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33 Posts
Discussion Starter · #1 ·
Hi everyone.

Hoping to get a bit of advice on my amp head, which started humming a few days ago. I'll try and give as much detail as possible to help diagnose.

- It can be heard slightly when on standby then loudly through the cabinet when standby switched off
- Volume controls make no difference to the volume of hum
- Hum increases when overdrive pedal is engaged
- I've checked the power tubes - one is slightly dimmer than the other, but only marginally
- Bias is at full clockwise position (not sure if this is hot or cold. If hot then could the valves have been over powered?)
- Reseated power tubes and switched them round but no change
- Tried different cables and even moved it round the house thinking it could be interference
- Head itself is about 8 years old

It went in for repair 6 months ago after a power tube went (blew some fuses too), so the tubes themselves are only 6 months old with very infrequent use.

Likely hood is that it needs to go for repair again, but if the above are the tell tale signs of power tubes failing I'm happy to replace them myself and re-bias.

Appreciate it almost impossible to diagnose without seeing it in person, but any similar experiences / advice would be fantastic. Thanks for having a look.
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