[Collins] output tubes

[Dr. Gerald N. Johnson]

On Wed, 2008-07-09 at 11:04 -0400, yash at aol.com wrote:
> Moving along on my KWM-2A project,I started looking at the output 
> tubes . The rig has 6146B in it now. I went to several site and found 
> the
> 6146W was a good replacement. Then reading another site.the 6146 W was 
> a BAD choice. Got the same answer from several of the listed vendors 
> ,but no real facts.
>     Since I have to replace the existing outputs ,what version of the 
> 6146 SHOULD I be using. Iam confused with all the different answers so 
> I thought I would as here ,for the right one.
> thanks for the help
> dale wt4t

Its confusing. The major problem is that the early PA neutralization
circuit won't neutralize the 6146B or some 6146W. That's because the
6146B and those 6146W based on it have greater capacitance between the
electrodes than the original 6146. Those KWM-2 and S-line with an 8-50
ceramic trimmer in the neutralization circuit probably can't be properly
neutralized. Those with an air trimmer are designed to work with all
available 6146 versions. A possible problem with the 6146W is that some
were selected 6146 or 6146A and some were selected 6146B. I don't know
that its easy to tell which they are.

If they can be neutralized, I prefer the 6146B because it has greater
power capabilities and if run at 6146 ratings has the potential for a
much longer life. I don't like to see the output tank of the S-line and
KWM-2 abused by running the additional power the 6146B is capable of.
Some parts, particularly the compression mica loading padders, are very
hard to find as replacements.

To add to the confusion, I've been told by Warren Amfahr (W0WL) who
claims to have developed the PA circuit for Collins that the 6146 is not
as linear as the 6146A that he says was created by RCA for Collins to
use in linear amplifier stages. Unfortunately the Collins transmitter
manuals that I have never discriminated between the various 6146
versions in their parts lists and show the same part number from the
early 32S-1 that predates the KWM-2 through the latest manual for the
32S-3A. I've not found data sheets to corroborate that story either.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer