Labels:text | diagram | black and white OCR: CONSTRUCTION The Blue Box uses the tones per digit. We p+9v + 7. PUSHBUTTON show one oscillator and a common amplifier, hoth being turned on when the pushbutton sinds .W thru the diodes. one for c.ich of the two oscillatorstfor that buttons Jigit1 47X and one for the amplifier, 3h diodes are ISK used, or an on-off switch on the amp Iets yes use only Eltmatched siliconl, The best speaker is a telephone earpiece. Each tone mixes thia a I7k resistor. 3Pk sets gain. Entire current drain under 10 ailliamps. 74 SIov Oscillator Frequency . 1/2x3. 14xRxC, when chie 3 1/2 R + V TELE PHONE R/2 pot is dliusted to the point of oscil- FARPIECE LAA Mation. This point has no distortion, and the frequency can be raised, but distortion ONE OSCILLATORS 47K Gets mu. For 1500 cycles, and C .0022, R= 7 NEEDED ...
