EF Johnson Audio Amp - RT's Radio Home Page

Go to content

Main menu:

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 Johnson sales pamphlet states it will work with other Johnson AM transmitters.  

I am investigating using it to drive the Viking 500 modulator.   The Viking 500 will remain stock, so modifying this amp for wider spectrum audio will be easy and easily reversible.

 






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




A plug for the rear jack was found thanks to 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.
Back to content | Back to main menu