differences in 6146 A and B

[Glen Zook]

Regardless of what others are telling you:

There is a definite difference between the 6146 /
6146A / 8298 and the 6146B / 8298A.

In some rigs, the 6146B / 8298A can be used as well as
the 6146 / 6146A / 8298.  However, this is more often
not the case.

The 6146B series has different bias requirements,
screen voltage requirements, etc. which often causes
parasitic oscillations in the VHF region that, in
turn, cause the tubes to overheat (as well as causing
TVI, etc.).  Many times it is impossible to neutralize
the 6146B series when used in place of the 6146
series.  When they can be neutralized, this is often
for only a short period of time, then the
neutralization has to take place again (sometimes
within minutes) as the tubes "age".

Collins, in their S-Line equipment, had to make
modifications in the later 32S3 / KWM-2 series to
allow the military to use the 6146B series tubes.
This involved major changes to the neutralization
circuitry.  On the earlier models (32S-1, 32S-2,
32S-3, 32S3A, KWM-2, KWM-2A) equipment 6146B tubes
should NEVER be used unless the neutralization
circuitry is changed.  If you try to use the 6146B in
transmitters that have not been modified, the
neutralization components will overheat and "burn up".

I have all sorts of equipment that use the 6146 /
6146A / 8298 series of tubes including DX-35, DX-100,
Apache, Seneca, SB-110A, SB-401 in the Heath and
32S-1, 32S-3 Collins (as well as other rigs). All of
these are MUCH happier with the 6146 / 6146A series of
tubes.

The 12 volt equivalent of the 6146 / 6146A are the
6883 / 6883A / 8032 and of the 6146B are the 6883B /
8032A / 8552.  Motorola used the first series (8032)
in the Motrac mobile radios from the "A" through "D"
series of the HHT radio.  The "E" model of the HHT,
the LHT, and MHT series used the later (8552).

In the late 1970s Motorola decided to simplify their
parts stock by only supplying the later (8032A / 8552)
tubes.  Even though the tube boxes said 8032, they
actually contained 8032A / 8552 tubes.  At that time I
owned the Motorola reconditioned equipment center for
the south-central US and we were "turning out" from 10
to 50 Motrac units a day.  In the Motrac units it is
impossible to see the amplifier tubes since they are
enclosed in a metal heatsink.  It turns out that in
virtually all of the units that were designed for the
8032 tubes  (some used them only as drivers and some
as both driver and final) when replaced by the 8032A
tubes the tubes were getting so hot from parasitic
oscillations that the glass was actually anealed in
just a few minutes of operation and broke at the
slightest shock.

Even tuning them up on the bench was enough to cause
this problem.  We had well over one hundred arrive at
their final destination with the tubes already
shattered!  It took several weeks to convince Motorola
that the problem was in the different type of tubes.
It was not until they received well over a thousand
claims from the field that they admitted their mistake
and went back to supplying the correct type of tubes.

Unfortunately, the 6146W type of tubes were/are made
in both the 6146A and 6146B types with no
differentiation of which is which.  That is one of the
reasons that Collins had to modify their equipment to
use both types of tubes.  The earlier 6146W are 6146A
and the later are 6146B.  It depends on the
manufacturer as to exactly what date they made the
change on.

I would be very interested in obtaining the date-code
information from the various manufacturers as to
exactly when the change was made from the 6146A to the
6146B manufacture in the 6146W.  At least then, by
reading the date code printed on the tube, you would
have a pretty good idea as to which version it really
was.

You can always replace a 6146B series tube with the
6146 / 6146A type.  But, to go the other way is, in my
experience, risky.

Another tube that is fairly "rare" to find, but is an
excellent replacement for the 6146 / 6146A is the
6293.  This tube was made for "pulse" operation with a
power output of at least 1 KW!  Since pulse is a very
low duty cycle this is quite possible.  The 6293, when
used in place of the 6146, has an operational life of
several times that of the 6146.  The operational
specifications are identical to the 6146.  Back in the
early 1960s, we would almost "kill" to get a set of
6293 tubes for our DX-100s, etc., since they never
seemed to go bad.

A few weeks ago, I was fortunate to obtain a pair of
the 6293 tubes.  I haven't decided which rig to put
them in!

Anyway, unless the equipment was originally designed
for the 6146B series, I would be VERY careful when
using 6146B tubes.  I have found very few transmitters
that will work correctly with them unless
modifications are made, especially to the
neutralization circuitry, the screen voltage, and the
bias (this is adjustable in most rigs so is not that
big of a problem).

Glen, K9STH



--- Larry Bratcher <lbratche at SWBELL.NET> wrote:

I want to replace the finals in my SB-102.  I can find
6146B tubes locally but not sure if they will work or
not.  What is the difference in the 6146, 6146A, and
6146B?  Hope this is not a dump question!


__________________________________________________
Do You Yahoo!?
Make a great connection at Yahoo! Personals.
http://personals.yahoo.com

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html