Tube Biasing

[Salamander]

I finally wrote to the seller who sent back internal photos of the amp with arrow pointing to where the probe should be touched, the answer, pin 8 (thanks Jez) Starting again I've managed to set all four tubes at 0.38v, the seller quoted 0.4v but I dropped it a touch after reading advice on here and elsewhere. I will be checking again in 4 weeks to see if any of the valves are drifting, hopefully not, but I can confirm the amp is sounding good. Once again many thanks, and hopefully I will not have to ask again for more help.

 

[Salamander]

Well I'm back with one more question, I've been setting the tubes at 0.35v, one of the tubes has had to be set a little lower, the adjuster would not turn any further, now today when checking, two of the valves, 1 and 3 I've been able to set at 0.35v, tubes 2 and 4 only 0.23v, does this mean they are ready to replaced? If so, I've looked at replacing with 6550's, any comments welcome.