Swan Electronics Corporation

Service Bulletin #10: February 1967

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On units (350's and 400's) produced prior to June 1966, a few cases of low loading on one or two bands was caused by overheating of L-306 RF choke. Replacement of the RF choke, in such cases, restored normal operation.

On these models, medium voltage is present on the plates of the rear section of the PA (variable) grid capacitor when the unit is operated on 80 and 40 meters. Foreign particles between these plates can cause a momentary DC short to ground which results in overheating of L-306 (This is the green body RF choke in screen circuit of 6GK6 driver tube). This condition can be corrected by installing a .002 mfd disc ceramic capacitor in series with the lead to the rear section of the PA grid capacitor. Leads of the .002 capacitor should be cut short and soldered close to the tab of the PA grid cap.

TEN METER LOADING

Drive can be increased on the 10 meter band by re-peaking the PA grid control for maximum cathode current while the unit is in the "tune" position.

FINAL AMPLIFIER TUBE - Replacement

When replacing the 6HF5 final amplifier tubes in the Swan 350 or 400, it is recommended that GE tubes be used. It has been our experience that some of the other brands are extremely difficult to neutralize.

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(this bulletin was re-typed by David Byrd - KD7VA)