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SERVICE NOTES
of good radio schools conducting correspondence courses in advanced radio — ■ just what the serviceman needs.
Knowing what one is doing is extremely important in this fast-moving radio art. All the test equipment in the world will not tell what's wrong with a radio set unless one knows how to use it. And much more than a superficial knowledge is required to do a job quickly and eificiently so as to show a profit.
A few minutes a day studying the basic radio principles, if not already understood, and the new developments will repay the servicemen by saving many hours in repairing sets. While it is essential to have adequate modern servicing equipment, a thorough technical knowledge of radio is even more important.
STEWART-WARNER R-1 83 CHASSIS
* The 11-183 chassis is employed in receiver models 1831 to 1839. Set is a superhet with an R.F. stage operating on all bands. Circuit shows receiver with wave switch in BC position.
Antenna wave-switch makes connections for doublet antenna on short wave band. Note iron-core antenna coil for BC band.
I.F. and R.F. section of set are of usual design. Reactance dimmer type of tuning indicator. Second section of diode used in delayed AVC circuit. Fixed bias from the power supply is used with the 6L6 beam power output tube.
Trimmer locations and frequencies are shown on bottom view of the chassis. Alignment procedure is standard.
CROSLEY 1117
* This years Crosley 11-tube chassis is a 2-gang superhet tuning 3 bands. Set designed for use with a doublet antenna or ordinary type. Wavetraps are used on models shipped to locations where I.F. interference may be prevalent. (Circuit on p. 34.)
A two-stage I.F. amplifiei is used. One stage of this I.F. uses resistance coupling. Separate triodes connected as diodes are employed for detection and AVC.
Fixed bias is used on the 2nd I.F. amplifier, the 1st audio stage and to provide a delay on the AVC circuit.
Phase inversion is obtained in the
output stage by using a load resistor in the screen lead of one of the 6K6G tubes. In Series 1 resistors are used in the screens of both output tubes; Series 1 also differs from Series 2 in that a .0001 condenser is connected from the grid of the 2nd I.F. tube to the wave switch — shown in dotted lines.
Chassis layout shows the trimmer locations and proper frequencies.
PHILCO 38-4 & 38-5
* The 1938 Philco models 4 and .5 have almost identical chassis. The 38-4 has a cone-centric automatic tuning system, while the 38-5 has a standard dial with *a shadow tuning meter. (Circuit on page 34.)
Set tunes on BC band and shortwaves. Separate R.F. coils are used, wired in series — shorting switch shunts BC coil for shortwave reception. A tuned R.F. amplifier is employed on both bands.
Antenna coil is of low impedance type for use with Philco all-wave antenna system.
The suppressor grid of the I.F. amplifier is coupled back through a tertiary winding in the first I.F. trans(To page 36)
STEWART-WARNER 1831 TO 1839
Chassis R-183
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