Post by nuclearfishin on Nov 28, 2010 10:51:37 GMT -7
I have a new EZG-50 which I think is really phenominal--way better than some of my original early BF amps. Anyhow, I'm going to swap out some tubes and was wondering if the amp needs to be biased, or can I just swap out the tubes and I'm good to go? I'm only trying out different brands, not trying to do any tube substitution or anything like that. Can I just swap away or are there bias adjustmants/values I need to watch out for?
You are definately going to have to rebias the amp if you keep the new tubes in. A quick swap out shouldn't matter as long as you go back to the old tubes but if you end up keeping the new tubes in then the amp will need to be biased again.
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I'd say it's always better to bias (or check the bias if nothing else) but it's not a must. Plenty of amps have no bias adjustment, and simultaneously are set to bias pretty 'cool' for most or all compatible tubes. And I prefer a colder bias tonally, myself.
Anyhow, I don't know how Doc sets the bias on these amps or the specs of plate voltage etc, but unless he's running a really hot bias (unlikely, from a tonal or a production standpoint), it's probably safe enough to plug in a well-matched set of tubes. And if you know the specs doc uses (like GT 6L6GC's #5 or something) than you can plug and play without a hiccup all else being equal. Worst case, if the bias is set hot or the tubes inherently pull unusually high current, The only thing you can damage is the tubes life and your tone - and nothing else, as Doc overbuilds everything.
Keep your eyes on any tubes and your ears open for any big loud hum, to make sure the tubes don't 'redplate.' If you don't get any redplating (and turn it off ASAP if you do) you're 'safe.'
However, the optimal, is as kfkm said, re-biasing to that particular set of tubes to a bias point you want, that is within reason; or bias to a ma current rating specified by the Doc, specific for this particular amp, it's plate voltage, and tube type.