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Most valves are rated for 5000 hours use, although a guitar amp may well be regarded as abuse....
Not my intention and see no need for sarcasm? I am merely pointing out that I did not have any request for a hotter bias.
I do not promote the company and certainly have no financial interest. I post in two other forums ( HR and SoS) and mention the company very rarely unless I feel it is relevant. No one at those forums has ever given me the slightest indication that I am out of order.
I also do not run my own company making or repairing amplifiers.
Dave.
Be wary of any post that says the correct figure is 38 ma or whatever, they don't know what they're talking about, you need to measure the plate voltage as well, eg Marshalls are all over the shop. Meaning the required bias current will vary accordingly.
Like @martinw said, do the maths, it's a simple a X b = c thing. Oh yeah and adjust per @ICBM. And of course, Safety First in there. Get your head around it first before trying it.
Anyone who has ever monitored bias current over a few hours will see it vary by several mA up and down. Va will of course vary with mains voltage.
Quiescent Ia will depend upon the program history (the problem with many early hi fi transistor designs) . New valves will invariably have a high initial grid current which can vary by several 100% depending upon brand and quality (they don't "burn" them you know!) Running the bits off the OP stage for an hour will drop grid current by 2 or 3 times..THEN check bias.
Depending upon how negative bias volts are derived, tracking with mains voltage changes will be close or poor.
Dave.