Jon Elson writes:

Samuel M. Goldwasser wrote:


This ia an SP-120, probably from the 1970s. And, yes, those old tubes
do leak due to the Epoxy seals. Modern tubes do not leak.
I hate to dispute a known expert in the field, but as you say
this laser may be almost FORTY years old! Yes, the crummy old tubes with
sloppy epoxy seals may have leaked down in a few years, but even the
best HeNe all-glass tubes will eventually lose their He. It diffuses
right through the glass. And, the partially aluminum tubes
leaked much faster, still.

Not on any time scale that matters. New/MOS HeNes from the early '80s
with hard seals and even before when hard-seals were first introduced will
still work like new. So, yes, everything leaks eventually but they have
pretty much nailed the He diffusion through glass thing. That's not to
say every tube will be like that but it is more common than not.

--
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