Post by tonezone66 on Nov 20, 2017 14:00:00 GMT -7
Could someone tell me what exactly means the term "fixed cathode bias"? I do know the terms fixed bias & cathode bias but not the one I'm asking about. I've seen this term at least in the descriptions of Victoria amps, for example Victorilux.
And also how does a "fixed cathode bias" amp relate tonally to a normal fixed bias amp and to cathode bias amp?
Last Edit: Nov 20, 2017 14:00:40 GMT -7 by tonezone66
Out of curiosity I looked at the Victoria Amps website and I can't find where it says "fixed cathode bias" anywhere. As far as I know there are only 2 ways to bias a tube. Someone correct me on this if I'm wrong. One is cathode bias, which uses Ohm's Law to vary the bias of the tube at the cathode. The other is grid bias which uses a resistor, either fixed or variable, to set a voltage to the grid. This is usually called "fixed bias". That's it. That's all there is. I've seen a combination of these two used but it didn't work very well.
The Humbucker Music ad for the Victorilux doesn't use the term "fixed cathode bias" either but it does say that the amp was derived from a "AB765" circuit so that would be fixed bias. Also, the claimed wattage for that amp would require that type of bias.
So to answer your main question, I can't tell any difference in tone. Cathode biasing adds some compression so it behaves a little like an amp with a tube rectifier. That's one of the reasons I like my JAZ 20/40. It is less efficient than fixed (grid) bias so the wattage is a little less. That's why you didn't usually see it in higher powered amps.
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