> But of four spare unused 3-500z tubes, that were on the shelf
> for 12 years, only one has proved to be OK. The other 3
> are displaying internal shorts or gas leaks.
I had a chuckle at a hamfest.
A fellow was selling 3-400Z tubes, and I bought the used ones. My
friend bought the unused ones at twice the price.
All of them were several years old, the only difference was the
seller claimed mine had been used up to a weeks before.
My tubes worked, while the unused ones arced.
You can sometimes restore the tubes by running them at low
anode voltage (1000 volts or so) with POSITIVE grid bias (mindful
to not exceed grid dissipation ratings). Use a low resistance in
series with the anode in case the tubes fault.
Just bias the tubes up until the anodes show a tinge of red, and
cook them for several hours off and on for a week. (Don't try this
with Chinese tubes, they are built too poorly)
When my friend decided to toss his tubes out, he gave them to
me. I gettered them that way, and wound up using them for years.
73, Tom W8JI
w8ji@contesting.com
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