The following RF amplifier turning procedure is only a recommendation. Follow it at your own risk. Reference your RF amplifier's owner's manual for their recommendations.
Connections:
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Connect 50 ohm coax between transceiver RF output to the amplifier RF input
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Connect 50 ohm coax between amplifier RF output to an Antenna or Dummy Load
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Connect your transceiver DIN/RCA PTT and ALC outputs to your amplifier's PTT and ALC inputs (note: ALC optional)
Tuning Procedure:
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Set both the "LOADING" and "TUNE" air variables on the RF amplifier to 50% (mid reading)
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Set your transceiver to about 20 watt carrier output
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Key your transceiver in CW or RTTY mode with the amplifier turned off
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Validate you have a 1:1 match to the load. If you have an antenna tuner in-line, adjust your antenna tuner so you have a 1:1 match to the load
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Unkey your transceiver
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Power on the RF amplifier
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Key both your transceiver and RF amplifier
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Watching the Ip (Plate Current) meter on the RF amplifier, rotate the "TUNE" air variable to the right or left, until you see a dip in Ip reading. You can also watch your RF output meter for maximum power out. When Ip dips, RF out should peak
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Now slowly turn up the RF drive level from your transceiver, 30, 40, 50……….90 watts out
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While you are turning up the transceiver RF out power, keep adjusting the "TUNE" air variable on the RF amplifier for Ip dip (RF out peak)
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Un-key the transceiver
Once you reach ~100 watts output from your transceiver, its time to adjust the "LOADING" air variable on the RF amplifier
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Reduce the transceiver's output to about 50-60 watts drive
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Key the transceiver and amplifier
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Adjust the "LOADING" air variable to right or left about 40/60% on the scale. I don’t know which way, you may need to try both directions. If you get less RF output, move the "LOADING" adjustment the opposite direction.
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Adjust "TUNE" again for Ip dip (RF max out)
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Turn up the transceiver's output drive to 90-100 watts, You should have more RF output
Additional Comments:
You will need to do this over and over and over and over, again and again and again, until you find the sweet spot where you no longer get any additional RF output out of the amplifier. You will need to do this for each band and frequency. Once you find the sweet spots for each band and frequency, write them down as present numbers.
You should also watch the Ig (Grid Current) meter. If Ig goes to high you could damage the tubes. Adjusting the LOADING air variable will alter the Ig reading. A good rule is don’t drive the tubes greater than 50% Ig on the meter and you should be OK. If Ig gets higher then 60-70% on the Ig meter, you could damage the tubes. For a pair of 3-500Z tubes, normal Ig is about 220 ma. Consult your owner's manual for maximum Ig.
If you hear arcing across the air variables, this means the amplifier is out of resonance. Reduce drive and LOADING so the amplifier is putting out less power and you have a good Ip dip with TUNE. Then increase power input and adjust amplifier LOADING.
You may also want to only key your RF amplifier for durations no longer then one minute. Then let the amplifier cool off for 2-3 minutes before keying again. Depending upon the amplifier, if its out-of-resonance, tuning for longer durations could stress the components and tubes.
You will need to find the sweet spot for each band and frequency where the RF amplifier is resonate. The important thing, start with 20 watts drive and find the spot, then turn up the power, adjust LOADING and find the spots where you have max RF power output.
Once the RF amplifier is correctly tuned, glass tubes will have a nice reddish-orange glow to the plates.
