[Boatanchors] 6146 question

[Glen Zook]

Whether or not a 6146B / 8298A (or 6146W made after
1964) will work in a particular transmitter that was
designed for the 6146 / 6146A / 8298 is a "crap
shoot"!  Some rigs work fine with the 6146B series. 
Other transmitters won't work worth a "flip".  I have
seen transmitters that differ in serial number by less
than 10 in which the 6146B would work in one of them
and would not work in two of them!

I have worked on some Ranger I and II units that had
the 6146B inserted.  Frankly, everyone of them decided
to go "south" after a very short period of time.  I
have worked on various Heath rigs that have had the
6146B series installed.  Some of them worked without
problem but the majority of them did not!

It seems that the component tolerances, etc., seem to
add in a particular direction that allows the "B"
series to be used in one unit and not in another.

Collins had to modify the neutralization circuitry in
the S-Line equipment in order to be able to use the
"B" series (and the "W" series after 1964). 
Otherwise, the neutralization capacitor "burned up" in
at least 9 out of 10 transmitters.

One thing that I definitely do NOT recommend is mixing
the earlier types with the "B" in an r.f. circuit.  I
know that a few people have said that they have done
this without any problems.  But, in the VAST majority
of cases this is really asking for trouble!

In the DX-35 and DX-40, where the grid circuit is
really loaded down (and the final is NOT neutralized
in the original design) often you can "get away" with
running the "B" series (and "W" with a code date of
the 2nd half of 1964 or later).  But, sometimes this
is not the case and the final tube will short out and
sometimes take the transformer with it!  Since the
transformers in this equipment is run at the "ragged
edge" anyway, if the final melts down it often takes
the transformer as well.

I suggest that if you have to use the "B" series (and
"W" series) in a transmitter designed for the earlier
versions that you neutralize the final and watch it
closely for several days.  If the final will not
neutralize then the "B" tubes should be immediately
replaced with the earlier versions.  If the
neutralization "drifts" then the "B" types should be
replaced with the earlier versions.  If everything
holds, then that particular transmitter is "happy"
with the particular "B" tubes installed.  That is not
to say that they next time "B" tubes are installed
that they will work fine!  You still have to
neutralize, watch, etc.

Sideband transmitters are affected by the "B" problem
just like the AM/CW.

For those who haven't read the article on the 6146
family of tubes, go to either of the websites that are
listed at the end of this message.

Glen, K9STH


--- Ray Friess <rayfri at highstream.net> wrote:
> Glenn:
> Understand the rules for substituting 6146 tubes
> thanks to your article 
> on the subject.  I have a question though...
> How about in the older AM/CW Heath rigs, such as the
> DX 40, DX 100 and 
> the Apache ?    Adjusting
> neutralization is not called for when replacing the
> finals in those 
> rigs...    Do the same 6146 rules apply as in
> the sideband transmitters?    Could I use a 6146W in
> those am/cw rigs 
> without worrying about when the tubes
> were made?
> Ray  wa7itz


=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco


		
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