Thats perfectly normal for the glowing distribution. In fact Im looking at
one right now in a LK-450NT I just rebuilt and added 10M.
Carl
KM1H
----- Original Message -----
From: "bob" <n612dw@gmail.com>
To: <amps@contesting.com>
Sent: Monday, June 04, 2012 6:59 PM
Subject: [Amps] 3-500ZG are a glowing... but...
> Found a gem - brand new in the box B&W 2500A one of the last ones built,
> power cord was never attached and sealed manuals in factory bag with
> receipts. Owner apparently had a stroke as it was in shipment, been in
> storage since. Couldn't pass up the deal from the estate.
>
>
>
> Slowly re-formed (American made) caps and replaced bleeders with metal
> oxides at 3x the value - didn't want to burn 50 watts in the chassis for
> the
> originals. All is well.
>
>
>
> It has "new" 3-500ZG's from RFP. They seem to have very good gain, low
> grid
> current at rated output on my amp (PT-2500A, pair of 3-500s). About 1300
> watts out with ~65 in, over 1500 with 95 in.
>
>
>
> I am rather familiar with the Eimac 3-500Z's with the standard anode, but
> have never seen these ZG Frankenstein laboratory anodes before under load
> and lit up.
>
>
>
> Here is the thing. the std Z's normally start glowing rather symmetrically
> all around and vertically (not perfectly but.. ) and these ZG's seem to
> start glowing from the bottom of the tube up. They also seem to start
> glowing more slowly, as if they have much more mass.
>
>
>
> What I mean is, when the bottom 3 "biscuits" of the anode are orange, the
> top "biscuit" is still dark without color. Very uneven thermal
> distribution. Is this normal for these suckers or do I have an issue
> with
> the tubes. Or just run'em until I smoke 'em?
>
>
>
> Another detail - while new tubes never plugged in, they have been in the
> box
> since '96. I "re-generated" them on low anode voltage and de-tuned the
> amp
> to provide maximal dissipation in the tubes to allow the "gettering" anode
> to do its thing while glowing a dull red at the lowest power level. Did
> this for about an hour after running the filaments alone w/o plate voltage
> for about an hour (probably didn't do anything, but it couldn't hurt and I
> wasn't in a hurry).
>
>
>
> Ya gotta love the feedback from glowing tubes - makes the 87A rather
> boring
> by comparison. and that instant on too!!
>
>
>
>
>
> -bob, w9zv
>
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