[Collins] 32S-1 PLATE CURRENT

[Glen Zook]

Exactly!  All tubes do change as they age.
Fortunately, most of them do not change enough to
really alter the neutralization.  However, it has been
my experience with the 6146 family that the 6146B is
more prone to these changes with age, especially
during the first several hours of operation.  That is
why I caution people who are using the 6146B in place
of the 6146 / 6146A to watch the neutralization
especially in the first few days after installation if
the 6146B worked in the first place.  Frankly, most of
these changes will occur within two or three hours of
"hard" operation.  But, very few amateurs actually
operate their equipment that long at a time.

The ratings of both the "normal" 6146 / 6146A / 8298
and the 6146B / 8298A series of tubes are lower for AM
operation than many people run in their transmitters. 
Thus, the life expectancy of their final amplifier
tubes is only a fraction of what it is when the tubes
are run properly.  The difference between 180 watts
input and 150 watts input with the resulting 15 watts,
or so, output difference, doesn't make a "hill of
beans" worth of difference at the other end, but it
sure makes a difference in tube life.  However, that
is still outside of the actual AM ratings of the
6146/6146A series.  By dropping the input power to
around 135 watts, the tube life can often be 10 times
(or even more) greater than with running over 150
watts.

The 6146B series is, in my experience, harder to
"tame" than the 6146/6146A.  I have had considerable
experience with the various 6146 versions at VHF
including thousands of Motorola commercial FM units. 
You definitely do not want to replace the
6883/6883A/8032 (12 volt filament equivalents of the
6146/6146A/8298) with the 6883B/8032A/8552.  I tell
what happens when that is done in the article that was
in Electric Radio.

When RCA first announced the 6146B/8298A in mid-1964
they advertised that all you had to do was to plug the
new tube in and run 33% more power.  Well, it didn't
turn out that way!  In my opinion, it was not a good
idea to have used the 6146B nomenclature for that tube
because it really is different from the 6146/6146A. 
Of course, the only real difference between the 6146
and the 6146A is that the 6146A has what RCA called
the "dark heater".  Supposedly the "dark heater"
worked better under varying filament voltage
conditions and was more "rugged".  You can mix a 6146
with a 6146A.  But, NEVER mix a 6146B with either of
the older versions!  That will get you in trouble
"real fast"!

I know people who have used 6146B tubes in place of
the earlier models without a single problem.  I also
know of a lot more people who have tried to use the
6146B series that have had problems!  I have found an
occasional transmitter that is very happy with the
6146B.  But, the vast majority of transmitters that I
have seen (and I have seen a lot over the years!)
really don't like the 6146B.

Thus, I advise people to be careful when they replace
the 6146/6146A with the 6146B in transmitters that
were not designed for the 6146B.

Glen, K9STH



--- "Dr. Gerald N. Johnson, electrical engineer"
<geraldj@isunet.net> wrote:

When the neutralization changes, then either the tubes
or those potentially temperature sensitive parts are
changing and probably should be replaced.


=====
Glen, K9STH

Web sites

http://home.attbi.com/~k9sth
http://home.attbi.com/~zcomco

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