View Of Pilot Light Socket And Canopy - RCA Radiola 17 Service Notes

(a) Place set in normal operation with loudspeaker connected.
(b) Remove Radiotrons 2 and 3, counting from left to right (first audio and detector stages facing
front of Radiola).
(c) Locate position of three potentiometers in power unit.
(d) Adjust potentiometer, located at extreme right when facing front of Radiola (Figure 13), for
position of minimum hum.
(e) Now replace Radiotron No. 2 (UX-226), previously removed, and
adjust the potentiometer located at the extreme left (facing the front of the Radiola) for position of
minimum hum.
(f) Replace Radiotron UY-227 and with the Radiotron in normal operation
adjust the center potentiometer for minimum hum.
Under normal conditions these three adjustments will suppress any noticeable hum in the
loudspeaker.
If the foregoing procedure does not reduce hum, try the following:
(a) In some cases when adjusting the potentiometers there may he no apparent point of minimum
hum. This is due to low line voltage and may be remedied by throwing the line switch to the position
that gives maximum brilliancy of the pilot lamp. If this does not remedy the trouble, try changing the
position of the line switch to each location several times. There may be a dirty contact in this switch,
making a high resistance connection which may cause the filaments to glow below normal brilliancy.
When this condition is present it will be impossible to adjust the potentiometers for minimum hum
until the filament
temperature of all Radiotrons is normal.
(b) When adjusting the UX-226 potentiometer (at the left) it may be noted that the position of
minimum hum is at one extreme of the potentiometer. When this is encountered the potentiometer
should be arbitrarily placed at its center position and then the UY-227 Radiotron placed in its socket
and the center potentiometer adjusted for minimum hum. The left potentiometer may now be re-ad-
Figure 14—Detailed view of the pilot light socket and canopy.
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