Screen Modulate Your Globe Chief: Poptronics

[WA4WAX]

See page 68.  Tow tubes, and away you go!!

http://www.americanradiohistory.com/Archive-Poptronics/60s/61/Pop-1961-03.pdf

[W2JBL]

I had a Globe Cheap a while back and built a modulator on the chassis using a 6L6, and found the rig worked very well screen modulated. Timtron has it now I think. Anyway the grounded grid 12AT7 input stage shown is useful for more than a carbon mic. I used it for the first stage in the modulator I built for my most recent ARC-5 setup, but modified. I put a 1K resistor from the cathode of the first stage to ground, and a 47MF coupling cap from the cathode end to the mic input. It makes a wonderful high level (-10 to 0 DBM) input impervious to RF. For the carbon mic bias I used the output of a 7808 regulator IC through a 680 ohm resistor to the carbon (or amplified dynamic in my case) mic. The IC is powered by rectified filament voltage or DC filament voltage from the car's battery source. A toggle switch disables  the mic bias for line audio. If I jam a T-17 carbon mic into it it's instant "bandits at twelve o'clock" audio.