Trace Eliot Velocette 12R preamp heater supply

[Helmholtz]

OK, so measure in series with primary side, and secondary unloaded? As suggested in post #2?

You may, but it won't reveal anything new. With heater circuit disconnected primary current will be low and connecting the heater circuit will increase current. There is no doubt that the PT has no winding short.
If FS4 blows, the problem (short) must be in the following circuitry. Do you get 24VAC at the secondary with FS4 out?

You may want to use a bulb limiter to save fuses.

[log1982]

Message for the OP: I get a sense that you're looking for a quick answer. Who wouldn't? The suggestions from this community are more pragmatic. Each member has made a suggestion that helps isolate the problem, and we expect that to be the first step in a multi step approach. It's a time tested trouble shooting method. I hope that helps you push forward. Let us know what you decide, and what your results are.
Jcon.

[log1982]

I had another thought, and again I'm open to other interpretations. I think TR11 is a current-limit circuit to reduce inrush current. It keeps TR7 healthy during the stressful turn-on requirement of charging the caps and feeding the cold filaments. Having said that, there are a lot of opportunities for a structured troubleshoot methodology. Let us know what you come up with. BTW, is FS4 a slo-blo?
Jcon.

[Dave H]

I had another thought, and again I'm open to other interpretations. I think TR11 is a current-limit circuit to reduce inrush current. It keeps TR7 healthy during the stressful turn-on requirement of charging the caps and feeding the cold filaments. Having said that, there are a lot of opportunities for a structured troubleshoot methodology.

I think that's correct. Perhaps it would be better to start again from the beginning as a lot of what has gone on above is confusing?

To start I'd remove FS4 and measure the transformer voltage Tx6 to Tx7 but I'm sure it's OK.
Then Remove TR7, insert FS4 (Slo Blo) and check the voltage between ground and D7 cathode.

This may help us see what Randall is up against.

[Randall]

I removed FS4 to measure TX6 and TX7, and when I powered up something went Snap! Nothing touching the chassis, everything was the same as the last time it was powered up. I informed the customer of this, and he said stop. He has already paid more in repairs then he paid for the amp, so as much as he likes it, he's done. I think it may have been the charred section of the board again, in hindsight maybe I should have dealt with that first.

So that's all for me. Thank you guys for indulging this, and apologize if I made things confusing. I appreciate you.