[Milsurplus] [ANGRY-9] GRC-9 Receiver AF Amp bias voltage tests

[mac]

Been running GRC-9s for years with both live and dead bias batteries  
and my experience matches Tim's.  The BC-1306 that preceded the GRC-9  
derived bias for the AF amp tube from the receivers HF oscillator  
circuit (no battery).   Different oscillator configuration  used in  
the GRC-9, though, which does not readily lend itself to such an  
approach but maybe worth another look.

Dennis D.  W7QHO
Glendale, CA

***************
On Dec 22, 2013, at 4:47 PM, Tim wrote:

>
> OK, you guys got me thinking that I needed some DATA on this bias  
> voltage requirement.  So I did some quick experiments, with and  
> without the proper bias.
>
> Basically at low audio output speaker levels, applying or removing  
> -4.5 volts grid bias made no observable difference to a sine wave  
> signal as seen on a scope.  Nor in my hearing any difference.  (my  
> hearing is shot  LOL)  There was only a very small difference in  
> receiver B+ draw.  (couple of hundred microamps increase with no  
> bias - on top of 10 milliamps).
>
> At high (loud) audio levels bias makes an observable, positive  
> difference  - With bias, the output looks and sounds "better".   The  
> distortion (without bias) observed presumably happens when the audio  
> input signal drives the grid positive.  The results were not TOO  
> surprising.....
> For a combat vehicular radio what would likely need to be "turned  
> up" often, I can see why the designers chose the additional  
> complexity of the bias battery.
>
> Some further thoughts and my test details at the bottom end of this  
> post under "Problem Areas": http://www.n6cc.com/angrc-9-radio-set
>
> For me, I am sticking with the bias battery in my sets although the  
> performance difference is minor the way I use them.  "It's an  
> Engineering Thing"  LOL
>
> FYI, Tim
> N6CC
>
>
>
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