previous: John Dan torres says the plate load resi... -- 3/1/2000 12:04 AM

Re: Varible 12ax7 cathode resistor in preamp?

3/1/2000 2:10 AM

Gil Ayan

Re: Varible 12ax7 cathode resistor in preamp? quote: "Dan torres says the plate load resistors have to be consistent with the cathode resistors.That is,if you change the cathode resistor,you have to change the plate resistor.What the hell is he talking about?   "     I can see a plate load resistor getting damaged if the tube shorts, because there is a significant amount of power being dissipated... say you have 250VDC on the plate, is the tube shorted, say you're using a 100K plate res, you'd be eating V^2/R = 250 * 250/100,000 = .6W, so you would damage a 1/2 watter resistor (so, use a 1W there!).     But, in the same tube (well, short) the current would be approximately V/R = 250/100,000 = 2.5mA... and the 1.5K resistor would dissipate I^2 * R (assuming a 1.5K) = 2.5 * 2.5 * 1.5 *1000/(1000^2) = .01W... THere is no way that resistor would be stressed at all.     In other words, I don't know what Torres is talking about -- some might like to re-phrase that to read, "I don't think Dan knows what he's talking about!"     Gil

 

Replies:

Richie I think if you look at the chart -- 3/1/2000 5:51 AM