250-watt Transmitter Project

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Larry writes:   "I picked up a HB 1/4 KW AM/CW transmitter over in California about 3 weeks back.  Runs a 4-250 modulated by 100THs.  Real nice looking rig and well built, nothing tinny about this thing.  It has provisions so that I can use it strictly as an AMP and bypass all the other stuff if need be.  Working to get it ready for service as some of the electrolytics below the mod deck etc are losing their innards so need replacing,  next fall when it cools off more than likely."

"The wire bundles are unlaced because I had to trace out each and every wire between chassis's.  It was also wired for remote control which I have to figure out and then disable so I can run it from the front with provided switches.  Built-in antenna tuner for open wire or can bypass it to go straight to coax or can switch in a built in dummy load.  Looks pretty heave duty.  Will warm up the garage nicely this winter."

The rack panels, from top to bottom, are:
(1) balanced-line tuner, (2) metering panel, (3) final RF deck, (4) modulator and monitoring oscilloscope, (5) RF exciter and multiplier/driver stages (6) low-voltage power supplies and regulators, (7) high-voltage power supply and primary-power control.

Rear view of the top of the tranmitter rack.  The topmost unit is the balanced-line tuner, and immediately below it is the metering panel.  The bottom chassis is the RF deck.  The plate cap of the 4-250 can be seen to the right while the left-hand side is taken up by the plate-tank components.

Rear view of the lower part of the transmitter.  The 100TH modulator tubes are in the upper right, immediately in front of the modulation transformer.  The  odd-looking assemblage on the left side of the modulator deck is the built-in oscilloscope for waveform monitoring.  Below the mod. deck are chassis containing the RF exciter/multiplier stages and  various low-voltage power supplies.  The high-voltage supply is built into the bottom of the rack.

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