8
8.2 Mains transformer
The transformer is the heart of the amplifier, a high performance type, designed to reduce the size and weight. It is built with a
generous reserve of power, handling easily the DX-2 requirements in continuous operation. The primary can be wired for 200VAC,
220VAC, 230VAC or 240VAC operation. See Figure 2. There are several secondary windings, as follows:
Filament supply
Low voltage supply to the controller board
QSK module supply
Bias supply
Screen grid supply
High voltage supply
8.3 H. V. Power Supply
A full wave bridge rectifier and filter converts the high voltage AC into high voltage DC with a huge reserve capacity of 58
microfarads.
8.4 Soft start module
At power up, the mains power is gradually applied to the transformer by the soft start module. The power is gradually applied over a
time of about 5 seconds, avoiding the high inrush current typical for such big loads.
8.5 Sensor module
A small metal box positioned at the output of the DX-2. It detects the forward and reverse power, for measurement and display, as well
as for SWR monitoring and to activate the protection, when needed.
8.6 Antenna relay / QSK module
In the standard DX-2, the antenna relay is controlled by the transceiver, via the control board. It switches the antenna between the
transceiver, during reception, and amplifier, during transmission. It is also used to bypass the RF from the transceiver, directly into the
antenna, when the amplifier is in standby mode, or during special conditions like overdrive, bad SWR or other error conditions.
When the QSK option is installed, this is a module with two very fast, high power vacuum relays, and the control circuitry. The
purpose of QSK is to allow very fast switching between transmit and receive, during digital communications. See Annex 1 showing
oscilloscope displays of fast switching times and contact bounce-free operation of the QSK module.
8.7 Display board
This board has a number of inputs where various voltages are connected. The board converts these voltages into a "moving LED" type
of display. Two of these displays have flashing light indication (Ig2 and plate current).
8.8 Controller board
The brain of the amplifier is the Controller Board. The following circuitry is part of this board:
Bias voltage regulator, also incorporating a sensitive grid current detector for overdrive detection . Adjustable pre-bias,
removes the distortion at the beginning of the word, when EBS is activated.
Screen voltage regulator, with adjustable voltage and adjustable current limiting, for tube protection.
Overdrive protection and timer - based on detecting grid current, it initially gives visual warning and, at higher level of
overdrive, it cuts off the amplifier for 2 seconds. It ensures a clean signal, making it virtually impossible to overdrive the DX-
2
SWR detector and timer - switches the amplifier to bypass mode for about 3 seconds when high SWR is detected.
Adjustable SWR level. Factory adjusted to about 2.6: 1
EBS - the Electronic Bias Switch - senses the presence of RF input power and turns on the bias to start transmission.
Factory adjusted for about 0.5W. When the input power exceeds this limit, the plate current starts flowing. When there is no
speech, even for a very short time, the tube dissipation is cut to a low value, as set by the pre-bias adjustment.
Interlocking, timer for filament warm-up
Relay control: ready relay, SWR relay, over-drive relay, antenna relay
QSK switching control
Display control: Ig2 measurement and display, SWR cut-off display, overdrive warning display, READY display, FAULT
display
Logic circuitry, low voltage supply to the various electronic circuits
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