I have seen questions about low-cost chimneys on the
reflector from time to time and thought I would add a note
for what it's worth.
Pyrex glass chimneys for the 3-400, 3-500, and 4-400
family are relatively expensive from Eimac. It is pretty
well known that Coleman "double-mantle" gas lamps
use a chimney that will work with these tubes and they
are relatively widely available from stores that sell
camping equipment.
But there is a need for an inexpensive chimney for the
3-1000 and 4-1000 size of tubes. The Pyrex glass chimneys
from Eimac are even more expensive for these larger tubes.
If you are a "by-the-book" sorta guy please read no further--
I wouldn't want to offend you.
Needing a number of chimneys once for a group of single-band
contest amps using 4-1000s I looked around and discovered
that the 1-gallon, wide-mouth pickle jars are the right size.
There is a pickle packer nearby (Kuner's) and I bought a
dozen unused jars from them (4 to the case). New jars because
I couldn't wait long enough to eat that many pickles and I am too
frugal to bear the thought of dumping that many pickles
into the garbage.
These are the jars that have the wide mouth and the screw-on
lids. Yes, I knew they were not Pyrex glass but I needed
chimneys right away and decided to try them anyway.
(I now see a lot of pickles being packed into plastic jars--
but I would not recommend using them!)
I mounted a glass cutter in a bench vise about an inch
above the surface of a work bench and clamped the
vise down so it couldn't move. I then placed the jar on
the bench and rotated it ONCE around while scratching the
surface with the glass cutter. Then I took a length of
NICHROME WIRE and wrapped it once around the tube,
trying to keep it in the scratch I had just made with the
glass cutter. I overlapped the wires a bit to make contact
around the entire circumference of the tube--but
keeping the wires from touching at the crossover
point. A big Variac provided the power to get the wire
red hot. It only took a few seconds from the time of
applying the power to when the jar went "tink" and the
bottom popped off.
I also tried to remove the threaded portion of the neck
so that the chimney looked more like an Eimac one.
But I did not have as much luck doing this because the
"necked-down" portion was much thicker and varied
widely. Although I was able to pop off the threaded
portion of the jars--the cut was not always perfectly
smooth--like the bottom was.
So I decided to leave the threaded portion on the jar
and use them that way. It actually maintains the air
flow around the plate cap anyway--so it is probably
better, even if it is not as aesthetically appealing.
Now the question was "did the cheap glass chimneys
actually work?" And the answer is--YES! They worked
for many years, until the big amps were retired.
I am sure that Pyrex glass is better, but if you can
keep plenty of air flowing around the tubes, a chimney
made from surplus pickle jars will also work. And
it provides a use for your old parasitic-suppressor
nichrome wire that is no longer being used.
I am no "expert", but I am a trained professional--YMMV.
--John W0UN
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