[Boatanchors] FW: FS: EF Johnson 250-39 Electronic T-R Switch

Mike Langner mlangner at swcp.com
Thu Jun 30 12:08:58 EDT 2016

Subject: [Boatanchors] FS: EF Johnson 250-39 Electronic T-R Switch

This little unit that Bob has is a really useful item for boatanchor users.
I have two of them, one hooked up to my Viking Valiant, the other is a spare
for the moment.

A perfect use for these little guys is full break-in cw -- before I got the
Valiant I used a Gonset GSB-100 with a Hammarlund HXL-One amplifier and the
TR switch -- again, worked great.

And yes they have a little gain.  You can make yours have more gain by
increasing the number of turns in the secondary of the little ferrite core
"receiver output transformer" inside the unit.

The little units do make a surprising amount of heat, which is why Johnson
put them in TVI-proofing metal housing with lots and lots of holes for air

And using the 6BL7 is important -- there are "same base pinout substitute
tubes" that're easier to find, but the voltage rating(s) of the 6BL7 mandate
it for use with high power.

Whomever has a use for it and gets it should be well please.  I'm extremely
pleased with mine !


Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901

(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner at swcp.com

More information about the Boatanchors mailing list