Specifications

Radio Alpha Products Inc. ® Alpha 99

POWER: overdrive and flattopping. A switch-selected bargraph

monitors three additional functions:

TUNE: Permits a simple and safe tune-up procedure to be

performed at low output power. See section Tune-up

below.

IP: Plate current, 1.5 amperes full scale (approximately 75 mA

per segment).

HV: Plate voltage, 3000 VDC full scale (150 V per segment).

Tune-up

The objective of tune-up is to adjust the amplifier (and the drive applied to it) to obtain

optimum efficiency and linearity at the desired output power. Any linear amplifier

must be adjusted for optimum efficiency and linearity at each specific power level. If

operation at higher power is then attempted without appropriate readjustment, the

result will be flattopping, “splatter,” and (usually) excessive amplifier grid current. If

operated at a much lower power level than it has been adjusted for, the amplifier’s

efficiency decreases considerably.

Grid Current

The ALPHA 99 operates in Class AB2 when delivering maximum output power

consistent with excellent linearity. A small amount of grid current flows and the green

GRID MIN LED lights as drive approaches the optimum level. The green GRID

LED will flicker on SSB voice peaks, and light under CW/SSTV/RTTY carrier

conditions.

As overdrive approaches, grid current increases rapidly and the red GRID MAX LED

lights. At maximum output and efficiency, the red LED lights dimly; full illumination

of the red LED indicates overdrive and must be avoided. If the red LED lights before

the desired value of plate current and/or power output is reached, readjust amplifier

loading before continuing.

On SSB, optimum output consistent with good linearity occurs when the green GRID

LED lights on most voice peaks and the red LED flickers dimly only on the highest

peaks.

Excessive grid current results from overdrive and/or inadequate loading. The solution

is to reduce drive, and/or increase amplifier loading. The 99’s 4CX800A/GU74b

tubes are well protected and these adjustments tend to be less critical than in many