>I've just acquired an SB-220. The amp has most of the standard
>modifications -- but the 3-500s have not been in service for some time.
>While the tubes are known to be good, I'm curious what you think might be
>the best way to rejuvenate these glass power tubes?
Large thoriated-tungsten filament Ceramic tubes can be restored to full
emission by re-carburizing the hot filament with acetylene gas (C^2 H^2).
The two carbon atoms in the acetylene molecule combine with tungsten
atoms in the filament to form a thin layer of tungsten di-carbide -- the
depletable/renewable compound which is responsible for c. 99.5% of
electron emission. The remaining two atoms of hydrogen are evacuated.
Glass tubes (the 8166 / 4-1000A) have been recarburized, but the cost was
found to prohibitive.
- If one of your tubes has a seal leak, it will exhibit blue light on
standby. Some amplifier experts preach that a gassy tube will get better
by itself, but it just might be better to get on the phone and order a
new 3-500Z, since I have never seen a gassy tube rid itself of gas. The
Chinese 3-500Zs currently sold by RF-parts seem to be bias-compatible
with the old Eimac 3-500Zs (Mu=130). A caveat-- Triton 3-500Zs have had
a problem with defective anode cooler welds.
>
cheerz, Paul
>StoneyGround Station
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- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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