EL84s are a very common tube in such designs, 6V6s are, too. Thus, no biasing is required when replacing tubes - but using a matched set of replacement output tubes is, once again, highly recommended for obvious tonal reasons.Īmps with cathode-biased power-tube circuits are lower-output ones - 30 watts or less. Heck, even I could understand it without too much brain ache.Ĭathode bias is often referred to as “self-biasing,” as the design ensures that the tubes - wait for it - bias themselves. Of all the ones I researched, this was, by far, the most “guitarist-friendly,” IMHO. Basically, the tubes can’t tell the difference between having the grid negative with respect to the cathode or the cathode positive with respect to the grids, so either way can be used to bias an amp, however they do sound much different.” This creates a slight positive charge on the cathodes. In a cathode-biased amp, the grids are grounded through a grid return resistor and a resistor is placed between the cathodes and ground. In a fixed bias amp, a constant negative voltage is injected to the grids of the output tubes while the cathode is grounded to the chassis. “There are two common ways of biasing the output tubes - either fixed-bias or cathode-bias. In order to explain it both clearly and succinctly, I’m going to pull a quote directly from Gerald Weber’s wonderful tome, Tube Amp Talk for the Guitarist and Tech. This type of bias circuit is a little different than the one we’ve just been discussing.
Self bias takes care of tube drift? Please explain how it does that continoulsy?
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