On Tue, 25 Nov 1997 07:31:22 +0200 gsmith.rdi@reutech.co.za (Greg Smith)
writes:
>Hope this is not too late to be out of context, but our server has
>been
>giving trouble for a couple of weeks, and I only read the interaction
>about
>3-500's this morning.
>
>I was off the air for abt 4 years, and my 3-500's were in storage. I
>can't
>remember which way up they were.
>
>On trying to fire up my linear again, they appeared to have gassed,
>causing
>severe fireworks. I have managed to partially recover them by placing
>high
>value resistors in series with the plates and allowing them to soak.
>The
>getter then seemed to soak up enough of the stray air to allow me to
>apply
>HT without the resistors in series. In fact the standing current is
>back
>to normal, and I can generate abt 70% of the power I used to get.
>
>They seem to run much hotter than before though, in spite of the fact
>that
>I have doubled up on the fans, and again start to glow blue if I allow
>them
>to get too hot. (I've run a pretty exhaustive check for parasitics)
>
>(Some of you may have noticed that I use a lot of pauses while CQ'ing,
>and
>that's the reason).
>
>I would be surprised if this has anything to do with the orientation
>in
>which I stored the tubes, but someone may like to put me right on
>that.
>
>Any comments?
>
>Greg, ZS5K
Sorry about that mis-posted message Greg.
The 3-500Z requires the plate to show lots of color in order to outgas
properly.
I suggest increasing the idle current to near the rated dissapation and
let them cook for 10 minutes at a time; then retest. Do not drive with RF
and be certain you have plenty of air.
You can substitute a string of reverse connected 1N4xxx or 1N54xx diodes
for the bias zener for this test.
If the PS is not up to it, try 1 tube...unless it is a TL-922; then you
have to get creative.
GL Carl KM1H
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