Bill and Carl's sugestions are excellent . One more possibility is that one of
the sockets isn't making good contact so that tube is emission starved. Have
you tried swapping the 2 tubes in their sockets to see if the problem moves
with the tubes? Are the date codes on the glass similar? Check socket soldering
too..
73
John K5PRO
> In an L-4B amp I have just purchased, the two 3-500Zs show uneven plate
> glow at idle. Both tubes are Eimac 3-500Zs. Resting plate current is
> approx 180 ma for the pair, but one tube shows almost no color, the
> other quite a bit of color. Does this indicate overall condition of the
> tubes? At 100 watts of drive, I'm seeing about 200 ma of grid current,
> 650 ma of plate current at 2500VDC, and about 1000 watts output. I would
> think that a matched pair (which these probably are not) would show
> about the same amount of color, but this seems to indicate that one tube
> is drawing more current at idle, and probably more current at full
> power. I have not tried them individually. Any ideas or comment? Thanks,
> Charles, K4ZRJ
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