Q: Value of bias feed resistors in 1983 JCM 800.

[Humbucker]

I was reading an article just recently by the late/great Ken Fischer and he said that when it comes to Marshall amps with EL34s, it's a good idea to change the stock 220K "bias feed" resistors to something lower like 100K. This apparently helps prevent EL34s from wearing out prematurely.

I had also read this same advice in Kevin O'Connors' TUT1 book.

I just bought myself a 1983 Marshall JCM 800 2204 last week and had a look inside the chassis, it turns out that my amp does have these two 220K bias feed resistors. Should I replace those with a pair of 100K resistors the next time I go and retube the amp? Or will something like JJ Tubes be fine with these stock 220K bias feed resistors?

[J Martin]

Resistors are dirt cheap. Select a few values between 220K and 100K and see if you hear a difference. If you don't detect any audible changes then go with what Ken and Kevin deem "safe". I don't own a Marshall at the moment, but I sure service a lot of them. This might be a good thing to add to the knowlege base.