![[-]](https://theultimatetone.com/images/collapse.png "[-]")
10-22-2021, 05:10 PM
Hi Tomi
If all the voltages are high by the same factor then the amp should stay biased reasonably well, except for the detail that the bias filter caps may not be rated properly. However, since someone has been inside the amp previously and boosted all the plate caps, you would expect them to change the bias filters, too.
In any case, this is not normal. I'm not sure if a few shorted turns on the primary would do this (by changing the effective turns ratio from primary to all secondaries), or if such shorted turns would just blow the mains fuse? if this is the fault, then the former is the result and really the PT should be changed. If a heating event could cause this then the insulation on the coil wires and between the windings is suspect. The previous tech should have done this.
Series filter caps without sharing resistors is another disaster waiting to happen.
Bandaids such as a small PT to reduce the incoming voltage only put off the inevitable.
I had a similar seeming incident decades ago. An amp a customer brought over had all too-gihh voltages inside. It turned out my meter had a burnt resistor inside, which once replaced restored the universe to its previous balance.
Have fun
If all the voltages are high by the same factor then the amp should stay biased reasonably well, except for the detail that the bias filter caps may not be rated properly. However, since someone has been inside the amp previously and boosted all the plate caps, you would expect them to change the bias filters, too.
In any case, this is not normal. I'm not sure if a few shorted turns on the primary would do this (by changing the effective turns ratio from primary to all secondaries), or if such shorted turns would just blow the mains fuse? if this is the fault, then the former is the result and really the PT should be changed. If a heating event could cause this then the insulation on the coil wires and between the windings is suspect. The previous tech should have done this.
Series filter caps without sharing resistors is another disaster waiting to happen.
Bandaids such as a small PT to reduce the incoming voltage only put off the inevitable.
I had a similar seeming incident decades ago. An amp a customer brought over had all too-gihh voltages inside. It turned out my meter had a burnt resistor inside, which once replaced restored the universe to its previous balance.
Have fun
