Isn't that a tube-based preamp? If so, have you checked the tubes?
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Contact Musical Surroundings for an RA#
They will refer you to their repair facility in Maryland. A repair shop can't get a schematic. Unless you really know someone who is capable, it's the only alternative.
My Foz is 8 years old? Still holds up to current stuff. Just not as quiet if you like wide open alot.
If you have the 3 tube types handy, easy enough to swap.12ax7, at7 and 6dj8. My Foz was repaired for a futzy right channel. The finish/assembly quality is subpar as far as clean wiring/soldering. That, and a cap wasn't seated properly in the board.
A year later, the unit became noisey. I popped the lid open to find more sloppy finish work on the right channel that was serviced. Figured it wouldn't hurt to copy the left channel wire dressing and it's back to quiet!
If I was going to check if a tube is my problem, how would I go about checking this out? Which tubes should I swap?Swap the tubes between left and right channels. If the dead channel follows the swap, you know it's a tube.
The Fosgate does not have left and right channel tubes. Each of the 6 audio tubes does both channels. That’s what makes tube-rolling on the Fosgate so easy. (Requires just balanced, not matched, tubes) So if it’s a tube problem, you’ll have to replace each of the tubes in turn.
But, usually IMO, a tube does not just go quickly totally dead, and just on one side. They kind of peter out in one way or another. So my guess is that the problem is elsewhere. Assuming that you have tried it in more than one preamp input and that the tubes are plugged in firmly, the problem is likely elsewhere in the Fosgate.
I’ve run my Fosgate for years without an issue, except for a noisy tube.