VOX AC30/6 TB problem

My first post so hopefully in the correct forum? Also I have searched VOX related topics but can't find my particular issue.

The issue is with my VOXAC30/6 TB (KORG) that I bought new in 1994.

Some while ago the sound output on the brilliant channel was very noisy and crackling so I replaced the volume control pot. This seemed to fix the fault but it then came back on an intermittent basis, but the amp was "playable".

I haven't used the amp in ages but this week I thought I would check it out.
The very noisy brilliant channel is still just as loud and now there is no sound output from any channel when I plug in a guitar, and no loud hum from touching the end of the jack plug.

I have checked all of the valves/tubes by substitution one by one to eliminate that possibility with the exception of the GZ34. I've measured this with a multi-meter and it seems to check out OK.

I have downloaded the circuit diagram for this model but nothing jumps out as obvious. I'm assuming the sound output stage is OK by the sheer volume of noise from the brilliant channel, so maybe I should be looking at the pre-amp stage?

If anyone is familiar with this Vox model and circuitry I would really appreciate any guidance or suggestions.

Many thanks, James.

I think I may have found the problem! It must be a dry joint on the board or a badly soldered wire!

I just inverted the chassis to measure voltages around the valve bases and when I switched on everything works, nice and loud and no crackling from the brilliant channel.

I'm now going to take the board off of the chassis and inspect for bad joints.

Inspect and re-tension all the preamp tube socket contacts.

Beam Tetrode":21wljdtv said:

Inspect and re-tension all the preamp tube socket contacts.

Click to expand...

I've separated the circuit board from the chassis and I'm working my way through the soldered connections. So far nothing has visually stood out as being suspect even when "wobbling" the soldered wires, and the factory soldered components all seem to be OK too.

I will now take Beam Tetrode's advice and inspect and re-tension the pre-amp tube sockets.

Many thanks, James.

Valve and tube sockets all inspected and re-tensioned.
It must have been the problem because the amp is now working perfectly.

Having the amp stripped down made the perfect opportunity to deep clean the case fabric, handles etc. It now looks brand new again.

Thanks again,
James.