Core32
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Well obviously something is wrong. :o I don't exactly understand your voltage readings. If you measure AC volts, putting the meter probes one each at the end of the transformer brown wires, not on ground, you should see about 6.3V. You can do this easier by pulling tubes and placing one probe on pin 4 and the other on pin 5 on each socket. Based on your readings I assume you are reading from ground/chassis to one brown wire end and on the good amp get 3.3V on one wire and 3.7V on the other. If the AC on each pair of heater pins is at about 6.3V AC, then I would measure the following pattern (all the following are now DC measurements): With all tubes out of the sockets, measure DC volts, on pin 4 to ground and then pin 5 to ground and do this for all three sockets, six measurements total. If any of these measurements is any more than a volt DC there is a problem. If all 6 measurements are in the millivolt range (zero volts DC is good too) then put any one tube back in. Again measure DC on pin 4 to ground and pin 5 to ground of the remaining two empty sockets. Any significant DC voltage shows a problem. If all is good then add a second tube back in. Repeat the measurements for pins 4 and 5 of the remaining empty socket. If all is still good, put the third tube back in and pull either of the other tubes back out and measure pins 4 and 5 again of that newly empty socket. This should be a pretty good test of the heater wiring and the tubes themselves for internal shorts. HTH.
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