I have an intermittent problem with my TA-15 head. The problem appears to only happen on Channel 2 in 15W and 25W power modes, and seems to be less problematic or non-existent in 5W mode. It typically happens after the amp has been in use for 30 minutes or longer. The gain will suddenly drop very significantly while I am playing. Typical settings are gain at 2:00 and master at 9:00. Tone controls all around 12:00. Problem happens in all Channel 2 modes – Tweed, Hi1 and Hi2. The problem is not accompanied by any unusual noise or microphonics, just a sudden gain drop. Gain typically returns to normal if I allow the amp to cool for a few hours and then turn it back on, but will again drift after around 30 minutes of playing.
I have not yet tried to replace or rotate any pre-amp or power tubes, as the problem that I am experiencing does not seem to be consistent with the manual’s description of typical power or preamp tube problems. Would appreciate some feedback from other users who may have experienced this problem, or from do-it-yourselfers that have repaired these amps. I bought the amp here in Hong Kong and warranty is already expired, repair services here are questionable, so I am motivated to fix it myself if I can.
I have not yet tried to replace or rotate any pre-amp or power tubes, as the problem that I am experiencing does not seem to be consistent with the manual’s description of typical power or preamp tube problems. Would appreciate some feedback from other users who may have experienced this problem, or from do-it-yourselfers that have repaired these amps. I bought the amp here in Hong Kong and warranty is already expired, repair services here are questionable, so I am motivated to fix it myself if I can.