I am in the process of restoring an SVT-6 Pro that was blown. I am a collector of Ampeg gear and have brought back to life several different amps but this one is killing me. I am not an electronics guy, but am a biomed engineer and have a fair degree of technical skills.
I have replaced all of the mosfets, diodes, and resistors on both sides of the power section. I have also replaced all of the transisitors and tested all of the diodes and resistors on the main board. I also replaced IC2, but have not replaced IC1(TLO-74).
I am testing the amp outside of the case on a rubber covered piece of plywood with the preamp completely disconnected. This allows me to have better access to test points. I have only the transformer, switch and fuse attached. I dont know if this matters or not.
The main board powers up just fine, fans spin properly, tubes heat up, big resistors are hot etc. No puffs of smoke or sparks......
With only one set of mosfets in Channel 1 (+) I get -65V on the output. If I adjust AP1, the voltage on the output will increase from approx 30V to 70V DC. There is not increase in the voltage accross the .47 ohm source resistors. Actually there is no voltage at all across the source resistors.
With only Channel 2 (-) I get zero DC voltage on the output, but similarly I get zero voltage across the .47 ohm source resistors when adjusting AP2. There is no heat on any mosfets they do not get warm at all.
Any ideas would be greatly appreciated. You can see that some of the voltages seem a bit off, but nothing is really jumping out at me. I am concerned about IC1 (TLO-74) but I don't want to order one unless advised. I have spare parts for all other silicon parts and resistors.
Thanks a bunch.
I have replaced all of the mosfets, diodes, and resistors on both sides of the power section. I have also replaced all of the transisitors and tested all of the diodes and resistors on the main board. I also replaced IC2, but have not replaced IC1(TLO-74).
I am testing the amp outside of the case on a rubber covered piece of plywood with the preamp completely disconnected. This allows me to have better access to test points. I have only the transformer, switch and fuse attached. I dont know if this matters or not.
The main board powers up just fine, fans spin properly, tubes heat up, big resistors are hot etc. No puffs of smoke or sparks......
With only one set of mosfets in Channel 1 (+) I get -65V on the output. If I adjust AP1, the voltage on the output will increase from approx 30V to 70V DC. There is not increase in the voltage accross the .47 ohm source resistors. Actually there is no voltage at all across the source resistors.
With only Channel 2 (-) I get zero DC voltage on the output, but similarly I get zero voltage across the .47 ohm source resistors when adjusting AP2. There is no heat on any mosfets they do not get warm at all.
Any ideas would be greatly appreciated. You can see that some of the voltages seem a bit off, but nothing is really jumping out at me. I am concerned about IC1 (TLO-74) but I don't want to order one unless advised. I have spare parts for all other silicon parts and resistors.
Thanks a bunch.
