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Re: Ovens.
Yes, I see your questions.
1. For quite a while I used to use a thermocouple on my glass at one point to
measure the glass temperature, and would go up to at least 600 degrees F.
After a while, I got used to this and found that the flame is a bit more
reliable, and really gets it to an even better temperature. Remember, the
point is to get the glass as hot as it will go without actually softening it,
this is pretty close to the annealing temperature. The glassblowers all use
the sodium flame trick anyway to anneal the glass. After a while, it was
second nature to spread the flame around evenly, and the proof of being
finished was not seeing any further reaction to the heat on my vacuum gauge.
When I can go all over the glass and not cause any new bursts of gas seen on
the ion gauge, it's done. I just make sure to cover the whole thing. The ion
gauge becomes your sensor for the process. If you have unusually dirty glass
or a very humid day, the thing makes you go longer til you are finished. If
there's a leak, the thing tells you even if it's extremely small and
virtually undetectable by eye, such as a micro-defect in the electrode.
The point is that the gas is much cheaper than electricity and it's much
quicker than an oven. You don't have to wait for the mass of the oven to heat
up and cool down, just the glass, which only takes a minute. Ovens may be a
slight bit better quality wise but the difference is not worth the effort.
For crackle tubes, of course you need an oven, but that's a very special
case.
With this system, I have never had a tube that I could not bombard, and in
fact there are many tubes that are difficult to bombard electrically that I
can do with no problems, such as large tubes with sections close to the
transformer that pass close to one another (causing arc-over in bombarding),
tubes with parallel electrodes that almost touch one another (I use one large
coil to heat both electrodes at once in that case) and 6mm tubes with 7mm
electrodes.
Jeff Golin