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TSE: what did I blow up?

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One channel of my TSE is sick :(

I moved it from breadboard to case, and while I was doing this, somehow one pin of the DHT socket came loose. Pretty sure it was the filament pin, so I powered up the amp with the filament pin floating with no connection to the output tx.
I powered up the amp a few times in this condition, but only for a short time.

I fixed that, but now when I apply power the bias voltage on that side shoots up, so I shut it down.

I tried different driver tubes and DHT's, so pretty sure those are OK.

I still need to inspect the passives, but assuming I don't find a charred resistor my guess is that Q1 blew, and needs to be replaced.

There's not much here that could have broke.

Any advice to get my TSE back up and running would be appreciated.

Randy
 
I fixed that, but now when I apply power the bias voltage on that side shoots up, so I shut it down. ...

If by "shooting up" you mean becoming increasingly negative, it should just cut the power tube off, so should not damage anything while you troubleshoot.

My WAG is the MOSFET on that side, OR a bad solder connection in that area that got boogered up when you moved the board to the case.
 
First off, remove the output tubes to avoid the possibility of damage. If the grid voltage is highly positive and does not adjust, the associated mosfet is likely shorted. Even a microsecond momentary short on the grid of the output tube will blow the fet.

After replacing the fet the voltage should adjust through a range of negative voltages. Once that's working, then reinstall the output tubes and set bias.
 
So here is what happened.
I took my amp apart, and replaced Q1 and Q2.
After replacing them, I noticed a short between two pins on one of the DHT sockets, a solder bridge. I think I created the short when I fixed the loose socket, and didn't ohm out for shorts.
Pretty sure that was really my problem.

I put everything back together, and then I was not getting b-. Took apart again, and found an open R5. Luckily I had a spare, so fixed, put it all back together, and after one other self induced problem, I get sound again.

So other then an open R5, which did not look damaged, all my problems have been workmanship, which I normally am very careful with, I guess my work is getting shody as I get older :)
 
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