I purchased a used R8 without driver tubes. Tonight I installed a new quad of KT88's. Volume turned all the way down and powered it up. After about 5 seconds I got a very loud squeal from the right channel. I turned the power off and the squeal faded away. I disconnected all the inputs and tried again. Same story left channel is silent and right channel produces a scary loud squeal. Speakers are Klipschorn's. Any ideas? Swap V1 V2 and V3 V4? I have an old set of EL34'S I could try. I don't suspect input tubes since volume is all the way down. 30 day warranty just send it back maybe...
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Finally got around to swapping all of the tubes around. It was one of the NEW KT88's. I'm contacting the vendor to see if they want to swap the quad or replace with another one that measures the same. At least I'm able to listen with an old set of EL34's I have left from an old ST70. Thanks for all the help!
I"ll try that today. This is happening with the volume all the way down. I guess I need to look and see where the pot falls in the schematic.
Did you try swapping all the L/R channel tubes? Try the front 6SL7s, if no change swap the 6SN7s, still no change then swap the KT88s. If the squeal switches side then swap just one KT88 to determine which tube is the problem. If swaping tubes achieves nothing, then it must be something internal failing - I would look at the Willsenton branded caps first.