From Nameplate on Gates BC1-T Modulation Transformer

[k4kyv]

AM-30469         40-15000 cps

478 0084 000     F-12461


TERM                         VOLT                       VOLT-AMP

1-2-3                       2450 CT

4-5                          1800                          750

6-7                           80                             2

6-8                           110                           4

6-9                           155                           8

 
Electro Engineering Works   


"Volts" is given in RMS voltage. Multiply by 1.414 for peak voltage.  For example, 1800Vrms = 2545 Vp. The BC1-T is rated to run 2600 volts DC on the plate. 750 V-A would ideally be the same as 750 watts, the audio power required to modulate 1500 watts DC input, which is about what the BC1 series runs for 1 kw carrier out. The above figures calculate out correctly for 100% modulation with a sine wave tone.

The taps on terminals 6-7-8-9 are for applying a small amount of modulation to the driver stage to improve modulation linearity with the marginal grid drive to the 833As available from the pair of 807s in the driver stage.  The polarity must be correct so that both the rf driver and final are modulated in sync in the positive and negative directions.
 

[WA1HZK]

They like 3000 volts, 4 X 833's and will make 1500 watt carrier with full modulation all day.
Into a dummy load of course.

[KM1H]

Thanks Don.

Id heard from several that the mod xfmr was a weak link including the decades long chief engineer of the station that surplused the one I got the iron from. Its not something I want to chance blowing up.

Carl

[k4kyv]

I took three precautions with mine. (1) mounted the entire transformer on ceramic stand-offs to isolate the frame and core from ground. (2) Installed an adjustable spark gap across the primary winding plate-plate terminals. (3) Using metal spacers and  longer screws, moved the right-hand side panel an additional half-inch away from the frame of the cabinet, to provide additional space between the transformer winding and the panel.

The BC station where I once worked lost a plate transformer when the HV arced through the black paper that covers the winding to the 220 volt a.c. power line feeding the primary, that had somehow managed to migrate too close to the winding after the plastic cable clamp that was supposed to anchor it to the floor of the cabinet had deteriorated with age. You don't want anything metallic to get too close to those unprotected windings, and at least in my transmitter, the spacing between the mod transformer and side panel was a tiny fraction of an inch - too close for comfort.