[Fox_Tango] FT102 finals

[Dr. Gerald N. Johnson, electrical engineer]

Kenneth Crips wrote:
> 
> Re: valves to be matched
> 
> It's nice to have them matched but not 100% necessary.
> having a matched set makes it easier to neutralize.
> I would get 6146W's. These are the Mil-Spec version of
> the 6146B.
> 
> Kenneth Crips
> Amateur Radio Station W7ITC AMI-877

Not true.

Recent discussion on the Collins lists has turned up that some 6146W
were selected 6146A and some were selected 6146. So 6146W can be least
consistent.

Balance is not necessary for neutralization. Neutralization is based on
balancing the feed back capacitance of all the tubes in parallel.
Balance may be needed to get more equal sharing of drive voltage and
power output. Ideally each tube should have the same gain and the same
grid bias point for the idling current. When the tubes share in
supplying output equally more power is available without damaging any
one tube. When one tube does more than its share of the work that tube
will be fried first. This can be slowed by balancing. This can be
avoided by using 6146B and operating them at 6146 ratings.

73, Jerry, K0CQ
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