GREEN-SCREEN TV


This is my construct of a design sited on cool386's website, namely:
This two inch set uses a 902-P1 cathode ray tube displaying pictures from a DVB-T receiver or other video source.
I have altered some things; as necessary to suit the components I have available to me
I have used a 3" PDA type CRT 3JP1, this needs 3 to 4Kv anode supply.
I used the cockcroft-walton voltage multiplier to obtain the necessary high voltages.
Original design featured valves with low filament current. I have substituted 6AU6 and 6CL6 types.
Instead of a valve based audio amp I have used an LM386 audio module.
A "work in progress"
Click on any photo's for a larger view.






Clamping circuits were common in analogue television recievers.
These sets have a DC restorer circuit, which returns the voltage of the signal during the back porch of the line blanking period to 0V.
Low frequency inteference, especially power line hum, induced onto the signal spoils the rendering of the image,
and in extreme cases causes the set to lose synchronization.
This inteference can be effectivley removed via this method.
From Basic Television, B. Grob 4th Ed © 1975

Timebase generators are ot the "phantastron" type design
AKA transitron-miller rundown circuit
Here is an explanation:




Dr F.P. Williams was a young wartime radar boffin.
He was well known for his birdsnest breadboard circuits which often left the board,
trailed across the bench, and over the edge.
He was also known to comment on circuits with "Oh! Very sanitary!" or "Phantastic!"
In those days, time bases and the delay of pulses tended to depend on
an exponential rundown due to the simple RC arrangements used.
He worked on linearising the rundown to improve stability, by using "Miller" feedback.
His pulse-stretching circuit using 2 pentodes + 2 diodes was named
the very sanitary Sanatron
and the single pentode version became the phantastic Phantastron.



This is a scan of an Australian magazine RTV&H Sept 1957
describing the handbuilt fabrication of a monochrome TV receiver
using a 5" dia electrostatic CRT.
Quite advanced for that time!