Just to add a little more to this, I had six chimneys for the 4-1000 made
here last year by a glass blower at a university. After examining the
original chimney he told me it was Pyrex and went on to tell me more than I
can remember about why Eimac would have chosen Pyrex over soft glass for
this application. Heat and expansion coefficients were two things but
there was more to it than that.
If a few of you need chimneys and get together on it, you can go to a glass
blower and get the best price per chimney by getting him to make as many
chimneys as he can get out of a Pyrex tube. They buy these in 4 foot
lengths. If he has to buy the tube just for you, and you only want one or
two chimneys, the cost per chimney obviously rises. In my case, 6 inch
Pyrex tube (for the 4-1000 chimney) wasn't a stock item in his lab, so he
had to order one for the job. I told him to make as many chimneys as he
could get out of the tube.
Be careful with the glass blower you choose. Blowers that work with soft
glass (neon sign tube, decorative items, jars, etc) are out there by the
hundreds. But if they only have experience with soft glass, they likely
won't be able to do much with Pyrex. Find a blower that works with quartz
glass or Pyrex. I wouldn't have known that there would be any difference
until my experience last year with the chimney's. Its akin to assuming
that everyone that works in the "electronics field" is capable of easily
fixing a color TV and designing a pulse radar (they're both electronics
aren't they ?). Its sasme for glass blowers...and every other field of
endevour in the world.
Phil
At 12:35 AM 3/4/99 EST, you wrote:
>
>
>Hello again,
>
>> (friend is actually Jim, WF6R in Concord, CA)
>>Hello there, A good friend (wf6f) used cut cranberry juice jars for
>>4-400 chimneys with great success. I've also done the same with glass
>>apple juice jars and a cutter to remove the ends. Just keep enough air
>moving.
>>73's
>>skipp
>
>:And Carl added...
>:I tried that with 4-400's on 6M and 4-1000's on HF 30 yrs ago. Wound up
>with crazed :and brittle glass. Was also pushing the tubes to the limits!
>Soft bottle glass and :lantern glass does not have the additive compound
>:to efficiently pass RF. However when run conservatively I understand
>they can work. :OTOH, why run chimneys on a 4-400? Johnson sockets, some
>metal trimming of :the tube base and a SB-220 style fan will work for
>many applications.
>:73 Carl KM1H
>
>Hi Carl (and others),
>
>I realize a lot of this sounds silly, but I brought the topic of Glass
>Melting Temps up with the professional Glass Blower where I work. This
>was a short time ago when I approached him about repairing vacuum
>variables and chimney repairs.
>
>To sum up his information, he told me not to get too excited about the
>different glass melting temps and that mixed glass and quartz glass was
>better, but not by a great deal. I'll have to ask him more about the
>pyrex types of glass in the next day or so.
>
>I take this to mean that once your past a certain quality of glass, your
>pretty much in a safe zone for most of the normal applications. The Apple
>Juice Jars I mentioned are real thick.
>
>I much prefer the SB-220 method. If any of you have specific questions
>for my friend, I'll be happy to ask with a short delay time. He's a
>retired professional glass blower hired back when we couldn't find anyone
>else that had the skills.
>
>He has a very nice working shop... I'm still looking for a dead vacuum
>variable to practice on...
>
>73's
>skipp
>
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