|[AMRadio] Subj change - HB designs|
ars.w5omr at gmail.com
Tue Jul 24 13:03:27 EDT 2007
> 811's make great modulators, don't they?
> I've had 2000 volts on 811A's with a 9v transistor radio battery for bias,
> just to see how/if they would work. They were very sensitive. Had to reduce
> the audio drive considerably from the previous 1100 volt/0 bias. No
> oscillation or any weirdness though. They actually seemed to sound a little
> cleaner, but that could have been anything - reduced drive - better impedance
> match - wishful thinking?
> Sounds like a good project Geoff.
Well, there's a multitude of reasons for going with 811's in the
modulator... heck, I might even run 4 of 'em, in push-pull parallel,
just to drop the plate-to-plate impedance down a little more, and
provide a little more ability for the modulator to handle a naturally
peaked asymmetrical voice. Not that I would -consistently- be running a
kW of Audio... just to have the ability to properly modulate the plate
of the final, without distortion.
Good Engineering Practices. Isn't that what it's about?
Besides, I might wanna change out the 4-125 for a 4-250 on Heavy Metal
night, and run 350w of carrier (with 4 811's in the modulator)
The more I think about it, the more I like that idea. a single 4-125,
modulated by (4) 811's in push-pull parallel with the option of going up
to a 4-250 or even a 4-400.
Check http://www.g8wrb.org/data/Eimac/4-125A.pdf for what Eimac says
about screen modulating the 4-125 final.
73 = Best Regards,
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