Marshall plexi no bias voltage

[Vpvalmus]

I just recently purchased this 1968 50 watt. When I got it, the bias has high with not trim adjustment. So, I check the bias caps and one was total dead. So, I replaced the bias caps with 8uf 150v, I also lifted the ground on the filter caps to tested them, and they were within specs. I changed out the ohm selector with a period correct one. I was using the bias master to check the bias. Now, there is 0 bias voltage and about 490 B+ voltage. Any ideas? Thanks

 

[Vpvalmus]

I got a message that the bias resistor may be the issue and it was a cold solder joint. Thanks,

 

[Pete Farrington]

check the bias caps and one was total dead.

What do you mean by 'dead'? eg short circuit, open circuit ...

filter caps to tested them, and they were within specs

What specifications were you using, which did you test?
With an unknown amp, it's good practice to verify adequate bias voltage before fitting the valves.

 

[Chris-in-LA]

I got a message that the bias resistor may be the issue and it was a cold solder joint. Thanks,

So, it’s all better now?

 

[Marcomel79]

Install a trimpot while youre there