hey guys, i'm looking at a friend's 59 bassman reissue. everything seems to work fine, but V4 red plates and emits a burning smell within 5 minutes of turning it on. first thing i tried was testing the old ones. (i tested all of the tubes. pre's and rectifier good.) V5 tested almost new, V4 tested almost dead. i put in a used but known-good pair and turned the amp back on looking for clues and checking voltages. V4 started glowing cherry red. weird thing is, all the voltages seem great (except one) and plate and grid resistors are fine.
the only discrepancy i found was on pin 3. according to the schem, it should be about 257v. but this one reads at about 450v! actually, pin 4 and pin 3 on BOTH power tubes are reading the same voltage.
so, i'm wondering...why is V4 getting taken out and NOT V5? if all of my components are seemingly fine, why is this happening? could it have anything to do w/ the OT? definitely need some help w/ this.
thanks!
the only discrepancy i found was on pin 3. according to the schem, it should be about 257v. but this one reads at about 450v! actually, pin 4 and pin 3 on BOTH power tubes are reading the same voltage.
so, i'm wondering...why is V4 getting taken out and NOT V5? if all of my components are seemingly fine, why is this happening? could it have anything to do w/ the OT? definitely need some help w/ this.
thanks!
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