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Tio Pedro wrote:
Interesting! But be aware that the W6TC design has its flaws.

The first is that there are a lot of stages before you get to the
selectivity, which limits the dynamic range.

I was seriously considering adding a half-lattice crystal filter at the
first IF; the IF filter in the Heath HR-10 would be do the job. Now,
to find a junker! I'll probably end up cascading
IF transformers at 1600kc to improve the shape factor and hopefully
improve the dynamic range numbers for signals further out on the
filter slopes. I have the transformers, so I might as well use them
in this lifetime.

The second is that the
tunable LO operates at a high frequency on the upper bands and uses
plug-in coils, which limits the thermal and mechanical stability as
well as having different calibration on each band.

But each LO coil is hand calibrated for thermal drift I'd think the
Q would be much better using full-sized plug-in coils vs. phenolic
bandswitches and a compromised inductors. Ted's design ran the
LO on low side injection and used second harmonic injection for
the first mixer on the upper bands. That really sucks and kills the
idea of balanced beam tube in the first mixer. I agree, the design
is dated, and the advent of cheap IF filters killed the design. The
harmonic mixing scheme really bothers me.

6EH7 is a good tube. The receiver part of my rig (google my call) uses
one in the RF stage and one in the first IF, with a 7360 mixer.

Been, there, done that Getting to see a lot of nice RXs searching
the web!

One word: Don't. Use a bigger power transformer, or an auxiliary
heater transformer instead. The rx you describe is a big project, why
compromise it? With a separate heater transformer having its own power
switch, you could put the critical oscillator heaters on it and let
them run semi-continuously.


As you noted, the design is inherently limited..

Self-exciting the 6JH8 means the signal will go into the deflectors
rather than the grid. That's the opposite of usual receiver-mixer
practice, where the oscillator feeds the deflectors. I don't know what
the noise figure will be, but I do know that all the beam-deflection
receiver mixers I've seen put the signal into the grid for high gain
and low noise.

Check SSB Exciter Circuits Using a New Beam Deflection Tube,
by K2FF in the March 1960 QST. It is one of the better presentations
that appeared in QST. He also shows a self-excited product detector
circuit as one example. I'd think the advantage in the PD with
G1 injection might be improved BFO blowby rejection,
which could otherwise affect the AGC system?


I don't know if you really need a buffer stage on the BFO. A 6BH6 will
do the job. See above about where the signal goes.

The buffer could be used for a CF or phase inverter, if I wanted to
use BFO injection on both deflectors. I know only one needs to be
driven in practice.

First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and
buffer isolation.

How stable an oscillator is acceptable?

Buffer stage is recommended practice with the Pullen Mixer. It's easier
to use the pentode/triode, and ending not needing to use the stage, than
to add it later..

I'm not sure about the negative-feedback part but I do know the idea
was balance. And the 7360 deflectors were supposed to be biased a
couple dozen volts positive.

The negative feedback is mentioned in the QST article; it applies to
the product detector circuit where the deflector bias is taken directly from
the plates of the tube.

73 es GL de Jim, N2EY

Thanks for the comments..

Pete