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EF Johnson Audio Amp

Amateur Radio > Vintage Transmitters
The E.F. Johnson, 250-33, is a 10 Watt audio amplifier intended to work with the Johnson Viking Kilowatt for AM operation when the Viking Pacemaker SSB transmitter is used as the exciter; a sales pamphlet also states it will work with other Johnson AM transmitters.   I had not heard of this device until I recently found this one.


The amplifier had not been touched in decades.  Like the Viking Valiant found elsewhere in this site, the power cord had rotted away leaving strings of copper wire and rubber crumbs.  New capacitors and resistors were installed as needed. A 1N4007 diode and additional electrolytic filter capacitor was installed downstream of the 6AL5 bias rectifier since this tube can impart hum from the AC filament.

Connecting through an audio output transformer to a 10 inch speaker, it produces very clean audio in the standard EF Johnson tone.

I found a plug for it thanks to the tips from users of the Antiqueradios.com forums.  

Rear view.
The schematic for the 250-33 Amplifer.  The audio string has some similarities to those of the Viking Valiant and Viking 500.
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