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previous: Chuck Thanks Dutch,I figured it w... -- 1/8/2004 3:05 PM View Thread

Re: Xover dist. in dimed cathode bias amps

1/8/2004 5:28 PM
Re: Xover dist. in dimed cathode bias amps
"I'll probably run a signal through the amp and turn up until I get the audible Xover and target a tad below that voltage."
One thing to note is that the Zener voltage is not rock steady with changing current, but will vary a volt or two as the current goes up from zero.  
The 12V Zeners in my stereo amp end up at more like 13V each by the time the bias is dialed up to provide maximum idle plate current (around 220mA). This is still close enough to provide protection to my peramp tube filaments, which serve as the cathode resistor.  
That's why I suggested averaging the two voltages--below the Zener threshold, you get straight cathode-biased operation, and by the time the Zener stabilizes (i.e., draws enough current to turn all the way on), it'll end up being closer to the high end of the range, but likely still below the crossover distortion threshold....  
C ya,  
PS: while you're surfing my way, check out the adjustable cathode bias trick on my site as well. It lets you set your idle current with pretty much any bogey set of tubes to idle at the desired current....

Chuck Gotcha. I was wondering about how a... -- 1/9/2004 5:42 AM