Copyright Donald W Thomas, K5ZRQ
7
4.1 INITIAL TUNE-UP
:
Read all of these tune-up instructions before turning the power on or attempting tune-up. It is very
important that the amplifier be properly tuned if it is to provide long life and good performance. Never
operate the amplifier if it is not properly tuned.
1. Set “DELAY” switch to the “AM” position.
2. Set “POWER” switch to the “LOW” position.
3. Set “PLATE” control to “5”.
4. Set “LOAD” control to “5”.
5. Place AC “POWER” switch in the “ON” position. The red pilot light should be on. Always allow at
least one minute warm-up before proceeding with tune-up or operation.
6. Key exciter (transceiver) in transmit mode (AM). If single sideband is the only mode available,
tune-up of the LA-600 can be accomplished by a sustained whistle into the microphone while
holding the push-to-talk button down. In the AM mode, it is only necessary to press the
push-to-talk button on the microphone (do not talk into the microphone in this mode). Either
method will provide the RF drive required for tuning the LA-600.
7. Quickly adjust “PLATE” control for maximum meter reading. There should be a definite maximum
meter reading and as the “PLATE” control is moved in either direction the reading should decrease.
8. Quickly adjust the “LOAD” control for maximum meter reading.
9. Steps #7 and #8 should be repeated several times until no greater reading can be obtained. Do
this as rapidly as possible.
10. Now switch RF “POWER” switch to “HIGH” and repeat Steps #7 and #8 several times until a
maximum reading is again obtained.
11. The “POWER” switch can now be used to select “LOW” or “HIGH” power output.
4.2 OPERATION AFTER TUNE-UP:
AM Operation: “DELAY” switch should be in the AM position. When the exciter (transceiver) is keyed
into the transmit mode, the LA-600 will automatically go into transmit. During AM
modulation a slight downward deflection may be noted on the meter. This is a normal
state and will not affect the audio quality of the transmitted signal.
SSB Operation: “DELAY” switch should be in the SSB position. If there is a long pause between
words during a transmission, the antenna switching relay in the LA-600 will return to
the receive position. Talking into the microphone will automatically return the
antenna switching relay to the transmit position. This relay action is normal.
