[AMRadio] WTB : PP 6F6 Output Transformer for BC779


Jim Candela jcandela at prodigy.net
Sun Jul 11 08:44:19 EDT 2004


Mark,
 
   I don't have a transformer but such a device should be readily available from multiple sources. Hammond transformers should have something. The trick will be to get something that looks like the original, or that might fit inside of the original case.
  You seem to suggest that the reason for the hot 6F6's is a bad output transformer. I don't have the schematic of a BC-779 handy, but in general I'd look at the dc operating point first. Maybe the bias is wrong, or the screen voltage is too high. A turn to turn short in the output transformer might cause the distortion, but it would not shift the dc operating point (no audio drive) to make hot-biscuit tubes. I recall an email thread here not long ago about hot 6V6 output tubes, and short tube life.
 
  Good luck in your restoration,
 
73 Jim Candela
WD5JKO

Mark Foltarz <Foltarz at rocketmail.com> wrote:
In the process of restoring a BC779, I replaced a bunch of caps and a several
resistors. I also noticed that there were two "tar stalagtites" forming
underneath the audio outout transformer.

Upon power up lo & behold, there was very little audio out and the 6F6's were
truly hot enough to fry eggs on.

I pulled the 6F6s and hooked a pair of headphones to the secondary of the audio
driver transformer and began listening to some SWBC with just a foot of wire on
the antenna.

So, anyone have a spare 6F6 PP to 8ohm to part with ?

tnx

de KA4JVY

Mark






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