[Amps] Cracked Chimney

[Fuqua, Bill L]

 Many large tube amplifiers are operated without Chimneys. 
The most important thing is to make sure you have enought air flow across the tube
seals at the base and plate terminal. Most of the heat radiation goes thur the glass and
does not heat it up enough to be a problem. The chimeny does cool the glass some but it also
directs air to  the heat sink on the plate terminal. It is odd that the fins on the plate are in the 
wrong direction for this. 
   Some amplifiers have air blown thru the base to cool the  filament and grid seals and either
another fan to blow air to the plate shield and some to the glass envelope or a pipe from the
chassis to tansport some of the pressurized air to the plate shield. I have even seen one that
the pipe was made of a ceramic material and also served as a form for the plate RF choke. It also had
a right angle piece on the top to direct air to the plate cap.

73
Bill wa4lav

________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of Wayne Rogers [n1wr at chesapeake.net]
Sent: Friday, December 24, 2010 9:27 AM
To: amps at contesting.com
Subject: [Amps] Cracked Chimney

I have managed to put a crack in my chimney (SK-506 for 4-1000 etc).  The
crack is such that I am afraid that even the pressure from the metal clips
will cause a large piece of the glass to break off.

Has anyone had any luck either repairing such a crack or having a glass
repair firm do it?  I have looked around for some such repair service, but
have not had any luck.  I was hoping to find someone that repairs antique
glass.  I would think that in the right hands the glass could be heated and
re-joined?

As these chimneys are getting scarce I'd like to repair this one - but I'm
probably looking at a cost equal or greater than what I can pay for a
replacement.  Any thoughts?

Merry Christmas to all.
Wayne N1WR

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