[Amps] Uneven tube glow in pair of 3-500z

[Bill Fuqua]

     Examine the tubes closely.
The 3-500z's plate can sometimes be knocked off center slightly if dropped 
most likely in shipping.  It is more common in 3-1000Z  and 4-1000A tubes 
because they have more massive plates. An off center plate can cause more 
current to flow to one side of the plate than the other. If these are EIMAC 
tubes they have been around for some time since EIMAC quit making  some 
time ago.

73
Bill wa4lav




At 08:20 PM 5/8/2008 -0400, Charles Johnson wrote:
>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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