[HBR] Under construction HBR-??

[Darrell, WA5VGO]

I have been using quality (Allen Bradley) carbon pots in several HBR's in 
both the gain controls and the S meter circuit for years without a single 
failure. The need for wirewound pots seems to be overstated.

A hang AGC is the only way to go. The circuit I'm using is pretty much 
straight out of the ARRL Handbook and it's a vast improvement over the one 
used by Ted. I found that feeding it from the IF worked much better that 
from the audio.

Keep us posted.
Darrell, WA5VGO



At 09:54 PM 3/15/2004 -0500, Bill Higgs wrote:
>Hello fellow solder junkies,
>
>
>
>Question two regards the gain controls on the RF, Mixer, and IF amps. I'm 
>looking seriously at the hang AGC circuit, which appears to have provision 
>for manual or concurrent gain control by feeding a negative voltage into 
>the circuit at the recovery diode and/or the agc line (I'd isolate it 
>through another diode, though . . .) The 5W wirewound resistors in the 
>values W6TC specified are practically "unobtainium" nowadays, and most 
>catalogs jump from 2W to 12W. Digi-Key advertises 5W CTS wirewounds at 
>$2.50 each, but the values run 1K, 5K, 10K and 25K. Since the point of 
>this pot is to adjust the cathode bias from zero to some positive voltage 
>(thus biasing the control grid negative), I have also thought of 
>developing a negative voltage from a doubler off the filament line, and 
>using a higher value pot to control a negative voltage to the tubes via a 
>diode (my thinking is that as the grid is a higher impedance point, less 
>dissipation on the part of the pot. Other idea (not quite Kosher), is to 
>run the cathodes off a power transistor (2N3055?) controlled by a smaller 
>pot, since the cathodes are fully bypassed. This keeps the solid state out 
>of the signal path, at least. But does put silicon inside the box, which 
>sort of defeats where we're going, doesn't it?