Build a Mechanical TV Monitor, Part 1

	Build a Mechanical TV Monitor, Part 1

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.