Trying to make a vision IF and Detector - fun!

[AdrianPH]

If you search ebay for this item number 264675809338 this is the small unit I use when doing my development playing! It will do 6.3 at approx 3 amps and 250 Volts at 25mA before it starts to drop output.

I tend to think it a bit safer than using transformers when i have my fingers close to the copper clad work. It will still hurt and discharging a cap charged at 250 Volts is still the same if off mains or not, but it's a feeling.

I do not have a variac unfortunately or a regulated HT power supply, these little units regulate quite well for what they are. I do have a few of them, one powers the time base section I have already build and a second powering this Vision IF, at the end of it all I would switch over to a transformer PSU I built in the early stages of my TT15 audio amp, it will do 250 Volts at approx 80 to 100 mA so that would be the final idea. I do need to change it over to a valve rectifier rather than the silicon diodes I have in there at present.

It will be a few days before the valves turn up, some time to come up with a temp solution.

Adrian

[AdrianPH]

The tuner valves and some other parts arrived and tried with some success. The Buck HT power supply can not cope with the extra load of the tuner so the output Volts dropped to around 180 Volts from just over 200, so it all had a low supply, but I was able to use it with the IF strip to demodulate the video signal, giving me around 8 Volts peak to peak from the detector. I also added a few more components to give A.G.C. volts and that would show a typical value of -4 Volts going back to the tuner. So I no longer need to use the 9 volt battery idea.

Also in the post was a GZ34, so planning on building a general valved PSU on to a chassis to supply the unit and also provide HT for the CRT at a later stage.

Adrian

The detector is neagative going to the

[Murphyv310]

Hi.
Try these https://www.ebay.co.uk/itm/DC-DC-10-32V-...2343801842

Youll get 100ma regulated from 12v DC, a lot safer than using those Chinese mains operated ones.
Then you can make it portable too!!!

[AdrianPH]

I have two of them, not what I would say are quiet from the rf and noise situation, and only regulates when under a load at better than say 7 to 10mA, otherwise they tend to bob up and down a bit, well mine do anyway.  I do use them on my basic valve tester.

I have been working on this in the afternoon/evening:-
   

I took down it's previous incarnation using semiconductors and changed over to a GZ34, basically as the transformer has a 5 Volt winding and 4 amps at 6.3 Volts.

The hardware, holes and fixing now down and I will wire it up tomorrow and check regulation.  A bit more leathal than a 12 Volt buck but what I would need towards the end of it all.

There is a good chance it will still have semiconductor diodes used on it to provide a negative supply via a voltage doubler so I can drive the CRT with around 900 Volts.  I left space on the top there for fitting it later.

Adrian

[Murphyv310]

Great progress.
Nice chassis, I've found locally that getting an engineering shop to supply aluminium and make up chassis's, dress and weld the corners to be unbelievably expensive, this has put me off finishing many projects due to costs.
I don't have room for a folding press, I even had to sell off my compressor due to the lack of space.
I'm certainly watching this thread with interest.

[AdrianPH]

I guess I am lucky in that I can do many small scale things myself. I have always been interested in building 'stuff' in metal, cannot do the small model gear as can not see a practical interest in it so build a few simple karts ending up with a road legal car a Haynes Roadster.
So in the workshop I have milling machines, lathe, welder, plasma cutter etc. Everything tends to be desk top size including a small press from a car jack and can form small lengths with that.
The chassis is 1.5mm steel which is simpler to weld and grind smooth and it is easy to hide things with a coat of primer and silver paint. Down side is a bit heavier.

I made three chassis for the TT-15 audio amp I did, in fact I made four, this being the first of the four which I bent up in the wrong direction so ended up as a different size. But a case of waste not. Problem is it is getting to be cold in the garage now.

I will get the PSU wired and tested today hopefully.

Adrian

[AdrianPH]

OK some progress, wired up the power supply and tested it under various conditions to see how it performs.  It was from the UKVRRR forum so no proper specs.
   

I am tending to run the boards at 230 Volts DC and each board so far HT wise is taking:-

Vision IF   24.5 mA.  Timebase 26 mA.  Tuner  24.3 mA
So need to get a series resistor to drop some Volt.   The 6.3 V heaters draw is now at 3.3 Amps.

Now no laughing at this woodwork, but I need to keep things together, so tuner Vision IF and Timebase boards at least held together for now.
   

Adrian

[AdrianPH]

A bit of progress, not much, but some.  I have to decide on which CRT method of doing video modulation I am going to use, cathode or grid?

So I am going to put down my thoughts here as a way of getting feedback, and basically trying to get it correct in my grey matter.

WRT Volts, the grid is negative to the cathode, so positive going video (-sync) will brighten the screen on video peaks.  Negative going video (+sync) applied to the cathode will brighten the screen on negative peaks.  At this point I am working on using the grid for video input and varying the cathode to provide fixed brightness.

Not knowing how much voltage swing I need from black to white I am making an assumption of 50 Volts maximum. 

The plan using a DG7-5 CRT is to have the final anode at +HT of 230 Volts, which means that the cathode is down at around -600 Volts, this as it is relatively easy to use a voltage doubler from the mains transformer secondary to provide this negative volts using the normal HT to provide the 800 to 900 Volts required for the tube.  It also means that the deflection plates are within the normal HT range approx 200 Volts.  The down side is a separate 6.3 Volt heater winding for the CRT.

I have issues which I am not getting through, one is DC restoration of the video as it has to be in the -600 Volt area, the second frame flyback suppression, using the screen grid from the frame miller timebase as a blanking pulse to drive the CRT grid when that is the video input?

Anyway this is the circuit diagram to date.


  personnalTV.pdf (Size: 90.25 KB / Downloads: 2)

Adrian

Also on UKVRRR

[ppppenguin]

Tradionally, electrostatic CRTs were run with the cathode at negative EHT. This allows the deflection plates to be directly coupled to the X and Y amps in a 'scope. In a TV you have an alternative - run the cathode at low voltage and AC couple to deflection plates at +ve EHT. Some pre-war TVs did it this way. It may well be easier than AC coupling the video and DC restoring it.

[Geordie McBoyne]

The tuner is the Philips AT7650 and was fitted many UK made TVs including the Philips "Style 70" series of 1965. Other manufactures used it and as mentioned in an earlier post the KB Featherlight, also in the KB VC4 series.

Geordie McBoyne.