Passively and Safely Neutralize the Ameritron AL-572 and Other Amplifiers

Please forgive the few audio warts.

In this video of an AL572 Ameritron amplifier, I show an amplifier that was grossly out of neutralization.

This cell phone video shows how to tell if an amplifier is out of neutralization. If adjusting the plate control (resonance) causes a large change in exciter SWR and a large change in exciter power level, the amplifier is out of neutralization. Improper neutralization will significantly impact fifteen-meter through ten-meter performance.

I designed the AL572 many years ago. The AL572 uses a manufactured coaxial capacitor to balance out the 572B anode to filament capacitance. The construction of this capacitor is critical. It must have a smooth rounded end #8AWG wire that extends to the stop depth of the blind hole in the Teflon insert. The Teflon insert must be correct. This capacitor can have over 3000 volts peak across it. The capacitor cannot have insulation flaws and the tubing and wire must be free of sharp edges.

The #8 AWG wire should be just over 3 inches long.

In this amplifier, MFJ-Ameritron cut the wire too short. It never should have left the factory this way because it is impossible to neutralize. The wire they used was only long enough to null two tubes.

I replaced the #8 with a smooth rounded end wire of the proper length. The amplifier performance radically improved on 15 through 10 meters.

This method works perfectly in the AL811H only if the two tubes nearest the butterfly capacitor flapper plates remain connected, or if only the flappers are bent in and out. The test setup also works on the AL1200 and other amplifiers.