Might it be worth just swapping the two tubes side for side? If this
phenomenon stays with the tube socket rather than the tube, could be it is
a matter of unequal filament supply. I had something similar in my SB-220
and swapping the filament contact springs cured it.
73, Pete N4ZR
At 09:00 AM 5/9/2008, jeremy-ca wrote:
>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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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
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