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The biggest piece of equipment here is a 50 year-old tank-circuit
amplifier built around an Illumitronics coil by [or for] Art, W1KK.
Art was a ham from across town, although mostly active long before
my time. I bought this amplifier at a club tailgate, and have used
it ever since. There are four 811A's inside, and the power is
supplied by a 1500V rack-mounted power supply that weighs close to
75lbs. You can find more information on this amplifier from the
June 1961 QST: "A Compact High Power Linear" by Floyd K. Peck,
K6SNO. Though this amplifier presents a good deal of work and adds a few steps for an operator, it is clean and electrically quiet. The usual question given the competitive nature of the sport is the comparison to newer, more commercial amplifiers. The answer is no; in fact this amplifier has a quicker move than the Henry 7K and runs at around the same temperature as any Ameritron that has been in here. This is a piece of gear that must be flown with silk gloves, but is just as solid and reliable as it was back in its day.
The above photo shows the front of the amplifier. Clockwise from upper left: drive, band switch, capacitance, plate, and grid. You can just see the power supply to the left. The amplifier is a fairly standard pi-network tank circuit with a 500W coil. The QSK is via the extra relay in the back of the radio (in the case of the TS-440, the acc port). The interesting thing about this amplifier is that it operates at zero bias. A relay puts 100V negative bias from the radio to cut off current on the plate while in stand-by. This is the oldest amplifier I've owned to use this method. Tuning "fats" takes a good deal of time, so the written pre-sets are important. Proper loading can take almost ten minutes otherwise. We can run a full kW across 15-80, thanks to the beefier power supply. Obviously, there are no grid warnings, so I wired a light to turn on when the mA across the grid was higher than normal.
The picture above above shows the rear of the amp. Keying lines, power, and the RF in/out coax are all there. The "T" on the output is for a coaxial reject stub (one side goes to the stub, the other to the switch matrix). As of May 2009, we have burnt out five 811A's, broken 2 rectifier tubes, and replaced the coil once. We got around to performing a thorough cleaning in 2008, which increased the tuning efficiency. The next project will be to replace the band switch, adding a sturdier tap for 15m. I would also like to build a duct to vent the cabinet to open air.
The current tubes are by General Electric and are the originals. I found a matching spare which I cycle around on a 6-month basis. Why cycle? A tube that sits for a long period without being used slowly allows air back in. This is why when hams key up with an old "backup" tube, it usually is bust. The other reason for cycling the tubes is that I have yet to find a reason not to. |
