Rivera Pubster 45 nose problems - advice needed

[nresnik]

Hi!
I need help.
I own Rivera Pubster 45.

The amp works perfectly, quiet, no hum, buzz, nothing.
Only sometimes, when i engage amp from standby (hit tubes with voltage), it starts to crackle and hiss, loses power and it persists, no matter if I turn it on, off, put it to standby repeatedely. Usually it cures by itself after a day or two, but ih happens regardless the amp is warm or hot.
A few days ago it happened again during the rehearsal when I put standby to ON, but this time when I turned the master volume and it stopped immediately.

I took it to my amp guy, as always when this happens, an d as always, he examined the voltages, the tubes, the gr oundings, contacts, transformers... everything in perfec t shape.
But, this time he said, since the crackling and hissing and power loss stopped immediately after I turned the Master voliume, that in his opinion the only thing left that could be the cause are one of the FET transistors IFN6449.
Since I live in Croatia and there is no Rivera service a nywhere near, please can you give me your opinion if it could be the FET related problem?

Nenad Resnik
Varazin, Croatia

[Jon Snell]

Check your effects send and return sockets, plug another amplifier from the send to an input and monitor what is going on.
Those FETs are awfully expensive, try swapping them over but lift C104 first to check it is Q101 or not.
They normally fail, not go noisy.

[xtian]

The standby switch itself is suspect. You can just jumper across the switch temporarily to see if this solves the issue.

[Mick Bailey]

Did your tech clean and lubricate the master volume pot?