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Re: hot tubes, I mean really hot

8/14/2005 2:23 AM
Mark Black
Re: hot tubes, I mean really hot
Seems like you're getting a lot of drop across that 15K resistor.  
Wait a minute! I just re-read your post more carefully and noticed the mention of four separate bias pots. If those pots are used as voltage dividers with all tied to gound on one end and the 15K/Cap node on the other they would be effectively in parallel. And if they happen to be 50K pots the total load on that part of the circuit is around 12.5K which as it happens would yield (according to the math) almost exactly the -31.4V you are measuring.  
You might need to go to 250K pots for the bias trims, or maybe better yet 100K pots run through 220K resistors to ground, which should give you approximately -38V to -56V range of adjustment for each tube, although my experience in the real world tells me you might have to fudge the values a bit for best results.  
Am I on to something?  

pete Mark! That was it. I get -62V at ... -- 8/14/2005 7:26 PM