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