Unique problem - one channel silent under different variables

Hi Denis,

As you’ve surmised, it sounds like the preamp has a problem that needs to be sorted out via professional troubleshooting. The symptoms you’ve described don’t point to any specific cause, as far as I can tell.

But as Jond indicated it sounds like you are not following the proper turn-on and turn-off sequences (with the power amps being turned on last and off first). Also, it sounds like you are disconnecting and reconnecting the RCA cables that connect the preamp to the amps while everything is powered up, which is definitely bad practice and could conceivably damage your speakers.

That said, I wonder if disconnecting the RCA cables and then re-connecting them WITHOUT switching the channels would have the same effect as what you have observed when you disconnected and re-connected them with the channels reversed. It could be that the channel reversal was not what restored normal operation, but rather a transient of some sort caused by the disconnection and reconnection itself, that might have temporarily zapped the defective preamp circuit back into normal operation.

Or if the problem is temporarily fixed only if the channels are reversed when the cables are disconnected and reconnected, that may just be due to the happenstance of the resulting transient being different when the reconnection for the problematic channel is made to a different amp than previously.

Good luck. Regards,
-- Al

I learned 20 years ago to  turn amp on last, off first. What makes you think I do all these cord exchanges with power on? Did I say that? No, I think you assumed it. With due respect, and I know you are being helpful, if I haven't learned that basic, I shouldn't be  wasting your time posting. Thanks for your input,
Denis

Al,
Thanks for your thoughts. I have found that if I leave the preamp on constant standby, the issue is resolved. It seems that the unit/tubes/caps/resistors work if kept "warm". Forgive my indignation at the thought of doing anything with power on! To me that's like driving s car with the hand brake on or playing with the innards of a 1500 w amp with the unit on and plugged in :)

It could be that one of the connectors on the cable is a little tighter than the other and one of the RCA jacks on the preamp is a little looser than the other.

When the right combination is used everything is fine, but if the (2) wrong ones are used, you drop a channel.

Maybe try a different set of cables from preamp to amp and see what happens.

Might be a problem with the left channel amp. Swap the left and right speaker cables and see if the trouble moves to the right channel.