WD2XSH/31
Forrest, Virginia, USA
Brian Justin,WA1ZMS
QSL TO:
Brian Justin, WA1ZMS 1704 COTTONTOWN ROAD FOREST, VA 24551-3910 USA
Homebrew 1920 MOPA (Master Oscillator, Power Amplifier) rig that would have been vintage in the early days of real 600m amateur operation.
(See "Radio Telephony for Amateurs" by Ballentine page 124.)
Click here for .pdf of the above
Hand keyed CW with a 1917 Clapp-Eastham straight key.
The rig is running a couple of watts into a Marconi-T antenna feed against ground.
Engraved brass tags for the front panel will be added.
Oscillator is UV-201 and final is UV-202
Power supply built with all vintage parts (except for modern
bleeder resistors! Original design didn't have any back in 1920.
Present operating position. A 1920's Grebe CR-8 receiver
will be used with the MOPA transmitter for 500 KHz operating.
XYL helping drive ground extra rods near base or Rohn 25 tower
with VHF antennas. All grounds are now tied to common point.
Have to adjust that filament voltage to keep the 1920
UV-202 running and not burn it out.
Ladder line feeing 160m dipole as the hat of the Marconi
T antenna. After improved grounding, antenna feed resistance
is now 19ohms. About 15 of that is
still due to ground loss.
Top shelf: MOPA Exciter Middle shelf: Variac in metal box next to "Power supply of death!" <--- as my wife calls it. (But it's only 700VDC) Third shelf: Hafler 9505 amp with balun box on top of it Right of that is W1VD style LPF then Bird wattmeter. Tuner not shown is across the room on the operating desk. Also quite shown is 12" fan behind Hafler amp to keep it cool. Hafler 9505 draws 450w at 120v when idle, and climbs to 1.5kW when key down. Makes a nice space heater in the shack for the winter months.
Close-up of MOPA rig shows nice new Poplar wood cabinet. Finish is Danish Oil stain, 2 coats of shellac, and 5 coats of hand rubbed wax. Bronze ring peep-hole is typical of 1920's tube rigs to make sure op can see and easily adjust brightness of tube filament.
160m dipole at 70ft high with 4 inch ladder line feed going to switch box and balun and loading coil on side of house. Switch box allows me to switch open wire feed to HF 4:1 current balun in grey box. Can fast switch from 600m to HF with open contact relay in small grey box.
Long white tube is 4:1 current balun for 600m. Large white tube is PVC 600m loading coil. #8 copper wire runs down side of brickwork to network of ground wires and 8ft ground rods to keep worms & grubs from freezing! Hi...hi...
