Tubes sometimes age differently even when they start out in the same amp.
There is also slight differences in cooling flow.
You can test them individually and if one gives close to new output then buy
one new tube.
My tendency would be to run them as is until they drop down below 750-800W
and start over with a fresh pair.
Some have reported that running the filaments at around 7-8V for a half hour
will rejuevanate some tubes.
Carl
KM1H
----- Original Message -----
From: "Charles Johnson" <k4zrj@bellsouth.net>
To: <amps@contesting.com>
Sent: Thursday, May 08, 2008 8:20 PM
Subject: [Amps] Uneven tube glow in pair of 3-500z
> 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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