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

[Peter Bertini]

O
> Pete quoted me:
>>> My favorite AGC circuit uses a plate detector with almost any of the
>>> common triodes with the cathode returned to a negative bias of 50
>>> volts or more <SNIPPED>
>
>


Hi Walt

I've been thinking about the plate detector, and I've read some of your other
comments where you had problems with attack times when going with too
long a time constant... I believe you used paralleled RC combinations to
provide both a fast attack, another for a slow decay...

I was thinking of using both sections
of a 12AV7 (low plate R) for dual plate detectors. One section would feed a
faster time RC time constant, the other a slower RC time constant; and I'd
end using low-voltage drop diodes to "OR" the two AGC signals to the high
impedance AGC path.  I could draft the schematic and post a link; think the
idea has merit?  In fact, I could switch the slower release RC section
to provide
a faster AGC release for CW? Also, does paralleling the triodes halve the
plate resistance?

Second question for the group:  I'm thinking of cascading dual R-23 IFTs at the
85kc IF; first two will follow the 2nd mixer, and two cascaded
transformers between
the 1st and 2nd IF amplifiers.  I'm not sure anything would be gained by adding
two more between the plate of the second IFA and the mode detectors?  This
begs the question, what would be the best means to vary the BW of the 85kc
IF stages?    Several ideas come to mind:  a mechanical linkage to move the
coils in or out (Silvertone actually did this in their better home
receivers back in
the 30s), or would switching different values of coupling caps between the
cascade stages a better means? I suspect I'll need to keep the coupling tight
or the selectivity might be too sharp for AM or SSB.

Pete
>