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previous: JCS Thanks for the reply Matt. Yes that... -- 4/7/2000 8:36 PM

Re: Plate voltage on BFD

4/7/2000 11:07 PM
Matt	Re: Plate voltage on BFD Now that makes sense. There are two schools of thought that are not mutually exclusive on biasing-by plate current or by dissipation. By plate current can be meaningless. As an extreme example, say a 6L6 is supposed to be biased at 35 mA. Well if this was done in a Musicman with up to 700V on the plates, that would be pretty hot. But in a Pro with 440 V, pretty cool. Plate dissipation in tube manuals is plate to cathode voltage times plate current. If you go the convenient route and measure cathode current, it will include essentially plate and screen current. Therefore, you can estimate screen current using some tube charts. So cathode current=plate current + screen current. Since you don't want to bias a tube too hot, it's better to underestimate screen current, imho. Also, as far as risk, the 439 V isn't particularly bad, but I was mentioning that the caps are potentially being hit hard. That's something everyone lives with. Check out the power supply design program at www.duncanamps.com for some cool simulations. Matt

4/7/2000 11:07 PM

Matt

Re: Plate voltage on BFD

Now that makes sense. There are two schools of thought that are not mutually exclusive on biasing-by plate current or by dissipation. By plate current can be meaningless. As an extreme example, say a 6L6 is supposed to be biased at 35 mA. Well if this was done in a Musicman with up to 700V on the plates, that would be pretty hot. But in a Pro with 440 V, pretty cool. Plate dissipation in tube manuals is plate to cathode voltage times plate current. If you go the convenient route and measure cathode current, it will include essentially plate and screen current. Therefore, you can estimate screen current using some tube charts. So cathode current=plate current + screen current. Since you don't want to bias a tube too hot, it's better to underestimate screen current, imho.

Also, as far as risk, the 439 V isn't particularly bad, but I was mentioning that the caps are potentially being hit hard. That's something everyone lives with. Check out the power supply design program at www.duncanamps.com for some cool simulations.

Matt