[ARC5] BC-453 B dynamotor hum

[J Mcvey]

I probably should have posted the 600 m event since everybody here has a beacon receiver! 

Now back to that pesky hum:I think there is something going on with the 12A6. The rig is nice and quiet at zero gain when it starts up cold or even luke warm. one it gets hot there is an intermittent hum, then eventually a steady loud hum.  I monitored the grid and the cathode of the tube. I found that as it heated up the cathode bias went from almost 14V down to about 12V in full hum mode.The overall supply starts out at 205V , then ends up at about 186 when its humming.  the only thing that can draw down the supply like that would be the 12A6 . The 200 HZ does t appear at the grid, but no DC.  Tried shorting the the detector to ground with a large cap, but the hum was unaffected. I disconnected c30 and subbed another cap, but no joy. 


I'm thinking that it might be a bad tube with some kind of internal short or gas or ????
 


     On Saturday, October 31, 2015 8:57 PM, David Stinson <arc5 at ix.netcom.com> wrote:
   

 
> Been tweaking this beacon receiver in preparation for the 600m 
> event in November.

What 600 Meter event? 

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