltage fuse inside the amp, right next to the red wires.

Thanks for reply Enzo. I have hooked up external cab, and I do have 300+ volts at power tubes. If I run pre-amp into another amp, I can hear the cable noise when I touch the cable with my hand, and adjust the volume with that noise. Nothing with guitar plugged in, not even a reverb crash. I checked the screens, is there anything that could be muted? Pretty sure OT is good cause I can hear the popping noises?

[pnut5150]

Could the tremolo have it muted?

[pnut5150]

I have sound now, but it is real fizzy sounding and not as loud as it should be. Seems like half power, and notes won't sustain from guitar, they die out really fast. Any help?

[Mick Bailey]

With the FX loop enabled you can put a signal into the return side and check the output stage is working correctly. You need to establish this first of all to help with further diagnosis.

The sound you describe can be down to a bad PI tube or faulty output tube. You say you checked the screens - did you measure the voltage on the socket of each tube?

Also, there's a problem I've encountered with some of these amps where the wire spring strain relief on the speaker plug shorts out the tip connection - there's no insulating sleeve present and the spring vibrates.

[pnut5150]

Pretty certain it is a pi problem. New power and preamp tubes, no sound from effects loop return. Voltages on pi are
Pin 1: 114v
Pin 2: -004.2mv
Pin 3: 1.032v
Pin 4: 3.265v
Pin 5: 3.250v
Pin 6: 120.6v
Pin 7: -004.2mv
Pin 8: 1.020v
Pin 9: 2.964v
Touching pin 7 with meter probe creates a lot of static and noise though speakers. Also if you touch any component on pre/power amp circuit boards, you will get a microphonic sound.

[pnut5150]

Preamp tube closet to input jack is phase inverter right?

[Mick Bailey]

Preamp tube closet to input jack is phase inverter right?

PI is closest to power tubes.

[pnut5150]

Ok, I'll post some more voltages then. I was on the wrong tube.

[pnut5150]

Pin 1: 218v
Pin 2: voltages jumps between 8.5-9.5v
Pin 3: voltages jump between 11.5-12.5v
Pin 4: 3.344v
Pin 5: 3.334v
Pin 6: 211v
Pin 7: 9.96v
Pin 8: jumps between 15.00-15.5v
Pin 9: -3.050v

[pnut5150]

Ok, I have a schematic now, not really good at them. Anyone else have one they can trace through with me? I replaced pi tube socket, I still have some volume, just not not like it should be. Real fizzy and master volume does not work as it should. Nothing from the effects loop side either. Please help!!!!!!

[g1]

Those voltages do not look right for the phase splitter. You should have around 60V on one side of R55.

Edit: removed link to incorrect schematic

[pnut5150]

Thanks for the reply, I noticed the schematic you posted is a "cc2" mine is just a c2. I cannot find r24 or r25 on board anywhere, unless they are on fx loop board

[g1]

Please upload the schematic you have.