Atwater Kent Mfg. Co.

Model 20
#7570
#4640

CONDENSERS
Detector phone .002 mfd #8241 500 volts
Detector grid .000250 mfd #4465 500 volts
Plate bypass .3 mfd #14902 450 volts

RESISTORS
Grid suppressors 600 ohms #4949 wire wound
Detector grid leak 2 megs #15892 1 watt Green
R-f rheostat 10 ohms #4690
Detector rheostat 10 ohms #4690

TRANSFORMERS
1st a-f primary 1700 ohms #4779
1st a-f secondary 3250 ohms
2nd a-f primary 1700 ohms #4779
2nd a-f secondary 3250 ohms

Model 20 #4640

The parts used in #4640 are substantiallyvthe same as used in #7570 shown above, with the following exceptions.

1st and 2nd a-f transformers have different part numbers. In #4640 they are #7661. The d-c resistance of the respective primary and secondary windings is the same as designated for Model 20 #7570. In other words a-f transformers #4779 and #7661 have like d-c resistance specifications for the primary and secondary windings. In receiver #4640, transformer #7661 is used in both the 1st and 2nd stages.

The detector grid condenser in receiver Model 20 #4640 has the some capacity and voltage rating as used in #7570, but has a different part number. The part number of this unit in receiver #4640 is #8112.

In both receivers, the plate circuit bypass condenser is adjacent to the 2nd r-f stage socket. The grid and phone condensers are adjacent to the detector and a-f assembly.

The wiring diagram in the manual shows a .2 mfd condenser as the plate circuit bypass unit. The Atwater-Kent specifications in their diagram manual shows such a condenser. On the other hand the parts specifications show a .3 mfd condenser in this position. If a .2 mfd unit is being used and the receiver performs well, there is no occasion for a change.