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

[Hopperdhh at aol.com]

Pete,

I have never liked audio derived AGC.  As you tune  through zero beat on CW 
the gain goes up and down.  Pumping problems are  hard to control.  You will 
not be able to achieve the kind of attack times  you can with IF derived AGC.  
You may need a separate IF amp for the AGC to  help keep out the BFO signal.  
At any rate take special care to isolate the  BFO.  I built an SSB transceiver 
once that had excellent AGC  characteristics after studying the time constants 
(different for RF vs. IF) used  in the Drake TR4.

Keep in mind that the 85 Kc ARC-5 IF cans are  relatively low Q -- about 60 
if I recall.  Bob Drake was my hero when it  came to filter design.  The Drake 
2-B has only 4 tuned circuits at 50 Kc,  but the Q must be pretty high.  There 
are cores available today to take  that approach, but the ARC-5 coils will 
work.  Since you have them, and  have space for them, give 'em a try.

I like your idea of using more tuned  circuits and sweep tuning them.  You 
might also try LTSpice (free download  from www.linear.com) to model the filter. 
 Its easy to try different  coupling circuits and values once you have 
measured the L and Q of one of the  coils.  I would assume 1 megohm for the input 
and output tube  loads.

You will probably need to remove turns from the 1415 Kc cans to  move them up 
to 1600.  You may not need 4 cans at 1600, I would breadboard  up a one (or 
two) tube test circuit to see what kind of response two cans have  at two times 
85 Kc away from the peak.  (LTSpice could be used here  too!)  Also, using 
1605, or 1655, etc., may be a better choice to reduce  interference from BC 
stations.
 
Best of luck -- have fun,

Dan K9WEK
 



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