Rockford Fosgate Signature Phono preamp

Thank you.  

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.

"The Fosgate does not have left and right channel tubes. Each of the 6 audio tubes does both channels."

Melm's post echos my thoughts, which is why I in my previous post you need 3 individual tubes. I doubt it's a tube.

If there were no output- both L/R, then switching tubes would work.