The AM Forum

Back in the very early 1970s, Radio Shack sold a very useful, inexpensive signal injector.  It was cylindrical, and I believe it was powered by either one or two "c" batteries.  At the front was a probe and either the back or side had a momentary push button to activate it.  It was basically shaped like a flashlight with a probe sticking out of it.  It produced a harmonic-rich square wave that was great for injecting a test signal into audio circuits as well as IF and HF RF circuits. 

There are times these days when such a handy, portable device would be useful in my electronic toolbox.

Does anyone know where I can obtain one of these?  A search on eBay and the internet has not proved successful.

It isn't finished, but here is the scan of the original instructions, a homebrew that someone made, and the schematic.

http://www.antiqueradios.com/forums/viewtopic.php?t=109446&highlight=

Simple device, you could probably pen tube it (My son's school has some MONSTER pens that are about 3/4 inch across, would be GREAT for HV probes and other such thing.  Waiting for the ink to dry up, and I get them BOTH!!! ).

Hope that helps.  I'm going to build one as well.. You're right, they are about indespensable.  That, and a signal tracer is a poor mans sig gen and scope!

--Shane

and from ebay:
http://cgi.ebay.com/AMPLIFIER-RADIO-SIGNAL-TRACER-INJECTOR-REPAIR-K7000-KIT_W0QQitemZ350245910227QQcmdZViewItemQQimsxZ20090829?IMSfp=TL090829183003r15977

I have one of these:
http://cgi.ebay.ch/SIGNAL-INJEKTOR-SE-250-C_W0QQitemZ220473109433QQcmdZViewItemQQptZRadio_TV_Musik?hash=item335538abb9&_trksid=p3286.c0.m114

Don't know who manufactured it though.

I think I have close to a million hours of running time on mine Eric. As I recall, back in the late 70's you told me they were on sale, might have been a close-out, and I grabbed one. It still works fine, runs on 2 AA's, and it's usually the first thing I grab when probing through audio stuff. I haven't seen anything else like it from any local retail stores, but the one Bob posted looks like the same idea. I'll trade you even for your Flex 5000!

Same one Radio Shack used to peddle I got one.

Check this one out.

http://www.qrpkits.com/tracerinjector.html

Bob
wb6kwt

Eric,

You want a Don Bosco Mosquito!!
A commercial pen sized AA operated unit. Neat.

It's basically a multivibrator, makes squarewaves, the harmonics go way up...

There was a great project in the old Popular Electronics that I built from the 60's I am trying to recall the name, it was a combo injector and tracer depending on if the earphone was plugged in or not. Maybe it was "tracex" not sure...  think so... look it up!

Today you could make it run a bit hotter since that was old low power germaniums... and there are small high power silicon devices today... two transistors, iirc... I built mine into an old styrene toothpaste case...

            _-_-bear

EDIT: I think the trick on the don bosco was that the output was coupled via an xfrmr, but the thing was wound with the coil on the outside, so that it would inductively couple into a circuit if you just held it close, and of course really dump something if you made contact with the probe... fyi.

I am pretty sure I have the tracex article squirreled away in one of my binders in the lab... maybe, think so. (it did not have the xfmr out though)