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DOCNUMBER 8410
Document Issue 1.1
August 2015
Page 2–5
RKR Designs LLC
Alpha 8410 Linear Amplifier User Manual
Amplifier Components and Specifications
Mains Board
Power-supply functions are split between the mains board and the HV
board. The mains board deals mostly 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 transformer primary.
Also on the mains board is a step-start circuit. This circuit consists of a
relay and a resistor, which are time-sequenced to limit the inrush current
into the amplifier when it is first turned on. When the amplifier is initially
turned on, the tap relays operate from a voltage derived from resistors
from the AC line. They hold via contacts on the trip relay on the HV
board. The regulated –12 and –124-V supplies are also located on this
board. Many of the important voltages for the amplifier are brought to test
points on this board.
The primary voltage taps are located on the top of the mains board,
between the transformer and the front panel.There is a row of five “fast-
on” connectors (J22 through J26) and a flying jumper connector that
mates with them.
T/R Board
The transmit/receive (T/R) board contains the RF input and RF output
relays as well as the input-power detection and output directional
wattmeter. Voltages from the detector are connected to the control board.
A trimmer capacitor on this board has been adjusted at the factory with
the amplifier operating into a good 50-ohm dummy load. This capacitor
should be adjusted only at the factory.
The board also has an 800-V protection device on the RF output.
Tube-Deck Board
The tube-deck board is located in the tube deck, below the tube sockets. It
contains critical circuit elements that need to be in close proximity to the
tubes. The tube heater, bias, and screen connections are all located on this
board. The tube-deck temperature sensor and the input match for the tubes
complete this board.
For more information on the tube deck, see
Section 2.4, “Tubes and Tube
Deck,” page 2–6
.
