Prima Luna Tube Question


Hi - I have a new PL Dialogue Premium HP amp; connecting it to my system out of the box one of the channels did not work (no sound).  I started the troubleshooting process; move the speaker connections and then swapped the gain and driver tubes left to right - in both cases the channel outage followed the left to right swap.   Finally thought I isolated the issue to one of the driver tubes.  

I replaced that tube with a new PL branded 12AU7 tube and I got sound out of the channel, but noticed it was not passing the full signal to the channel (it seemed to be missing the mid range and the stereo imaging was focusing on the other channel).  So I started the troubleshooting again by swapping the tubes across channels to see if the problem followed the tubes - it did.  I eventually got fed up with the troubleshooting and replaced both gain tubes and 2 of the driver tubes with a new set of 12AU7's.  Through this effort, the problem seemed to come and go and resolved itself temporary after resetting the tubes.  

Anyone have ideas on what the potential issue could be?  Am I focusing on replacing/re-seating the wrong tubes?

Thanks - Michael
qpmicro
On the rear panel make sure the stereo mono switch is in the stereo position if you are using the amp as a stereo amp. Its possible the switch got bumped or moved during transport or unpacking.

If the switch is ok, have you tried swapping cables from channel 1 to 2?

best
I did confirm the stereo/mono switch was correct in my initial troubleshooting.  The IC's were swapped and the issue followed the channel.  

Thanks - Michael
Buy some vintage USA-made tubes: GE, RCA, Sylvania, KenRad, Hytron, National, Tungsol. I prefer these for the 12A*7 and 6S*7 series. Superior quality (lower distortion and longer life) than current Communist production! And I use US made vintage tube amps!
If the amp is new, the tubes are covered under warranty. Call your dealer and have him get you new tubes at no charge.  It could also be a bad cable,  try a different pair.  You mentioned when you swapped cables, the problem went to the other channel.  That tells me it’s the cable.