[ARC5] HF Converter - the mixer.

[Bobby Drummond]

The Pullen mixer sure reminds me of a two triode Butler oscillator.


73 de AK4JA

On Thu, Mar 17, 2022 at 3:10 AM Tom Lee <tomlee at ee.stanford.edu> wrote:

> Hi Ken,
>
> Your mention of the Pullen circuit takes me back in time -- thanks! It
> is indeed an excellent mixer, and particularly attractive for upgrading
> classic VT receivers. It certainly exhibits better noise performance
> than do non-triode circuits. It still suffers from spurious responses to
> image frequencies, but the laziness of a tube's characteristics
> (relative to a transistor's) means that the conversion gain to the image
> terms will be quite a bit lower than the primary conversion gain. As
> long as the interference environment is benign, or the receiver is
> preceded by a good preselector, the image problem can be managed well.
> LO feedthrough is still a problem for this circuit (as for any
> single-balanced design), but brute-force filtering handles that.
>
> If one were carrying out a blank-sheet design for maximum dynamic range,
> I'd still elect a more modern double-balanced architecture. But if I
> wished to stay with the hollow state, I'd probably choose the Pullen for
> all but the simplest, low-tube count receivers. And if I wanted to
> upgrade an existing receiver, retrofitting it with a Pullen mixer would
> be a great idea.
>
> Thanks very much for posting those links!
>
> -- Cheers,
> Tom
>
> --
> Prof. Thomas H. Lee
> Allen Ctr., Rm. 205
> 350 Jane Stanford Way
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu
>
> On 3/16/2022 22:54, Kenneth G. Gordon wrote:
> > I find it somewhat odd that so few people consider the so-called "Pullen
> Mixer" for such an
> > application.
> >
> >  From my study of that mixer, it seems to me to be a nearly perfect
> mixer for this purpose.
> >
> > I wonder if Dr. Tom would consider commenting on this?
> >
> > Here are some links to it which I have published on my website for a
> number of years.
> >
> > http://www.w7ekb.com/glowbugs/rx/receivers.htm
> >
> > ...at 9) about half-way down the page...
> >
> > and
> >
> > http://www.w7ekb.com/glowbugs/rx/Pullen/PullenMixer.pdf
> >
> > http://www.w7ekb.com/glowbugs/rx/Pullen/75A4Pullen.pdf
> >
> > One thing that is not clear from any of the above is that to properly
> implement this mixer will
> > require 4 triodes, not 3, 1 of which would have to be a cathode-follower
> between the
> > triode-HFO and the mixer-proper.
> >
> > I had planned to use two 7963 submini dual triodes in my implementation
> of this circuit.
> >
> > These could be mounted on an octal tube base, with other components, and
> simply plugged
> > into, say, an "ARC-5" receiver in place of the 12K8 for instance. Other
> parameters would
> > have to be "tweaked", of course.
> >
> > It also appears that the higher the transconductance of the triodes
> involved, the better this
> > mixer circuit works.
> >
> > Ken W7EKB
>
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-- 
73 de AK4JA
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