How to tune an amplifier

Optimizing the performance of a HF amp for each operating frequency and antenna combination is important. Proper tuning causes the amplifier to be more ‘fuel efficient’. Tuning for maximum output, so long as the tube’s specifications are not compromised, usually coincides closely with ‘highest efficiency’. This condition results in less heat dissapation from the tube and other circuits. A maximum output condition usually coincides with a reduction of Harmonic levels and Intermodulation Products.

The Alpha 77 and most other amateur band amplifiers generally exhibit sharper tuning on bands above forty meters so forty or eighty is a good place to start practicing. The tuning on 160 is so broad it’s hard to get a handle on the personality of the unit.

With the tune-up cheat sheet handy, set the bandswitch to the proper frequency range and set the Tune and Load controls by the chart. Monitor grid current continuously if you have an external wattmeter. If you need the Alpha wattmeter, switch back and forth. Sweep the exciter’s power control upward while making a carrier. The transceiver’s output should be allowed to go no higher than 100 watts. Adjust the Load control back forth to see if you can make the power output go a little higher. Observe the grid current as you make the same moves and you’ll likely see a decrease in grid current along with a slight increase in output. Next rock the Tune control and you should see a peak in the grid current and a very slight peak in power output. If the grid current didn’t go up much, you’re done. If the grid current peaked significantly higher, lower the grid current using the Load control.

Try to keep the grid current below half scale. Quick excursions to near full scale are unavoidable during tuning. "Go there but don’t stay long."

Lower the drive, if necessary and re-optimize. Some operators prefer keying the radio with a stream of dits while tuning. This method cuts the duty cycle in half, resembling speech patterns.

It is a good idea to write down your ‘SSB and CW’ settings for each band. Or if you operate more than one antenna per band it is likely the settings will vary slightly from one antenna to another.

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