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August 20th 03, 05:07 AM

(Space Charge) wrote:
Need some informed opinion, as I've heard various things about finals
that use two 6146's, like my TX-1 Apache:

1. Make sure the transconductance on both is very close.

2. Make sure the plate current on both is very close.

1 and 2 amount to the same thing, with practical test setups.

3. Make sure BOTH are close, especially the plates, which should be
within 2ma, and _both_ should be either 6146, 6146A, or 6146B. Don't
mix types.

You *definitely* want the same type tube. There are
*significant* differences between a 6146A and a 6146B, and they
simply cannot be considered as the "same" tube. One possible
problem is that tubes labeled 6146W might be either an 6146A or
a 6146B. If a 6146W was made prior to 1964, it is a 6146A; if
was made after 1964 it is a 6146B. If it has a date of 1964, it
depends on which which company manufactured it and the month of
manufacture (meaning you usually can't find out which it might
be).

4. None of the above matter, so long as both test well on a good
checker. (I use a Hickock/'Hiccup' 539B.)

Can someone shed some light on this? What's correct?

The best test would be to put the tubes into a transmitter and
measure the IMD. Even hams with the appropriate equipment are
likely to balk at going to that much trouble though! Next best
would be to measure the plate current at several points between
peak power and no power.

Last, but entirely suitable (with results depending on the
particular test set) is to plug them into a test set and record
the results.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

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