March 1936 Radio-Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles from Radio-Craft.
(Power supply protective resistor; calibrated dial; tone control.)
The chart at the left shows the locations of the tubes and their voltages, as measured to chassis. The usual high-resistance meter must be used. The bias on V4, of -23 V., is measured from chassis to the ungrounded filter choke terminal.
With the volume control set at maximum, attach the service oscillator between V1 grid cap and chassis, and adjust all I.F. trimmers for best signal. R.F. alignment is made at 1,400 kc., the adjustment being made on the trimmer located nearest the shaft end of the gang condenser.
The dial calibration may be corrected by tuning to a station of known frequency around the center of the dial and, while holding the knob so that it cannot turn, set the pointer to the correct position. The screw that controls the pointer is at the rear of the control head, and may be turned by an ordinary small screwdriver.
The special "globar" protective resistor across the secondary of the power transformer cannot be tested with an ordinary ohmmeter since it will have a resistance of several megohms when cold.
Posted July 13, 2015
Radio Service Data Sheets
These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers.