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