RCA-Victor Model 15U, Radio-Phonograph
Radio Service Data Sheet
April 1938 Radio-Craft

April 1938 Radio-Craft

April 1938 Radio-Craft Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

RCA-Victor Model 15U, Radio-Phonograph (radiomuseum.org) - RF CafeThis Radio Service Data Sheet for the RCA-Victor Model 15U, which appeared in the April 1938 issue of Radio-Craft, is the first 3-page instance I remember seeing in all the vintage electronics magazines. The Model 15U is a fairly sophisticated outfit, but not that much more so than some other pieces. There is a nice example of the Model 15U on the RadioMuseum.org website (thumbnail at left). It appears to be fairly clean, but not yet fully restored. A lot of adjustments needed to be made during the alignment of both the radio (commercial broadcast and shortwave bands) and the turntable. The electronics repair shops probably really loved this type of equipment since it likely needed frequent tending to if the owner gave it a lot of use.

RCA-Victor Model 15U, Radio-Phonograph Radio Service Data Sheet

RCA-Victor Model 15U (sheet 3), Radio-Phonograph, April 1938 Radio-Craft - RF CafeThese cores change the inductance of the particular coils in which they are inserted to provide exact alignment. All of these adjustments are accurately made during manufacture and should remain in proper alignment unless affected by abnormal conditions of climate or purported alterations for servicing, or unless altered by other means. Loss of sensitivity improper tone quality and poor selectivity are the usual indications of improper alignment. Such conditions will usually exist simultaneously. Correct performance of this receiver can only be obtained when these adjustments have been made by a skilled service engineer with the use of adequate and reliable test equipment.

Two methods of alignment may be used; one requires use of the cathode-ray oscilloscope and the other requires a voltmeter or glow-type indicator. The cathode-ray alignment method is advantageous in that the indication provided is in the form of a wave-image which represents the resonance characteristics of the circuit being tuned. This method is preferred because of the I.F. characteristics of· these receivers.

"Ultra Short Wave" Band (b) Connect the "Ant." output of the test oscillator to the antenna terminal "A1" of the receiver through a 300-ohm resistor. Set the receiver range selector to its "Ultra short­wave" position and its dial pointer to 57,000 kc. Adjust the test oscillator to 19,000 kc. The 3rd harmonic of 19,000 kc. is used for this adjustment.

RCA-Victor Model 15U (sheet 2), Radio-Phonograph, April 1938 Radio-Craft - RF CafeAdjust oscillator air-trimmer C23 for maximum (peak) output. Two positions, each producing maximum output, may be found. The position of minimum capacity {plunger near out) should be used. This places the receiver heterodyne oscillator 460 kc. higher in frequency than the incoming signal. Tighten lock-nut. Adjust the 'detector air-trimmer C3, while slightly rocking the gang tuning condenser back and forth through the signal, for maximum (peak) output. Two peaks may be found on this trimmer. The peak of maximum capacity (plunger near in) should be used. Tighten lock-nut. Adjust the antenna air-trimmer C10 for maximum (peak) output while slightly rocking the gang tuning condenser back and forth through the signal. Two peaks may be found on this trimmer which produce maximum output

"Medium Wave" Band

(e) Place receiver range selector to its "Medium wave" position with its dial pointer set to 6,000 kc, Tune the test oscillator to 6,000 kc. Adjust oscillator air-trimmer C14 to produce maximum (peak) output as shown by the waves on the oscilloscope. Two peaks may be found with this circuit. The peak with minimum capacity (plunger near out) should be used. Tighten lock-nut. Adjust the detector air-trimmer C36 for maximum (peak) output while slightly rocking the gang tuning condenser back and forth through the signal. Two peaks may be. found with this circuit. The peak with maximum capacity (plunger near in) should be used. Tighten lock-nut. Adjust antenna nit-trimmer C4 to produce maximum (peak) output. Tighten lock-nut.

RCA-Victor Model 15U (sheet 1), Radio-Phonograph, April 1938 Radio-Craft - RF Cafe"Standard Broadcast" Band

(f) Remove the 300-ohm resistor from between the test-oscillator "Ant." post and receiver antenna terminal and insert a 200-mmf. condenser in its place. Place receiver range selector to "Standard broadcast" position with receiver dial pointer set to 600 kc, Time the test oscillator to 600 kc. Adjust oscillator magnetite core screw L9 (top of large oscillator coil can) for maximum (peak) output as shown by the waves on the oscilloscope screen.

(g) Set receiver dial pointer to 1,500 kc. Tune test oscillator to 1,500 kc. (l,500-3,100-kc. range) and increase its output to produce a registration on the oscilloscope screen. Carefully adjust the oscillator detector, and antenna air-trimmers C16, C37, respectively, to produce maximum (peak) output as shown by the waves.

 

 

Posted July 21, 2017

 

 

 

 

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. There are 219 Radio Service Data Sheets as of November 15, 2017.