[ARC5] Help a Dummy Out on Modulation.

[mac]

Note that the grid bias for the modulators is derived from the PA grid  
resistor.  Check to see if there is a significant bias variation with  
different PA loads.

Dennis D. W7QHO
Glendale, CA



On Feb 8, 2010, at 1:09 PM, David Stinson wrote:

> I don't understand something, so thought I'd ask the
> people smarter than me...
>
> Take a look at this diagram of a BC-230 transmitter:
>
> http://home.netcom.com/~arc5/SCR-AH-183/BC230TX.JPG
>
> If operated and tuned according to the manual, using the
> called-for 4-ohm/100pFd phantom antenna and using a
> normal, well-working carbon microphone, I can't get more than
> 30% moduation and about 40 mils of antenna current.
> Tubes are good.
> Now, I understand about the modulators not
> delivering enough power to get 100% at full load, and the manual
> says to keep the loading down so you can get more mod.  However-
> no matter where I load the rig, light or heavy, tuned or mistuned,
> I still get about 30% mod, unless I yell.  Even more funny- if I use  
> an
> external
> antenna tuner, a wire antenna and just tune for maximum "smoke,"
> I get about 1.2 amps antenna current and nice, 100% mod!..... (tilt!).
> To add more "huh?" to the mix- when I use one of the xtal-control
> coil sets with a 3880 KC crystal installed, I get less power out
> (probably due to lower grid drive), but I can over-modulate.
> I'm scratching my pointy head on this one, guys.
> What is it I don't understand here??
>
> 73 Dave S.
>
>
>
>
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