RACAL RA-237B Gerry O’Hara
4
switch);
-Several discrepancies were noted between the schematic and S/N179:
o A 0.01uF capacitor (C61) is included in the schematic between the anode of the RF
stage and the 1MHz LP filter (absent in Serial No. 179). This change is interpreted as a protection of
the 1MHz BP filter inductors in the event of a capacitor failure in the filter sections;
o A 1pF ceramic capacitor is included in the schematic between the two sections of the
2MHz bandpass filter after the harmonic generator (absent in Serial No. 179). This change is
interpreted as improving the characteristics of the bandpass filter;
o A 47kohm damping resistor is included in the schematic across the primary of the
2MHZ bandpass filter after the harmonic generator (absent in Serial No. 179). This change is
interpreted as providing an improved tuning characteristic of the 2MHz BP filter primary.
- The above changes were incorporated into the rebuild.
Also noted that errors in manual text relating to tube pin-outs – those in the balanced mixer.
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