Crate Vintage Club 50 "cutting out".

[PoPo75]

My Crate VC50 just recently started cutting out. It will sound great for about 20 minutes or so then will cut to about 1/2 volume/gain. Then it will come back then go out again. I'm thinking it needs tubes. I've had the amp over 10 years at least.

My question is can I replace the tubes without re-biasing the amp?

Or could this problem be caused by something else?

[Jazz P Bass]

The FX jack may be dirty if you do not use it.
The preamp to power amp signal runs through the jack on a normally closed contact.
Try running a cord in & out of the jack rapidly.(power off)
If that seems to help then you need to clean the jack properly or replace it.
It is a TRS setup.

[PoPo75]

The FX jack may be dirty if you do not use it.
The preamp to power amp signal runs through the jack on a normally closed contact.
Try running a cord in & out of the jack rapidly.(power off)
If that seems to help then you need to clean the jack properly or replace it.
It is a TRS setup.

Hmmmm.... I have NEVER used the FX jack. That could be it. I will try it. Thanks!

[Pedro Vecino]

My question is can I replace the tubes without re-biasing the amp?

This amplifier has a serious problem with the bias circuit. Voltage (-15 volts approx.) is taken from a circuit which does not allow increase it. At least I have not found the system to do.
With this voltage the natural tendency is that the tubes are extremely hot. Now I have one, and a quartet of EL84 EH standard (medium grade) consumes 38mA per tube (14 watts dissipation) measured across its plates.
The solution I've been using a long time with this amp is to build a separate bias circuit taken from the HT line. With it you can adjust perfectly any EL84 set.