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Im new here and at amp repair. I have an issue with my dual showman red knob (non reverb). I just received the amp and started testing it (compu-bias) to find the third tube socket is off. The plate voltage is correct (486), but the cathode current and watts are half what they should be (9 and 4.3). I switched out the tubes and the second set read the same 50% lower on the third tube. Does anyone know what it might be?
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Welcome to the place. There could be many reasons, but the first thing that I would check is the screen grid resistor on that tube socket. -
So I replaced the screen grid resistor and the third tube still reads 9 and 4.3. I'll most likely take it to my amp repair technician, but I'd like to have some idea what the issue is prior to dropping it off. If anyone has an idea what might be causing this I'd like to hear it.Comment
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check the bias voltage on pin 5 is the same as the other valve on that side.
check the screen voltage on pin 4 ditto.
check if there is any voltage on pin 8, which should be grounded.
check the socket for arcing. Rock the valve gently with the amp on to see if you get contact noise
swap the valve with its partner and check again
if it's none of those things it's probably in your measurement method.Comment
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What kind of reading are you getting for the other tubes? 4 watts seems to be much less than half of what it should be.Originally posted by Enzo
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Bad tube. Thanks for the help. The second set I tested had a bad tube as well which was why I thought it was something else. It brings up a new question: can I use 2 6l6wxt and 2 5881wxt (abba)?Comment
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