Specifications

13
Figure 3: TRANSFORMER AC INPUT CONNECTIONS
8 DX-3 DESCRIPTION
8.1 RF Section
The RF section occupies the right hand side of the DX-3 (looking from the top - front). See picture in 1.1.
RF Switch and tuned circuits
At the front of the amplifier are two variable capacitors, for plate and load tuning. A 9-position ceramic
switch is employed for the 9 operating bands. Next to the switch is the 40 to 160 metre tank coil. The silver
plated, large diameter copper tube is the 10 to 30 metre tank coil.
RF Sub-chassis
The GU78B tube is positioned on a separate RF sub-chassis. All the connections to the tube, except for the
plate, are under this sub-chassis. A 9-way heavy duty connector is used for the outside connections. The fan
blows air into this sub-chassis, which is forced out through the ventilation fins of the tube. A second fan
above the tube helps by sucking the air out. The air temperature is sensed by 2 sensors placed above the tube
(they can be seen between the fins of the top fan). The sensors must stay in a position close to horizontal.
Make sure you are not pushing them down, too close to the tube, as high voltage exists between them.
240
230 220
0
200V:
200
FAN
240
230 220
200
0
220
220V:
FAN
240
220
200
0
230
230V:
FAN
240
230220
2000
240
0
240V:
FAN