User's Manual

ALPHA 9500 Interim OPERATING MANUAL
www.alpharadioproducts.com
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The amplifier is designed to use a single 8877 triode tube manufactured by CPI Eimac Company
of San Carlos, CA. The amplifier design uses this tube well within the published ratings. The tube
is operated in Class AB1, with a plate voltage of 3,300V (nominal, full output, key down), and a
cathode voltage of 9.4 V.
5.3 Output Tank Circuit
The output tank circuit of the Alpha 9500 is designed to provide reliable high efficiency, low
distortion performance in a very compact volume. The basic topology is “pi-L”, which provides
harmonic attenuation adequate to meet the requirements of all countries globally that permit
power outputs of 1,500 watts. Band switching is under automatic control and is accomplished
by a four-wafer band switch. These wafers are used as multi-function tap selectors, which
simultaneously select band taps on the inductors and include varying amounts of capacitance to
provide band-spread on the tune and load capacitors. The band switch wafers are in the RF tank
area. The band switch position is controlled by a stepper motor in the front sub chassis.
5.4 Tube Deck
The tube deck is a mechanical assembly housing the tube socket and the cathode (or input
match) PCB.
5.5 Power supply
The power supply has two major sections, a switchmode supply for the logic circuitry, and a
conventional transformer supply for all other voltages. When the amplifier is plugged in to the
ac line, the switchmode supply is always on. Thus, all the microprocessors are active. It is usual
for some of the front panel LEDs to “blink” momentarily when the unit is first plugged in. The
remaining voltages are produced by the HV and Mains Boards, described below.
5.5.1 Mains Board
The power supply functions are split between the mains board and the high voltage (HV)
board. The mains board mostly deals with the primary side of the transformer. The various taps
for the transformer primary are routed through this board and so is the AC line input. Relays
on the mains board connect the AC line to the appropriate taps on the primary. Each time
the On2 button is pressed the microprocessor on the mains board samples the line voltage
and determines which tap to select. That voltage tap will remain selected until the amplifier is
turned off, and will not change, even if the line voltage fluctuates. If you install your amplifier in a
location where the line voltage is not steady, you may force the tap selection via the serial or USB