Apache TX-1 "RF Hiccup" Puzzle

[Peter A Markavage]

I also have FBTO but unfortunately, it doesn't list the CQ Ham Clinic
tips. The article on putting holes in the outside cabinet is good for
getting at the side and under chassis adjustments. Also, there was an
article on correcting "wrong-way" grid current readings. One or two
others, but nothing addressing your problem.

Check also the clamp tube adjustments and also the NE-2 neon lamp. If
that lamp is intermittent, it might burp as you power down the plate
supply. The only way to check this is to pull the chassis out, flip it on
its side, and watch it as you switch the plate supply on and off.

Pete, wa2cwa
ps Garey - the Apache already has a spotting switch. I believe the
article had to do with some minor rewiring of the spotting switch
circuitry.

On Thu, 24 Jun 2004 14:47:25 -0400 Garey Barrell <k4oah at MINDSPRING.COM>
writes:
> Lin -
>
> FBTO comes up with about 4-5 QST references in the 59-60 years,
> but none refer to this problem.  Things like drilling small holes
> in the cabinet to allow some adjustments without removing TX from
> the cabinet, adding a spotting switch, etc.
>
> Just a guess.  I don't have a schematic of the TX-1, but is it
> possible that the bias supply, (cutting off the low level stages
> on "key-up",) filter cap is bleeding down before the plate supply
> filter?  Possibly a "dried out" high ESR filter cap in the bias
> supply....  The result would be "keying" the transmitter, which
> would quickly dump whatever remaining charge there was in the HV
> supply.  Or, worse yet, possibly an open bleeder on the HV supply
> causing it to discharge too slowly?
>
> Easy to check, (or at least as ANY task involving opening up the
> Apache is easy, see drilling extra holes above! :-),) just
> parallel a large electrolytic across the bias supply.  Or check
> bleeder resistors on HV.
>
> Let us know what you find.
>
> 73, Garey - K4OAH
> Atlanta
>
>
> >>On Wed, 23 Jun 2004 20:54:51 -0700 digital-conjurers at ADELPHIA.NET
> writes:
> >>
> >>Have an Apache TX-1 running AM only with an unusual problem:
> >>
> >>About 250 milliseconds after unkeying, there is a small "RF Burp"
> or
> >>small RF pulse of very short duration (100 ms or less), and small
> >>energy, that comes out of this transmitter.  This is especially
> >>puzzling, given:
> >>
> >>1.  The finals seem perfectly neutralized
> >>2.  Voltages, tubes, everything checks out as nominal
> >>3.  Coax routing seems very orderly
> >>4.  The complaint _slowly disappears_  as you tune the final tank
> >>circuit slightly off the resonance dip; i.e. if you're dipped at
> >>200ma, and slowly swing up to, say, 240ma, the phenomenon goes
> >>away.
> >>5. SWR is low; even does it on the dummy load.
> >>
> >>[BTW we're using 6293 industrials instead of convetional 6146's.
> >>(The primary difference between these and the "normal" 6146 is
> that
> >>the plate is much "heavier" in its construction. )]
> >>
> >>So, the sequence is:
> >>
> >>1. Unkey, the Dowkey releases, all power meters swing to zero,
> 250ms
> >>later there's that >100ms RF "hiccup", then all is fine.
> >>
> >>Wierd.
> >>
> >>Ideas?
> >>
> >>Thanks to the group in advance,
> >>
> >>Lin/KJ6EF
>

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