Here's a nifty two tube code practice oscillator. Based on 1950 plans. Grab a 35Z5 and a 12SQ7 and whip one up in an evening. Just follow the schematic below, and note a couple construction notes below the schematic. Mostly junk box parts, too!

About the most important thing to note is that this is based on old AC/DC radio style circuits, where ONE SIDE OF THE AC IN GOES DIRECTLY TO THE CHASSIS! PLEASE MAKE SURE IT'S THE GROUND SIDE THAT GOES TO THE CHASSIS. AND REMEMBER THE CHASSIS CAN BE HOT! Most of the parts are not critical values. For construction I just used a project box from a different project, mounted jacks, power and pots in holes that were already there, mounted the two tube sockets, added 3 terminal strips inside for convenient places to connect things, followed the schematic and soldered it together. Of course originally designed for hi impedence headphones of the olden days (we're talking bakelite with metal diaphrams) it will work with more modern 'phones plugged into it. Now at least when you're practicing your code you'll see the glow of the tube and feel like a code operator should there're back in the olden days of ham radio (tee hee).

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