Signal injector pens

Over on the test equipment section of the Antique Radio Forum (ARF), there has been an interesting and long-running thread on signal injector pens like the Don Bosco Mosquito.


All the electronics nerds wanted one of these in their pocket protector. (Thanks to Steven Johnson for the scan of the Don Bosco brochure.)

Another ARF thread, mostly by Philip Colston, shows more examples of similar hand-held signal injectors.

With these threads in mind, I stumbled across a Gernsback Library book published in 1953 entitled Radio and TV Test Instruments, over on Pete Millett's excellent site. 


It has a chapter written by Robert E. Altomare on how to build the Signal Launcher, a hand-held vacuum-tube signal injector that is possibly the prototype of all of the pen-style electronic signal injectors. (Philip Colston pointed out that the electromechanical buzzer pen-style signal injector was introduced in December 1940.)

signal laucher schematic large

The Signal Launcher uses a 3A5 dual triode tube in a classic multivibrator circuit.


Robert E. Altomare was quite creative in packaging the circuit.

gernsback test signal-launcher

The image above links to a PDF file containing the excerpted chapter.

© Steve Byan 2011-2019