[AMRadio] Mod transformer turns ratio

Geoff/W5OMR ars.w5omr at gmail.com
Sat Nov 17 18:00:18 EST 2007

jeremy-ca wrote:
> Don, it is rated at 7.34KW and weighs in around 250-300#. Came from a 
> 10 KW Martin BC TX; PP 4CX5000A's modulating another pair. No other 
> markings on it other than the mfg (Avdin Energy Corp) part # and date 
> code of 7752.
> Its in oil and about 17" square and maybe 22" high.
> Serious overkill but the price is right and Ive been looking over a 
> year for something. The size doesnt bother me, just as long as I can 
> use it. Maybe I should dust off the 304TL's and forget about the 810's?
> OK on the choke requirement. I'll start looking once I determine 
> exactly what the heck Im doing.

I wouldn't worry about the choke.  If you've got a modulation 
transformer for a pair of 4CX5000A's, that thing should be capable of 
some SERIOUS current!

*Plate Modulated RF Power Amplifier, Grid Driven, Class C Telephony - 
Carrier Conditions*
/Absolute maximum ratings/
DC plate voltage 5500 V
DC screen voltage 1000 V
DC grid voltage -500 V
DC plate current 2.5 A
Plate dissipation 3.5 kW
Screen dissipation 250 W
Grid dissipation 75 W

/Typical Operation/
DC plate voltage 5000 V
DC screen voltage 500 V
Peak AF screen voltage (100% mod.) 450 V
DC grid bias voltage -400 V
DC plate current 1.4 A
DC screen current* 0.26 A
DC grid current* 0.05 A
Peak rf grid voltage* 520 V
Grid driving power (calculated) 25 W
Plate dissipation 1100 W
Plate output power 5800 W

*Audio Frequency Power Amplifier or Modulator, Grid Driven, Class AB1*
/Absolute maximum ratings/
DC plate voltage 7500 V
DC screen voltage 1500 V
DC plate current 4.0 A
Plate dissipation 6000 W
Screen dissipation 250 W
Grid dissipation 75 W

/Typical Operation (two tubes, sinusoidal waveform)/
DC plate voltage 5000 7000 V
DC screen voltage 1250 1250 V
DC grid voltage** -280 -325 V
Zero-signal plate current 1.0 0.70 A
(*RESTING/IDLING current, is 1AMP!  SEE THAT?  HOLY SMOKES!  Twety one 
point seven two Jig-a-watts?!  Get the D'Lorean!*)
Maximum signal plate current 4.40 3.65 A
Maximum signal screen current* 0.33 0.24 A
Peak AF grid voltage 240 235 V
Driving power 0 0 W
Load resistance plate-to-plate 2370 4100 Ohms
Maximum signal plate dissipation 4200 4200 W
Plate output power 13.5 17.5 kW
* Approximate values ** Adjust for specified zero-signal plate current

I just don't think you're going to have any problems with the 
transformer core being saturated by a measly/paltry few hundred 
milliamps.  ;-)

73 = Best Regards,

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