alter 436c trouble shooting

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Nashanalog

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Aug 13, 2018
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8
I have been working on an alter 436c. pretty much a total rebuild. replaced the transformers with new sowter transformers, re capped it, and used diodes in favor of the old rectifier. checking voltages this morning everything looked pretty good except the voltage to the plates of the 6BC8 tube. instead of being 65v, as stated on the schematic it was at 315V!!!!!
now I know the voltages should be a little higher because this was originally built for 117v, but this is way off!
any thoughts and help would be much appreciated.

thank you
John
 

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Hey I rechecked the connections and it seems to be all fine. Still getting about 280v, which is considerably less than before, but it the schematic does say with no signal passing it should be around 60v and at 20db of compression it would be around the 280 reading.  :'(
 
Nashanalog said:
Hey I rechecked the connections and it seems to be all fine. Still getting about 280v, which is considerably less than before, but it the schematic does say with no signal passing it should be around 60v and at 20db of compression it would be around the 280 reading.  :'(

If it were all fine the voltages would be right.  I would check again until you find the issue.    Use your meter on continuity to verify connections from component leg to component leg, don't rely on visual verification.
 
I re checked all the connections with a multimeter. There was one cold joint so I fixed that. Now that the solder joint is repaired the tube is lighting up.... progress, but I am still getting the high voltage
 
I also measure the caps and resistors again, just to make sure everything was okay there, and those all check out. 
 
I check all the connections again, and they are fine. Is it possible I have a bad tube. I can’t think of what Else it would be.
 
Sound to me like the tube isn't turning on hard enough. You didn't answer about the components that scratched out. It looks like they would have an effect on the tube bias.
 

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