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Date: Mon, 24 Feb 1997 18:30:18 -0500 (EST)
>         by (8.7.6/8.7.3/AOL-2.0.0)
>         id SAA15928;
>         Mon, 24 Feb 1997 18:17:23 -0500 (EST)
To: <>
>Date: Mon, 24 Feb 1997 18:17:23 -0500 (EST)
>Message-ID: <>
>Subject: Re: [AMPS] 3-500Z storage
>In a message dated 97-02-24 17:26:03 EST, you write:
><<  have a Drake L4B that has been in the closet (sitting up as normal) for
> over three years now and I just brought it out. I installed new 3-500z's in
> about 1989-90 and am worried about the potential for problems. I also
> replaced the diodes and filter capacitors about the same time as the tubes.
> My plan was to bring up the HV supply slowly on a variac to "reform" the
> capacitors and bring up the filaments to check the voltage on them. What
> steps should I take to check for a gassy tube? Non-destructive steps :-)
> If a tube is gassy, is there anything that can be done for them? ie:
> re-evacuating?
> Thanks,
> Bill N4ALG
>  >>
>The 3-500Z has a tunsten filament and grid wires. Tungsten is a hard metal
>and with the thickness of the material in the 3-500Z it does NOT normally
>take a set from gravity. The tubes can be stored in ANY position, but should
>be operated vertically. 
>3-500Z's often gas up when left unused for a long time. The gettering agent
>is the gray coating on the anode (zirconium), and it is FULLY activated when
>the anode reaches a temperature of about 1000 degrees C. The anode is
>tantalum and molybdenum.
>The filament runs at 1500 degrees C, but it is too far from the anode to
>the getter. The only way to de-gass a 3-500Z is to operate it with some anode
>color. If you run metal anode 3-500's with no color, they won't degass.
>Tubes like 3-500Z can be gettered by running low HV, full cooling, and enough
>positive grid bias (negative filament bias) to turn the tube on at low
>voltage (do not exceed dissipation limits for the elements).
>73 Tom
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