[AMRadio] Building


Geoff/W5OMR ars.w5omr at gmail.com
Sat Dec 1 21:07:59 EST 2007


Mike Sawyer wrote:
> Geoff said:
> A fine and fitting job for the RCA 1:1 modulation transformer, with
> 5,500 ohms on primary and secondary.
>
> **I wish I had said transformer.
>   

Got one here, but it's for a similar project.  BTW, it handles a pair of 
250TH's at 2000v 'just fine'. I -do- have to run a reactor choke, as the 
secondary is limited to 200mA of DC current.  I -believe- that's where 
core saturation occurs.

> If you want to get 'close enough', then, at 1500v, run 4 100TH's in
> push-pull parallel in the modulator for effectively 4400 ohms,
> plate-to-plate impedance, according to the Eimac tube data sheet.
> According to it, a pair of 100TH's in AB(1) has a plate-to-plate load
> impedance of 8800 ohms.  That's kinda high to work into a 5500 ohm
> transformer.  4400 ohms is -much- closer.
>
> **Doesn't that make quite a bit of Cg-p? You would need some large 
> neutralizing capacitors because of the combined C of the parallel tubes.

In class AB(1)?  Audio, not RF.  Four 100TH's to modulate a pair.

-- 
Driving your AM Rig without a scope, 
is like driving your car at night, without headlights. (K4KYV)

--
73 = Best Regards,
-Geoff/W5OMR



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