The modulation transformer used in the ART-13 can still be found at hamfests and on the surplus market. It has been used widely in homebrew modulators and of course is handy when restoring an ART-13. The ART-13 used a pair of 811's (not 811A's) as modulators and an 813 as the final amplifier.
Collins Part Number 677-0002-00, designed in 1944 and last revision dated in 1954.
Power: 50 watts audio max. (Note: Hams have successfully used this transformer at power levels far exceeding (2-5 times) this rating.)
Audio Response:-2 dB @ 300 Hz, 0 dB @ 1000Hz, -2 dB @ 4000Hz
Terminals 1-3: 15000 Ohms, 4250v test voltage, current 150 mA balanced, (This is the primary).
Terminal 2: Center Tap.
Terminals 4-5: 7300 Ohms, 4250v test voltage, current 1-150 mA unbalanced, (This is the secondary).
Terminals 6-7: 970 Ohms, 2500 test voltage, current 2-10 mA unbalanced, (Used to modulate the screen of the 813 final).
19 January 1999