Mike Silva wrote:
The only difference in capacitance I see is Cgp, 0.24 pF for the 6146A
vs. 0.22 pF for the 6146 and the 6146B. Doesn't sound like any
difference at all, unless maybe the average values are quite a bit
different for the 6146B vs. the other two (but what would cause that?).
I don't question those who say there's a problem with some rigs, but
on paper all three tubes do seem to be the same (at the lower screen
voltage the 6146 is designed for). Apparently RCA thought the same
thing.

No conclusions, just ruminations...

73,
Mike, KK6GM


Hi Mike,

Neutralization is more than just interelectrode capacitance. It is
also affected by plate to everything outside the tube capacitance, and,
of course, the layout of the transmitter finals cage.

The plate of the 6146B is bigger than the 6146, or 6146A. It has about
33% more plate dissipation as a result. There is more coupling between
this bigger plate, and the outside world. As was pointed out by another
poster, it also requires a higher screen voltage.

In order to accomodate the 6146B, Collins completely redesigned the
neutralization circuitry on the S-Line transmitters, and the KWM-2(A).

The old circuitry had a 8-50pf PA neutralization capacitor, the new
circuitry has a 1.8-8.7pf PA neutralization capacitor.

If you put 6146B's in a KWM2(A) with the 8-50pf neutralization cap, you
will be replacing all of the neutralization circuitry in the near future.

-Chuck

Chuck Harris wrote:
Hi Mike,

Neutralization is more than just interelectrode capacitance. It is
also affected by plate to everything outside the tube capacitance, and,
of course, the layout of the transmitter finals cage.

The plate of the 6146B is bigger than the 6146, or 6146A. It has about
33% more plate dissipation as a result. There is more coupling between
this bigger plate, and the outside world.

I don't have an example of both tubes in front of me, but I don't
remember the plate structure of a 6146B being larger than a 6146(A).
Can anybody confirm that the 6146B plate structure is bigger? I
thought the higher plate dissipation was due to some combination of
different plate material and/or thicker plate material.

Is it possible that the Collins neutralizing capacitor range was
marginal to begin with, and that the higher power that the B tubes were
capable of just brought the problem to the surface? Just wondering...

73,
Mike, KK6GM

Mike Silva wrote:

Chuck Harris wrote:

Hi Mike,

Neutralization is more than just interelectrode capacitance. It is
also affected by plate to everything outside the tube capacitance, and,
of course, the layout of the transmitter finals cage.

The plate of the 6146B is bigger than the 6146, or 6146A. It has about
33% more plate dissipation as a result. There is more coupling between
this bigger plate, and the outside world.


I don't have an example of both tubes in front of me, but I don't
remember the plate structure of a 6146B being larger than a 6146(A).
Can anybody confirm that the 6146B plate structure is bigger? I
thought the higher plate dissipation was due to some combination of
different plate material and/or thicker plate material.

Is it possible that the Collins neutralizing capacitor range was
marginal to begin with, and that the higher power that the B tubes were
capable of just brought the problem to the surface? Just wondering...

73,
Mike, KK6GM


Hi Mike,

Collins went from a 7-50pf, to a 1.5-8.7pf. They made a few other tweaks
in the neutralization circuitry too. I have worked on both pre, and
post neutralization modification KWM-2's, and I can tell you that when used
with the proper tubes, the caps in either end up in the center of their range.

The KWM2A that is in my station right now has 6146W's, and the 1.5-8.7pf
neutralization cap, and the cap is in the center of its range. The heaters
on my 6146W's barely glow, so they are probably 6146A's. I don't recall,
are the B's dark heater too?

You get the same power out on the KWM-2 with any of the 6146 family, so I
don't think excess power output is the problem.

Collins said that the original neutralization circuitry tended to burn up
with the 6146B tubes. I'm willing to trust Collins to know the why's and
wherefores.

You can view the complete Heathkit SB101 ECO notes somewhere on the net. Heath
said there is something different about the 6146B's that requires changes
in the PA section. [ They also had a tremendous problem with variations in
other tubes made by different manufacturers. They out and out banned certain
manufacturer's tubes from use in their rigs.]

That the 6146B is different isn't just the rumblings of some flaky ham.
Collins and Heath made the necessary changes shortly after the B came out,
and long before I ever owned a rig using a 6146.

-Chuck

I had one of the first Heathkit HW-100's. I was on a waiting list before
they ever made the first shipment. Mine came with 6146B's. If there was any
change, it would have to of been made in the first few hundred. Like I have
said, the card that came with my HW-100 said they were equivalent. I've
seen dozens of them with both versions. They all worked just fine. I still
say it's nothing but an internet myth.

Darrell





Mike Silva wrote:

Chuck Harris wrote:

Hi Mike,

Neutralization is more than just interelectrode capacitance. It is
also affected by plate to everything outside the tube capacitance,
and, of course, the layout of the transmitter finals cage.

The plate of the 6146B is bigger than the 6146, or 6146A. It has
about 33% more plate dissipation as a result. There is more coupling
between this bigger plate, and the outside world.


