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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?
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Post by zpilot on Nov 20, 2017 14:31:36 GMT -7
I think what they are meaning is cathode bias, which of course is self-adjusting, even though it uses a "fixed" resistor. It's just a difference of terminology.
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Post by purpletele on Nov 20, 2017 15:40:05 GMT -7
Fixed Cathode means that there is an adjustable bias circuit to adjust the Voltage feeding the power tubes measured in mV
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Post by tonezone66 on Nov 21, 2017 9:06:46 GMT -7
Cheers guys! What does that technical solution mean, imply tonally speaking, compared to traditional fixed bias amp? Or vs. normal cathode bias amp?
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Post by purpletele on Nov 23, 2017 21:54:49 GMT -7
Cheers guys! What does that technical solution mean, imply tonally speaking, compared to traditional fixed bias amp? Or vs. normal cathode bias amp? For me and my limited experience I couldn't play a particular amp and tell if it was fixed or Cathode based. Maybe others can fell that difference and prefer one over the other, but that is cork sniffer territory for me.
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Post by Deleted on Nov 23, 2017 23:11:02 GMT -7
I tend to perceive cathode biased amps as a little more forgiving, compressed and softer in their attack. Fixed biased tends to be stiffer, open and more direct or forward sounding.
I tend to prefer cathode biased amps. They're like a comfy, warm blanket for us mere mortals...
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Post by zpilot on Nov 24, 2017 8:55:03 GMT -7
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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