----- Original Message -----
From: "Robert Mccormack" <zl1aih@xtra.co.nz>
To: <amps@contesting.com>
Sent: Sunday, December 26, 2010 2:18 AM
Subject: Re: [Amps] Cracked Chimney
For those on the list that have them, see Bill Orr's "The Radio Handbook"
14th edition, pages 580 through 583 - 'A 4-1000 Pi-Network Amplifier'. (I'll
bet Carl has one)
** I have that HB as well as Edition 15 which is the one that has a pair of
them and got the ARRL screaming to the FCC. It was gone by the next edition.
There are a couple of 4x1's sitting around here waiting for a project, most
likely as modulators for a pair of 6C21's or something bigger.
The glass chimney is not specified and neither is the socket - just a
"special air socket".
Note the concave top directing forced air cooling across the anode
connector.
Mid-1980s I needed a Coleman lantern chimney and found a replacement in a
small hardware store. The owner offered me his entire obsolete stock of
Coleman chimneys (all 4 of them) for NZ$10. The largest one was identical to
the one used in Bill Orr's amp.
(I gave it to a friend for his 4-1000 amp project.)
If I needed that 'Pyrex' chimney now, I would look for those big Coleman
lanterns in small-town antique stores before the owners realise that the
chimney is worth more than the lantern.<G>
** The metal chimney was used in shake tables, for obvious reasons, and
probably many other non RF applications.
Im surprised the 4x1's survived no matter how well the shock mounts were.
You could feel the vibrations in the wooden floors of the old mill buildings
that housed many electronics defense contractors in New England. I used to
regularly get pulls from National and Sanders Associates when I worked there
as well as local BCB stations. Ive lost track of how many one and two 4x1
amps Ive built for others over almost a 30 year time.
Carl
KM1H
73, Ken ZL1AIH
None these make a really good replacement for a glass chimney for what
should be obvious reasons. The glass transmits radiant energy freely.
Silicone rubber and fiberglass both absorb this energy almost as
readily. That means they need a wider spacing from the tube envelope and
more air to keep the new chimney cool. How well the forced air cools
the chimney remains to be seen, but fiberglass, silastic rubber (TM) and
even ceramic used on a glass tube is an entirely different proposition
compared to using them on external anode/metal tubes.
I think the earlier suggestion make by some one to use cut large glass
jars such as pickle jars is probably both the best and cheapest approach
although it does take a bit of practice to make a good one. Done with
care you can get the straight sides and slight curve in at the top to
cool the anode seal..
73
Roger (K8RI)
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