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previous: Mark Black Have you replaced those bias filter... -- 1123919294 View Thread

Re: hot tubes, I mean really hot

8/13/2005 8:44 PM
pete
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Re: hot tubes, I mean really hot
Yeah I swapped the electrolytics, and checked out the bias circuit, which looks good. I found a bunch of discrepencies in the layout from the schem. So I changed all of those (I hope). I took the following voltages:  
 
from cathodes of the rectifier I get 114V  
from the anodes I get -66.5  
from the other side of the 15k and second electrolytic, I get -31.4  
(all referenced to ground)  
 
I tried this with a zener regulator and without, and still the same problem. My cirucit is a little different than the original jcm 800. From the 300-0-300 I utilize both windings which go to 100k resistors and then each one of those to the cathode of a 1n4007. Anodes are tied together and then go to the cathode of the first electrolytic bias cap and a 15k resistor. On the other end of the resistor is the secnd bias cap (10 &mu amps) and formerly a zener diode was in parallel with this cap (cathode of zener and anode of cap to ground). The other side on the cathode of the cap then goes to one of four bias pots. Hope this doesnt confuse too much.  
 
Right so, I have rebuit the circuit a few times changed all resistors, all diodes. All fuses are in place and not blown. My next step is to replace non-electolytic caps further on in the bias circuit. Thats the only other thing that I can think of.  
 
Thanks for your help.  
Pete

 
Replies:
Mark Black Seems like you're getting a lot of ... -- 8/14/2005 2:23 AM