for some years i have a dream about to build my own B/W monitor (from the start i want to build a television) but i dont want the tuner and IF, so far i have a schematic to build from, it is from a old Danish television from 1961, it will have 6 tubes, i have earlier make som tests on TV and put the composit signal from videosource directly to G1 on the video tube (often Pcl84 or Pl83), it have a isolation transformer between the TV and powerplug.
A friend of me is electronic engineer ,and the told me that a videomonitor needs a "videoshaper" circuit for more stable picture, so my question is, can anybody comfirm that? and does anyone have some schematic to a tube broadcast video monitor? im curious about how its build up
Alex 🙂
Hi Alex,
to build a good quality video monitor you will need to satisfy several requirements the average TV set does not. So, taking them in turn:
1. A flat frequency response in the video amplifier to beyond the system bandwidth in question, with good group delay characteristics. It must not be influenced by the capacity of the CRT cathode.
2. Stabilised EHT, so changes in beam current do not affect the size of the picture, which leads to
3. Stabilised scans, and very importantly
4. A proper black level video clamp that actually clamps the signal to video black level, not the sync tips. The video is normally clamped during the back porch of the video signal and you'll need to avoid clamping on the burst (often a small choke is inserted to remove it).
Elektrotanya has the service manual for an old stalwart we used for many years at work, the Melford DU1. You may wish to download and study it.
Hi.
I know the basics about clambing, black level ect. but im just curious about how other build monitors like Philips EL5749(based on tubes NOT transistors) i want to keep it simple,
does anyone have some schematic to a tube broadcast video monitor? im curious about how its build up
If you look in the library under "Broadcast Monitors" you will find the circuit diagram for the monochrome PYE 2780 broadcast quality monitor. Its 405 only but is all valve and might give you some of the insights you are looking for.
Here's a thing I made a few years ago. It's not up to much tbh, but it was an interesting project for a while...
https://andydoz.blogspot.com/2014/09/simple-tv-using-dg7-32-scope-tube.html
Hi .
Thanks for the tip to the schematic, i have studied for a while now, its very interesting, i think you know the schematic so is it okay if i asked for some question to it?
regards
Alex
