Sunn 300T Bias circuit question/issue

[hiegdk]

Yeah, I'm worried there could be an issue with the board itself somewhere. I'm honestly tempted to ditch the board and use the iron and chassis to build something else.

[mresistor]

It's understandable given that a matched sextet of 6550 tubes is a considerable investment. I wonder what the output transformer impedance is and what else it could be used for? Do you have something in mind?

[hiegdk]

Don't have anything in mind other than keeping the basic topology of the output section sort of similar, ie: 6x 6550s, and voicing it for bass.

[tubeswell]

Did you observe the correct polarity when you replaced those caps? (For e.g., C162 needs to be in negative polarity)

[hiegdk]

Did you observe the correct polarity when you replaced those caps? (For e.g., C162 needs to be in negative polarity)

Yep! I was pretty careful about that. There's signs of scorching on the board in a couple of places and Fender boards from that era (and onwards) don't have a great reputation. I'm going to gut this thing. Gonna start another thread about ideas for a fun rebuild.