[Hallicrafters] 6146 tubes for HT-32

[Glen Zook]

The 6146B is really a different tube from the 6146 and
6146A.  Not only is is rated at 33% more power input,
the interelectrode capacitances, bias requirements,
etc., are somewhat different from the 6146 / 6146A.

When RCA introduced the 6146B in the spring of 1964,
they stated that the 6146B was directly
interchangeable with the 6146 / 6146A.  Many of the
manufacturers including Collins and Heath took RCA "at
their word" and put out information that it was "OK"
to substitute the 6146B for the earlier tubes. 
However, in a very short period of time problems
started happening.

In the case of the Collins S-Line and KWM-2
transmitters, the neutralization components started
"burning up".  Similar things happened with other
brands of transmitters as well.  What is happening is
that the 6146B often "takes off", oscillating at VHF
and UHF frequencies (parasitics) and either the
neutralization components, or, more likely in many
transmitters, the tube itself "self destructs".  Since
the military wanted to be able to use the 6146B
equivalent 6146W tubes in all of their equipment,
Collins had to redesign (and retrofit the military
S-Line and KWM-2 units) the neutralization circuitry. 
With the changes, the modified units can use all three
members of the 6146 family.

The best test to see if the 6146B will work in an
individual transmitter is to see if the final will
neutralize.  Often it will not.  If it does
neutralize, then watch the neutralization for several
days.  If the neutralization does not "hold", then the
6146B tubes should be replaced with the 6146 or 6146A
series.  If it does hold, then that particular
transmitter is "happy" with the 6146B.

There are definitely older transmitters that were
designed for the 6146 / 6146A that will work with the
6146B.  However, two identical transmitters, one might
work with the 6146B and the other will not.  Thus, it
is not recommended that the 6146B be used without
paying careful attention to make sure that the final
is not "taking off".

Motorola used the 12 volt equivalent of the 6146A in
the HHT series Motrac (until the "E" model).  In the
late 1970s Motorola tried to replace the tubes with
the 6146B 12 volt equivalent.  The results were
disasterous!  The tubes were failing within minutes! 
Motorola had to begin supplying the correct series
tubes again and to "eat" many thousands of dollars in
repair claims by their service stations.  This I know
since I owned the Motorola reconditioned equipment
center for the south-central US at the time.  We were
the first to discover this problem.  It was caused by
the fixed neutralization of the Motrac and the fact
that the 6146B equivalents were a different tube.  To
change the circuitry in the units would violate type
acceptance as well as being "time consuming".  Thus,
Motorola had to again supply the correct tube.

Many of the Johnson transmitters definitely do not
like the 6146B.  The same thing with the Heath. 
Again, a relatively few will work fine with the 6146B,
but, the majority will not.

Glen, K9STH




--- rdhalste <rdhalste at tm.net> wrote:

> Why?
> 
> In the past, I've used anything that I could get to
> fit the socket that said
> 6146 and have seen no problems, but that was years
> ago.  I'm just getting
> back into equipment that lets me play and heats the
> shack at the same time.


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