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Vintage threads from the first ten years

3/29/2002 9:00 PM
woodyc	Rc and RCA Here's a good one from RC-30: "The use of a cathode resistor to obtain bias voltage is not recommended for amplifiers in which there is appreciable shift of electrode currents with the application of a signal." This is true with AB biased 6V6 or EL84 tubes as soon as any signal is present, and it naturally gets more severe after cutoff. I'm beginning to wonder if those guys had any appreciation for good tone! By the way, I've been fooling more with Rc in my "5E3" and have come to the opinion that its best to use the smallest value I can get away with. For me at B+ of 365V its 240 ohms, which puts the black plates I have at 12.1 watts dissipation and other tubes like EH at 13.5 watts. I've found that smaller Rc values don't change the tone and they increase the output a little. For instance in my amp there is a 30% difference in power between 290 ohms and 240 ohms with no appreciable difference in tone. I haven't gone any smaller than 240 ohms. If anybody else has, I'd be interested in how it turned out. I have gone higher. At some point over 300 ohms you do start to get a noticable fuzz tone effect along with the power loss. I think the distortion is entirely due to the bigger cathode resistor. But there could be some contribution from having a larger signal in the splitter and other stuff like that.

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