[AMRadio] Low modulation Gates BC-1T


Thomas Adams quixote2 at ix.netcom.com
Sun Feb 25 17:33:16 EST 2007


At 03:34 PM 2/25/2007 EST, you wrote:
>
>I just confirmed that the grids of the 833s are indeed being fed 180 degrees 
>from each other.  One signal had more RF from the driver (only low B+ was
on) 
>than the other, but otherwise all seemed normal.
>
>Steve
>
>
>
>

Howdy, Steve!


OK. Thinking ahead a little bit on this, just in case...

If the mod transformer is toast, have you considered the possibility of
using a reversed plate transformer as a replacement until something better
comes along?

It'll work at lower power levels (I did it with a pair of 807s in the final
once) with an old TV set transformer; 110VAC primary as the secondary (to PA 
plate), and the HV plate winding as the primary (to P-P mod plates). It worked
well, and it didn't break down to the core with 900 VDC on the PA plates (as 
I half expected).

The big trick is finding the right turns ratio; with luck, the insulation
will do it's thing OK.

I'm just sorry I got rid of the 20V transformer and shunt reactor last
summer; a guy in Michigan was restoring a rig and not only did he offer me
a decent price for the pair, but he also came to get 'em!

As a last ditch effort...   in the W9LBB Surplus Heap I have a modulation
AUTOTRANSFORMER (Wilcox was big on those) that matched a pair of 450THs to
Gawd only knows WHAT in the final! The primary CT is internally tied to the
B+ supply side of the secondary, near as I can figure. It's about 150 pounds,
pretty ratty (needs derusting of the case bottom and paint, and a general
cleanup). The good part is that the impedances on primary and secondary are
clearly marked on the rusty case. The beast is oil filled, and the PA plate
winding has at least two taps as I remember.

If it'll do you any good, it's yours for the asking. Electrical condition is
unknown, but I assume it's a good pull-out; I got it when a Silent Key's
garage got cleaned out, along with those chokes you got. I think they were
from the same humongous AM communications transmitter.

But you CAN'T have the interstage transformer for the 450TH grids (matches
807 drivers, I assume in Class A).  ;o)   Good P-P interstage transformers, 
especially ones that'll handle 25 watts of audio, and almost impossible to
find these days!


Mr. T., W9LBB





 




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