Quote:
Originally Posted by miniman82
Looks like the vertical lin needed some tweaking, I suppose there's some more caps that need replacing in that circuit.
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The set has been fully recapped, but I used the cheap generic yellow caps. I wonder if one failed ?
Quote:
Originally Posted by Kevin Kuehn
It might be interesting to put the original caps back in the horizontal oscillator and output section. Sometimes I wonder if our modern caps don't shield these circuits properly from outside interference. One end of the old paper caps were marked with the outside foil shield. That end typically went towards the lower potential voltage source.
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I suppose I could dig them out of the trash. I've heard there are tricks for determining the outer layer in modern caps using an RF generator and oscilloscope. I think the idea is to put the probe tip against the body of the cap, apply RF to either end and observe the signal strength on the scope. The stronger end will be the outer layer.
Quote:
Originally Posted by Phil Nelson
I believe that I observed it in my Hallicrafters T-67:
The interference is seen as squiggly vertical lines running down through the reporter's face. It disappeared after I replaced the 6BG6T horizontal output tube, just as suggested in an old service book. The book noted that Barkhausen's is more prominent with weak signals than strong ones.
Another solution is to place a small circular magnet around the tube. The DuMont RA-103 has a little magnet mounted inside the HV cage to suppress Barkhausen's.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html |
I swapped out several 6BG6s and it had zero effect so I think the problem lies elsewhere. My suspicion is the mica cap inside the yoke across the horizontal windings. It's not so easy to get at though.