The AM Forum

    Anyone know anything about this possible mod transformer? I believe it came from Stan, K1SJ, ex W1OKO, now SK. Top connectons (plate caps) are labeled 1 and 3. Bottom connections 2,5,6,7,8 + 9. Someone wrote on the side:

T-58
P-P 1625
8+9 lo z
6+7 hi z
2 ct caps
5 ground

 Aside from the obvious, I don't know much about it. Info? Thanks..........Larry

Looks like an Arc-5  plate mod xfmr, designed to match a pair of 1625's to another pair.  IIRC, there is a tertiary winding for  the screen.

Those modulators came in two  versions - screen modulated and plate modulated.  My very first plate modulated AM transmitter used one of those xfmrs.  Extremely poor low frequency response.

that is definately an ARC-5 mod transformer. It has 3 output windings. one for the plates, a tertiary winding to put some shake on the screens, and a 3rd winding for feedback.
       

I have one of those in my screen mod 4-1000 rig. I use the plate winding to mod the 4x1 screen, and the tertiary winding to shake the control grid biass, and the 3rd winding for a little feedback.
                         
                                                            The Slab Bacon

Dear "Slab Bacon", PSE may i get the diagram of the screen modulation of your rig using the 4-1000a?

Many thanks
John FG5FC

      Thanks for the info and comments. It was obvious that it was military of course. Its hard to believe that after all this time I have never owned an ARC-5 modulator. Have had receivers and transmitters, but no modulators. Anyone able to point me to a schematic of a modulator so I can see how this was used? And I would also like to see a schematic of this being used on the 4-1000 screen also. Thanks.........Larry

Here is the schematic.

http://hereford.ampr.org/millist/sch/md-7.gif

The Surplus Conversion Manual #3 discusses turning this unit into a screen modulator:

http://www.mines.uidaho.edu/~glowbugs/PDF%20files/Surplus/Surplus_radio_conversion_manual_vol3.pdf

       Thanks for the links, nice stuff there. But that schematic is not the right one. I did find the correct one elsewhere on the site in the ARC-5 section. There is a 354 page ARC-5 manual in there that had it......Larry

http://www.mines.uidaho.edu/~glowbugs/arc5pages.htm (http://www.mines.uidaho.edu/~glowbugs/arc5pages.htm)

Looking at page 148, it would be well to have also the driver transformer T-56, as it uses only the (carbon?) mike to drive the modulators through the transformer. Very nice!