[Fox_Tango] Re: Fox_Tango digest, Vol 1 #5 - 8 msgs

[W Sanders]

Everyone agrees that a tube-eating FT-101 ought to have it's neutralization
checked - I checked mine using the procedure in the manual and it's OK. I used
the "equal rise" method and I see my plate dips coindicing with my max power
on all bands so I assume it's OK. To do better would require the "signal
generator feeding RF back into the transmitter" (*) method. I think Tom KD4WOV
is right - 6JS6Cs will just not take high duty cycles. 

I posted something a few months ago on the 10pf neutralization mod. If you do
the math you'll see that replacing the 100pf cap with a 10pf cap does not
change the capacitance much since the fixed cap is in series with a 10pf
variable (I am assuming the schematic is right and the air variable is 10pf
max.) I think maybe there are other reasons for the 10pf mod - IIRC Yaesu
issued a service directive for it, even with original finals - like maybe a
10pf drifts less, it fails safe if the air variable shorts, or it makes the
neutralization mod less "twitchy".

I did get RF feedback in the finals once when I was adjusting neut - it was
not pretty - a started getting strong static on band 10C in receive mode -
noticed a "hot" smell - I took me about 3 seconds to figure out what was
happenening and I detuned the oscillation by switching bands. No damage was
done, but a few more seconds and I definitely would have smoked not only the
tubes but also the coils in the output PI network.

-Wiley KF6IIU

(*) While off. This is described in the ARRL handbook.