Hawes Mechanical Television Archive by James T. Hawes, AA9DT

Animation: Mechanical TV receiver with magnifier

Build a Mechanical TV Monitor, Part 1

Block diagram of mechanical TV receiver

Simple display driver for mechanical television. Between 1928 and 1931, a video amplifier consisted of three tubes. (See 1928 schematic.) I wanted to accomplish the same function with three transistors. Better still, two of the transistors would be in one Darlington package. After I tinkered in the shop for a few days, the project worked!

My circuit provides the entire video electronics and the video display for a mechanical television receiver. See the block diagram above. Build my circuit, and you'll have the equivalent of diagram blocks 2, 3 and 4.

SPECS

  • My display consists of four series strings of three LEDs each.

  • A high-gain, PNP preamplifier provides a substantial voltage boost.

  • A Darlington power transistor drives the display.

  • The circuit is entirely direct coupled. (Direct coupling is necessary to avoid phase shift, especially since I don't clamp the DC.)

  • Total circuit current is in the neighborhood of 160 mA.

  • Each LED string handles 40 mA peaks.

  • The circuit input source is a CD containing narrowband video. The NBTVA sells such CDs to club members. See the sidebar for a link to the NBTVA.

  • With this amplifier, a "Walkman" type CD player can drive the display. To reconstruct the picture, scan the display with a Nipkow disc.

  • The gadget works like a champ. The contrast range is broad, and the pictures should be acceptable.

  • As with the 1928 Daven circuit that inspired my design, picture sync is up to you. This circuit has no effect on sync.

Daven mechanical television (mechanisches fernsehen) preamp & lamp driver

My inspiration: 1928 video amp and driver by Daven.

Click... Explanation of mechanical TV block diagram





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