At 04:54 PM 11/10/00 -0500, Chuck Counselman wrote:
...
>This is as much a question as an answer, but FWIW:
>
>I know nothing about 3-500Z's, but a close friend and co-worker
>successfully degassed quite a few 50-year-old (WW II vintage) 807's and
>other relatively small tubes by letting them run with (controlled) plate
>current. First he ran them with just their cathodes heated; but nothing
>happened. Then he applied B+ (a few hundred volts) and adjusted the grid
>bias to set the plate power dissipation to a healthy but safe level -- and
>the tubes degassed themselves within a day or two IIRC. Whether this
>technique will work with a 3-500Z, I don't know. Perhaps in an 807 the
>gettering material is applied to the plate, so it works when the plate is
>hot. I have no idea how a 3-500Z is gettered. Is its plate metal? Is the
>outside of the plate gray? If so, that might be a getter.
It's been recently said on this reflector (and not contradicted, which may
be almost a first!), that the gettering material in 3-500s is on the plate,
and that the plate must show slight color for the gettering process to
work. If these tubes are severely gassy, it could be a delicate process of
ramping up the plate voltage, adjusting the bias for just a bit of color,
waiting a while, ramping up a little more, and so on. surely adding a
glitch resistor in series with the +B would be a good idea regardless, to
limit current through any arc that occurs.
73, Pete Smith N4ZR
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