Bassman troble shoot Where would you begin?

[Markusv]

Folks. I'm looking for help please

A friend has a 59 Bassman clone (built by Sligo amps in the US)
The amp sounds great at low clean volumes.
As soon as one cranks it, there is a ratty distortion sound and the sound sort of cuts out.
This started suddenly leading me to believe it is component failure

Here is what I have done thus far:

Re-flowed all solder joints
Replaced the SS recifier diodes that are permanently wired onto the socket holding a Weber Copper Cap
Tested all speakers for continuity
Tightened all tube socket pins
Measured all components for value
Replaced the normal wire on V1 input with shielded in case there is blocking distortion
Checked the power cable
Checked the OT for continuity on both sides
Tested tubes by using a full new set

The problem persists.
I only have a DMM and no other sophisticated equipment
What else should I do?

Thanks

Markus V

[Prairie Dawg]

I would probably start by checking the bias current for the proper range. It sounds like crossover distortion,

[Lynxtrap]

How about oscillation, bad grounding or too little filtering?

[tubeswell]

And did you put a new set of 6L6s in to see if it was one of those? (e.g.: screen failure - causing lack of plate current in one side - can cause ratty distortion of the type you describe)

Otherwise have you VAC tested both sides of the OT primary? One side may be open?

[Markusv]

Hi Folks

All good suggestions
I will have a look later this weekend and report back

Thanks all!

Markus

[marshamps]

I recommend you call Steve Clark. He's a good guy and will will help get your issue sorted out.