I don't have an example of both tubes in front of me, but I don't
remember the plate structure of a 6146B being larger than a 6146(A).
Can anybody confirm that the 6146B plate structure is bigger? I
thought the higher plate dissipation was due to some combination of
different plate material and/or thicker plate material.

Is it possible that the Collins neutralizing capacitor range was
marginal to begin with, and that the higher power that the B tubes
were capable of just brought the problem to the surface? Just
wondering...

73,
Mike, KK6GM


Hi Mike,

Collins went from a 7-50pf, to a 1.5-8.7pf. They made a few other
tweaks in the neutralization circuitry too. I have worked on both
pre, and post neutralization modification KWM-2's, and I can tell you
that when used with the proper tubes, the caps in either end up in the
center of their range.

The KWM2A that is in my station right now has 6146W's, and the
1.5-8.7pf neutralization cap, and the cap is in the center of its
range. The heaters on my 6146W's barely glow, so they are probably
6146A's. I don't recall, are the B's dark heater too?



You get the same power out on the KWM-2 with any of the 6146 family,
so I don't think excess power output is the problem.

Collins said that the original neutralization circuitry tended to burn
up with the 6146B tubes. I'm willing to trust Collins to know the
why's and wherefores.

You can view the complete Heathkit SB101 ECO notes somewhere on the
net. Heath said there is something different about the 6146B's that
requires changes in the PA section. [ They also had a tremendous
problem with variations in other tubes made by different
manufacturers. They out and out banned certain manufacturer's tubes
from use in their rigs.]

That the 6146B is different isn't just the rumblings of some flaky
ham. Collins and Heath made the necessary changes shortly after the B
came out, and long before I ever owned a rig using a 6146.

-Chuck

Darrell wrote:
I had one of the first Heathkit HW-100's. I was on a waiting list before
they ever made the first shipment. Mine came with 6146B's. If there was any
change, it would have to of been made in the first few hundred. Like I have
said, the card that came with my HW-100 said they were equivalent. I've
seen dozens of them with both versions. They all worked just fine. I still
say it's nothing but an internet myth.

Darrell

Doing some casual research, I find that Heath did indeed know about the problem,
as early as January, 1978, but in 1979, when they had no choice, they gave approval
to use the 6146B.

-----------------------QUOTED FROM HEATHKIT's CHANGE BULLETINS---------------------

************************************************** *****************************
JANUARY 20, 1978
HW-101 BULLETIN NO:
SSB TRANSCEIVER HW-101-18

RF CHOKE IN FINAL PLATE CIRCUIT OVERHEATS OR
DIFFICULT TO NEUTRALIZE ON 10 METER & 15 METER BANDS

6146B tubes in the final amplifier may be causing this problem. To
correct, replace with 6146A tubes.

A label will be installed on the back panel of the HW-101 recommending
the use of 6146A tubes only. The 6146B tubes should not be used as a
replacement.
-----------------------------------------------------------------------------

------------------------------------------------------------------------------
NOVEMBER 20, 1978
HW-101 BULLETIN NO:
SSB TRANSCEIVER HW-101-39

IDENTIFICTION OF THE 6146A TUBES

The 6146A tubes [PN 411-75] used at V8 and V9 of this unit are marked
'6146A' in white ink on the side of the tube. These tubes may also have
'6146B' etched in the galss. These tubes have been reworked by G.E. and
are acceptable for use in the HW-101. Most tube cartons will contain the
following insert to explain the situation to the customer:

IMPORTANT INFORMATION;
THE TUBE SUPPLIED WITH THIS NOTICE IS TYPE 6146A, AS PRINTED ON ONE SIDE
OF THE TUBE, EVEN THOUGH THERE MAY BE A 6146B ETCHED ELSEWHERE ON THE
TUBE ENVELOPE.

ALWAYS REPLACE V8 AND V9 WITH 6146A TYPE TUBES

Replace the backing from this label and place the label at any convenient
location inside the cabinet top.
------------------------------------------------------------------------------


------------------------------------------------------------------------------
May 15, 1979
HW-101 Bulletin No:
SSB Transceiver HW-101-49

Changeover To 6146B Finals

The 6146A final amplifier tubes are no longer available from the
manufacturer. Future productions runs will use the 6146Bs. These are GE
brand tubes and have been tested in the HW-101. No difficulty was
encountered in neutralizing the finals; nor did the RF choke in the final
plate circuit overheat. The tube replacement label [PN 390-146] should
be removed from all units brought in for service.
-------------------------------------------------------------------------------

-----------------------QUOTED FROM HEATHKIT's CHANGE BULLETINS---------------------

I haven't yet found the bulletin mentioned by Zook, but everything he stated fits the
above bulletins.

To recap, he said that 1) heath forbid the use of 6146B's
2) Heath switched to B's when GE stopped making A's
3) Heath came to regret it.

I need to find the Bulletins from past 1979. That is where the meat is.

-Chuck Harris