Ampeg V4 (VT-22) Troubleshooting
Hello everyone!
I’m having issues with my Ampeg V4 (VT-22), so I'm hoping to get some insight from people with more expertise. I’ve done everything I can think of and exhausted every resource I could find to identify the issue to no avail. I have a limited understanding, so I haven’t been able to narrow things down in a reliable way with troubleshooting.
When I turn the amp on and plug my guitar in, I’m getting no signal until the volume is turned up to around 10 o’clock. It’s distorted with limited sustain (it should produce a clean sound), then drops out completely until I strum again. It’s the same for both inputs, and the ext. amp jack on the back.
The power light is slightly dimmer than the standby light. It was flickering slightly when I initially started working on it, but that has stopped and I’m not sure why. It’s still a bit dim, but solid.
Any advice would be greatly appreciated! Please let me know if any clarification is needed, or if there’s more troubleshooting I can do. I’ve listed everything below.
Tubes:
- 4 x 7027A
- 12AU7
- 12AX7
- 12DW7
- 6CG7 (Missing)
- 12AX7
- 12AX7
- 6K11
All but the 6CG7 and 6K11 have been replaced with brand new JJ tubes. From what I understand, the amp should be working without the 6CG7 tube (reverb), but I’m not certain of this.
Troubleshooting (Tubes):
- Swapped all of the pre-amp tubes with other working tubes
- To test the power amp tubes, I removed 1 and 4 position 7027A tubes, matched impedance and tested amp, then did the same for 2 and 3 position 7027A tubes.
- Fuse has been replaced and I’ve tested multiple (6A/250V)
- I’ve tapped the tubes with a pencil to see if they are microphonic, but none seem to be. I’m not sure how hard I should be tapping them, so I may need to revisit this.
Troubleshooting (Other):
- DeoxIT cleaning of input jacks, ext. amp jacks, speaker jacks, fuse cap. Using a patch cable, inserting and removing around 20 times, twisting in between. As well as a q-tip, which came out quite dirty but I still see some oxidization on the jack tip and everything else. I will try using something abrasive if this could solve the problem.
- I’ve replaced the three prong power cable end, but not the entire cable. It is a bit loose at the base where it connects to the amp, but the power isn’t cutting out, only the guitar signal.
- I ran my guitar through the ext. amp jack with the same result as the front input jacks. Although, I found I could get the same distorted guitar signal at a much lower volume, with the knob around 7 o'clock.
- Obvious troubleshooting, such as cables and guitars have been tested. I’ve tried a different speaker cabinet as well as a different amp and it worked fine.
Thanks again for any advice!