W4JKL's Glowbug Web Site


Mystery Amplifier

I found this amplifier at the Shelby, NC hamfest. It's a bit smaller than Collins S-line gear.

amp12.jpg (60K bytes)

The seller didn't know anything about it. But I was attracted by its beautiful workmanship and mechanical layout. It appears to be a conventional tetrode (4X250B) amp with (missing) regulator tubes for the screen and grid bias and a switch for selecting a tuned or passive input circuit. The only thing strange about it is the lack of a chimney for the tube cooling (note the big anode connector in the photo below). There is a muffin fan behind the tube, on the back panel. Controls are l-r bottom: grid tune, pilot light, band, power switch, meter switch, then in line above: plate current meter, tune, load, grid/screen meter.


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The octal sockets are for the plug-in electrolytic caps. I brought them up slowly with the variac and rectifier and they appear to have re-formed ok.

amp3.jpg (60K bytes)

The miniature sockets are for the regulator tubes (it appears). I've ordered some 0B2's to put in there. Stay tuned for the results. Note the switch, input resistor and input coil in the upper left. The HV is provided by the big transformer in the pictures and a voltage doubler circuit. The transformer appears to be ok, but the diodes in the doubler are shot and VERY hard to get to. I will substitute a perf board assembly for it and leave the original in place. The octal based caps are 80mF at 450V each, giving 20mF at 1800V for the array. I'm guessing I'll see 1500V to 1800V out of the supply.The strange cooling arrangement makes it hard to guess at the amp's capabilities.

Here are some additional photos of the amplifier.

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amp5.jpg (60K bytes)

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amp10.jpg (60K bytes)

amp13.jpg (60K bytes)

If you can identify this amplifier I'd like to hear from you!

Remember, with the voltages used in this equipment, it's Safety First!!