[HBR] My approach to the HBR... Suggestions?

[Peter Bertini]

On Thu, Sep 11, 2008 at 7:13 PM, Ian Wilson <ianmwilson73 at gmail.com> wrote:
> Sounds exciting :)
>
> One thing I've pondered about the hang AGC circuit used in
> several variations (e.g. in the Sideband Handbook): would it
> be possible to do without the 1:3 audio transformer by using
> a higher gain stage (e.g. pentode instead of triode) and
> tapping up the plate load resistor? The 3x output (plate)
> and 1x output (tapped 2/3 up the load resistor) would be
> RC coupled to the appropriate AGC diodes.
>
> 73, ian K3IMW
> ************************************

The audio transformer only provides cutoff bias for the AGC time delay triode.
I don't see why the circuit would be overly critical, since the problems seem
to be more related to the AGC attack times and overshoot.  The grid bias
resistors, and grid bypass caps, might be more of a concern?  I've read that
typical values can cause a 1 ms AGC attack time delay, and with the larger
value bypass caps neededfor an 85kc IF might that problem even be worse?

 I'm thinking of RC coupling the plate of the 12AU7 Audio AGC amplifier into an
ARC-5 audio transformer(at the unused CT on the primary), with a full
wave detector
across the full winding; this would be to develop the cutoff bias for the
12AU7 triode used for the AGC delay.A bit of overkill, but the ARC-5 transformer
is collateral salvage from the RX's used to supply the IFTs :) i.e. cheap, free
and they seem to be of very high quality.

That would avoid adding an additional stage to amplify  the 85kc signal
 for the sake of creating delay cutoff bias, as was suggested by Goodman
in his classic QST article.  On the other hand, instead of using an audio
derived half wave  detector for the AGC voltageI'm more inclined to try a simple
 RF derived detector using high back resistance diodes or a 6AL5. RF AGC
should be much faster than the  halfwave detected audio derrived AGC shown
in the HBR featured in the 17th edition of Orr's Handbook?

>From my viewpoint, a good hang AGC system is a key
part of the RX; and I suspect there were a lot of tradeoffs due the BFO
signal getting back into the AGC and affecting the gain...  Ted's HBRs were
at the cutting edge of the SSB revolution and a lot of work was left to be
done.

Pete