[AMRadio] Low modulation Gates BC-1T

Geoff/W5OMR ars.w5omr at gmail.com
Mon Feb 26 01:14:44 EST 2007

SBJohnston at aol.com wrote:
> Deep in the bowels of my junk I found some resistors for a test of the whole 
> modulation section of the Gates BC-1T.  I put five large-ish (each like a roll 
> of quarters, maybe 50 watts?) 800-ohm wirewounds in series across the 
> secondary of the modulation transformer.  Thaty would seem a good load: 4000 ohms.  I 
> put an RMS voltmeter across one of the resistors in the stack.
> Applied tone to the input... enough drive to produce 200 mA of combined 
> modulator current produced about 100 volts across the one resistor.  400 mA got me 
> about 200 volts.  And the tube plates were medium-glowing at 0.2 A (what I'd 
> consider normal for 833 modulators) and quite brightly glowing (more than I'd 
> like to see on an 833) at 0.4 A.
> Didn't run it too long, but after I shut it down the resistors were hardly 
> warm at all.  
> Steve WD8DAS

Hate to say it, Steve, but I think your modulation transformer is fried.

Had a similar thing happen with a Ranger I mod xfrmr... plenty of plate 
current on the 1614's... excessive, in fact.  Just no, or very low 
modulation.  Turned out be a blown mod tranny.

Good Luck!

-W5OMR (home for 2 days)

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