Tuning a Linear amplifier

Amplifiers, Peter Rodmell G3ZRS


New From: £29.95 GBP In Stock

First thing is first: Make sure you have a dummy load that will handle the amplifier running at full power!

Connect the dummy load to the amplifier via an antenna switch. Switch the amplifier power on. Read the plate voltage meter on the amplifier and make sure the voltage is within the limits specified in the amplifier manual. Then Power up the transceiver. Select the band and frequency you wish to operate on. Set the mode switch on SSB, and turn the transmitter drive control to the settings requested in the user manual for your linear amplifier. Set the amplifier bandswitch to the desired band, remembering that some amplifiers might not cover the WARC bands, however you can usually still tune them.

Set the “Load” control at approximately 25 per cent for 160, 80, 60 or 40 Meters, or 50 per cent for higher bands. Set the “Tune” or “Plate” control in the middle of the range indicated on the dial for the desired band. Set the amplifier meter to relative power. If your amp has the “CW/Tune – SSB” control to “CW/Tune,” you can use it here.

Tuning

*Transmitter can be keyed with a CW tone or with a whistle, many stations use the latter method.

  • Key the transmitter*, and advance the drive control until the relative power meter on the amplifier begins to move.
  • Adjust the Tune control for maximum indicated power.
  • Adjust the Load control for maximum indicated power. Switch the meter to grid current, and check that the reading is within the limits specified within the user manual.
  • Advance the transmitter drive control to full power. Readjusting the Load and Tune controls for maximum output power as required. Observe the plate amperes meter and check that it does not exceed the maximum value specified in the manual. Release the key.
  • Switch from the dummy load to a resonant antenna for the band in operation. Key the amplifier and re-peak the Tune and Load controls. Select the desired operating mode on the transceiver.

Incorrect tuning shortens the life of the tubes dramatically! Remember also that if you require an ATU with your antenna system this needs to be rated at a PEP greater than your amplifier output!

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