Swan Electronics Corporation - December 1968

Swan Service Bulletin #9B

Formerly, when switching to TUNE/CW position, the CAR. BAL. control was inoperative. With this modification, the CAR. BAL. is now operative. Thus, when tuning up it will now be necessary to also turn the CAR. BAL. control off from its null position in order to feed carrier through. Following the new tuning instructions will accomplish this.

Subject: 15 meter spurious radiation with 350 and 400 transceivers.

We have received a few reports of spurious radiation from 350 and 400 owners while operating in the lower portion of the 15 meter CW band. It will be reduced to an acceptable level by the following:

Disconnect the wire connecting pin 9 of the balanced modulator tube to the REC-TUNE CW switch. Cut at pin 9 and insulate or remove.

When this is accomplished, the tuning procedures must be revised as follows:


1. Turn the CAR. BAL. control clockwise until a slight increase in meter reading is obtained.

2. Rotate the PA GRID control for maximum meter reading.

3. Rotate the PA PLATE control for minimum meter reading.

4. Adjust CAR. BAL. for a reading of 150 ma.

5. Rotate the REC. TUNE switch to TUNE position. Quickly check the PA PLATE control for "dip" or minimum reading. If the meter dips to less than 500 ma., increase loading by rotating the PA LOAD controls clockwise. After each increase in PA LOAD, resonate the PA PLATE again; that is, adjust it for dip. Continue increasing PA LOAD until the PA PLATE dips to 450-500 ma. Then switch back to RECEIVE.

CAUTION: Do not hold the transceiver in TUNE position for more than 30 seconds at a time, even though PA PLATE is resonated. With full grid drive to the 6HF5 PA tubes, which you have in TUNE position, they are dissipating considerably more power than they do during normal voice transmission, so A SHORT TUNING PERIOD MUST BE OBSERVED.

6. Key mic and balance carrier out with CAR. BAL. control.

CW OPERATION - Special Note

1. Tune transmitter to full output; same as for SSB operation. Then adjust CAR. BAL. for a meter reading of approximately two-thirds the maximum tune-up reading. For example: if tune-up results in 400 ma cathode current, adjust CAR. BAL. for approximately 275 ma. OR, if tune-up reading is 500 ma., then reduce to approximately 350 ma. for CW. etc.

NOTE - This reduction in drive is essential on 15 meters in order to eliminate a possible spurious radiation. Full power input can be used on all other bands. (KD7VA NOTE: Always use carrier balance to control power output on CW. Extend tube life by using only as much power as necessary.)

2. Insert CW key in the Key Jack provided on the back of the 350. Use a standard 1/4 inch diameter 2 circuit phone jack.

3. Add a .47 or .5 mf 200 volt capacitor across the Key. This capacitor may be added internally to the 350 if desired.

4. Switch to TUNE-CW position to transmit. Back to RECEIVE for receiving.


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