Recovery technology

Padder Feedback

restore normal oscillator activityPadder feedback was/is a technique for boosting the action of the oscillator section of the frequency changer valve in Superheterodyne receivers. Some sets had it incorporated in the factory as in the 520M. It can also be added to existing circuits by the restorer to boost the effectiveness of a weak frequency changer valve -as these valves age, the oscillator grid current may fall to such a low level as to cause the oscillator to fail at some or all frequencies in the band. Returning the earthy end of the oscillator bypass capacitor (typically 0.05mf in later sets or 0.1mf in early superhets) to the hot end of the padder capacitor (typically an 450 pf mica capacitor in broadcast band sets using an IF of 455Khz) rather than connecting it to earth, will boost oscillator grid current sufficiently to restore normal oscillator activity and thus the frequency conversion necessary for superhet operation.

In the accompanying diagram, taken from the schematic of a battery set using a 1C7G frequency changer, the 0.1mf bypass capacitor is shown connected to the padding capacitor (PC). The original connection from B+ to ground is shown in dotted lines.
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