HW-101 Tubes

[Glen Zook]

Here we go again! This question comes up at least once
each "quarter"!

The 6146 and the 6146A differ in the type of heater
(filament) and can be "mixed" in use (i.e. one 6146
and one 6146A in a DX-100).  There are no other
differences.  The heater in the 6146A was developed by
RCA and is called a "dark heater".  The type 8298 is
the same tube as the 6146A.

The 6146B is the same tube as the 8298A.  The 6146B is
a different tube from the 6146/6146A/8298.  Sometimes
they will work in place of the 6146/6146A, but often
they will NOT.  This is due to the different bias
requirements of the 6146B, different inter-electrode
capacitances, among other things.  Often it is
impossible to either neutralize the final in a rig
designed for the 6146/6146A or the neutralization does
not "hold" for very long (often less than an hour).

The 6146B/8298A have a very bad habit of producing VHF
and UHF parasitic oscillations which can cause all
sorts of problems including TVI as well as the tube
literally "burning" itself up.  This is when they are
used in circuits that were designed for the
6146/6146A.

Collins Radio had to modify production of the later
S-Line units to allow the military to use 6146B type
tubes.  This required a redesign of the neutralization
circuit which is in place in the later 32S3, 32S3A,
KWM-2, and KWM-2A units.  The earlier versions of
these models must use the 6146/6146A tubes.  The later
version can use all three types.

There is a "pulse" tube that is a very heavy duty
version of the 6146 and can be substituted without any
problems.  This is the 6293.  A 6293 will outlast a
"plain" 6146 by at least 5 times the life (over 10
times is not that unusual!).  We would "kill" back in
the late 1950s and early 1960s to get our hands on a
pair of 6293 tubes for our DX-100s, etc.

The 12 volt equivalent of the 6146 is the 6883.  The
12 volt equivalent of the 6146A is the 6883A/8032 and
the 12 volt equivalent of the 6146B is the
6883B/8032A/8552.  The same thing is true of these
tubes, do not replace the 6883/6883A with the 6883B
series of tubes.

Back in the late 1970s Motorola tried to replace all
of their 6883A/8032 tube stock with 6883B/8032A/8552
type tubes.  A very large number of Motrac units used
the 8032 and only the very "latest" versions used the
8552 tubes.  At the time I owned the Motorola
reconditioned equipment center for the south-central
US and we used, on average, over 100 8032 tubes a
week.  Just as soon as Motorola replaced the 8032 with
the 8552, we started having virtually all of the
Motrac units that were shipped to the customer arrive
with the tube envelopes "shattered" by "normal"
shipping.  We had never had this happen before.

The construction of the Motrac is such that the tubes
cannot be seen when the unit is assembled.  What was
happening is that in the 2 to 5 minutes that the radio
was being tuned and final QC'd, that they were
oscillating at UHF (parasitics) and the tubes were
getting so hot that the glass envelope was destroyed!

We told Motorola what the problem was.  However, they
refused to believe us until they had well over 1000
warranty complaints from their service stations.  It
cost them quite a lot of money in warranty repair
bills before they again started placing 8032 tubes in
the boxes marked 8032!

I have quite a number of "boat anchor" rigs that use
the 6146/6146A type of tubes including Collins 32S1,
32S3; Heath SB-110A, SB-401, DX-100, DX-35, Apache.  I
have owned rigs like the Knight T-150 and T-150A and
others that were designed for the older tube.
Frankly, all of them are much "happier" with the
6146/6146A instead of the 6146B.

Now, for the 6146W:  Unfortunately, some of these are
"ruggedized" 6146A tubes and the later ones are 6146B
equivalents.  The only way to tell is by the
manufacture date on tubes by a particular
manufacturer.  Unfortunately, to my knowledge, there
is no master list giving this information.  Each
manufacturer changed from the 6146A to 6146B
construction in their 6146W at different times.

I haven't seen a notice from Heath about using the
6146B tube.  However, several manufacturers, including
Collins Radio, originally said that it was fine to use
the newer tubes.  But, after a very short period of
time they found out different!

Thus, I would be very careful about using the 6146B
and the 6146W tubes in place of the 6146/6146A.  You
might "get away" with it.  However, you might also do
some damage to your final amplifier section.  If you
decide to try the 6146W, then be sure and neutralize
the final and check it after operating for an hour or
two.  If the neutralization remains OK for several
days, then you should be "home free".  But, if the
neutralization changes, then you need to replace the
6146W tubes with the 6146/6146A types.

Glen, K9STH

--- Lew28 at AOL.COM wrote:

Does anyone have any experiences using 6146W's in the
HW-101.  I am trying to find out if this is viable, or
will cause any problems.  I am not sure of the history
of tubes in this rig, but I believe that the original
specs were for 6146A and then Heath issued a bulletin
that 6146B was acceptable without mods.


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