ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
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
Dutch
email
Re: Xover dist. in dimed cathode bias amps
quote:
"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."
 
 
Chuck--  
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....  
 
HTH!  
 
C ya,  
Dutch  
 
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....

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