[HBR] Re: HBR Digest, Vol 55, Issue 5

[Peter Bertini]

On Wed, Sep 17, 2008 at 10:12 AM,  <match at ece.utah.edu> wrote:
> On 17 Sep 2008 at 4:02, Peter wrote:
>
 n
> Over on the GlowBugs list we've been having a discussion about using the
> 6JH8 as a mixer. The problem with it is that it is rather dificult to drive the
> deflection plates. The capacitance is high, so the higher the frequency, the
> harder it is to drive.

That shouldn't be a problem, unless you're attempting to use an untuned
RF transformer. With a tuned circuit, the capacity would be part of the tuned
circuit. I thought about using the 6JH8 for the first mixer, but being balanced
harmonic mixing on the higher bands wouldn't work, and I couldn't figure out
how to achieve broadband LO injection. Having the mixer provide  IF rejection
at 1600kc would be nice, though.
>
> You scheme would work (theoretically) if you make the deflection plates part
> of the tuned circuit coupling them to the previous stage.

It's not really my "scheme," since it has been shown in the handbooks, with
very little practical information.  For the HBR, it would be simpler
to just apply
the signal to one of the deflection plates.

>
> I don't know how bad pulling would be. I suspect it would be large, but the
> only way to know will be to try it.

It's been done with tubes like the 6BE6...  I'm not sure if pulling
should be a problem,
but I've been advised that obtaining adequate injection levels might be???

>
> Marvin
> KA7TPH
>
Thanks

Pete