Wireless World 1964 Oscilloscope

[djrm]

I have acquired this old home made Wireless World Oscilloscope, built from a design published in 1964. There are a few minor faults on it bit unfortunately the tube has a big fault - it is really dim and will not focus. In desperation to find the cause of the problem I replaced the 5 inch VCR97 with a pin compatible 3 inch tube and it seems to work. There is no uMetal screen on the replacement - the pattern shown is is all due to the magnetic field from the various transformers, the amplifiers are disabled by having their valves removed..

I don't know what has happened to the tube, maybee the focus connections is disconnected inside. The base is loose on the neck so perhaps a wire has broken although I cant see it. Could it be gassy? there is still a dim spot about 2cm across. There is almost 2kV eht, I cant turn it up any more.

I used to have a few old 5 inch CRTs, but they all got lost in various house moves and over drastic clear outs, now I dont have one, shame. I'd like to restore it to working condition. The design is interesting in that the Y amplifier and timebase are plug-in modules. It reminds me of the 'scopes I had - one of which I made myself from an old radar display.

           

Another unusual feature for a home-made design is the RF-EHT unit, in all there are approx 16 valves, three transformers, and some semiconductor rectifier and other diodes. I received the schematic with most of the changes the constructor made from the published design. It must have took some building, he said it took months with all the metal folding involved.

[Ed_Dinning]

Hi, I remember building a version of that scope many years ago; I believe I used a rectangular tube of better quality bought from the Edgeware Rd. This scope was I believe, claimed to have a 20Mhz bandwidth

From memory the VCR97 was available with different connections. In some units 3 anodes were brought out to one pin, in others they were brought out to separate pins. This allowed the use of a separate Astig control.
It could of course just be a gassy tube.

Let me know how you get on, I may even have a spare tube here

Cheers, Ed

[djrm]

Greetings Ed, 
I see from the construction articles it was designed to have a better quality tube. 

Once back in the 70's I embarked on building a later WW 'scope after having found a good quality twin gun tube in the local surplus shop. I built some amplifiers and a timebase but unfortunately suffered an accident one day when the main power supply got dumped across the heaters and that was the end of the tube. I kept the circuits for a while but never found another tube.

Yes this one could be gassy. I don't know how to tell for sure. I shall look tonight when it's dark in the shed to check if I can see any pink glow inside the tube. Its mainly working I've seen a trace and Y amp sensitivity so its almost there. 

Kind regards, David.

[Ed_Dinning]

Hi David, from memory the A2 is the focus electrode. Try a wider range of voltage on that and see what happens. Not sure if you will actually detect gassyness by a pink glow.
If I still have the rectangular tube (also twin beam I think) then you can have it. I mat still have some of the switches, HV caps etc about that you are welcome to

Cheers, Ed

[djrm]

Thanks for the kind offer Ed. I think I'd rather stick with a VCR97 than modifying it to take another kind of tube altogether. I don't really fancy building an old fashioned 'scope, just having it working for posterity or something.

I have tried changing the focus resistor chain to no avail, it was because of this I put the old 3 inch tube it to see what was happening. I all comes in nicely with that one - apart from the magnetic interference as noted. You can see a fine trace on my first photo.

My next scope will be a much faster beast for looking at digital circuits, none of the old ones are any use for that.

I'll go back to reading about all those strange hoarders now ...

[peter scott]

Hi David,

I have some 5" VCR97 or possibly 517s and you are welcome to one. That said, I'm in Edinburgh and would not like to post one. Perhaps you could arrange a forum transport.

Peter.

[djrm]

Hi Peter,
Thanks, I'm not familiar with the 517 and had to look it up.
I found these useful tables detailing the various old CRTs: https://frank.pocnet.net/other/docs/CRT-data.pdf
Is the 517 one of the blue with yellow afterglow types. I used to have one. The blue image was very sharp, much better than the VCR97 I had at the same time.
I would be happy with any and am in no great hurry.
Since I do not leave the county very often a forum relay transport would be very useful for me if it could get one nearer to my home in North Yorkshire.
Kind regards, David

[ppppenguin]

According to this data sheet: http://www.r-type.org/pdfs/cv1517.pdf the '517 was available with several different phosphors. Confirmed here: https://www.radiomuseum.org/tubes/tube_vcr517.html This data sheet gives the different phosphor types: http://www.r-type.org/pdfs/cv1517.pdf but I'm not familiar with any of them.

I've not tried any of them, but I've heard that the blue flash with yellow afterglow (P7) gives good results for TV if a suitable blue filter is fitted to block the yellow. Otherwise it will be horrible as soon as anything moves. More about phosphors here: https://en.wikipedia.org/wiki/Phosphor

[djrm]

Thanks for that additional information Jeffrey.
I did a little research about phosphors recently when I bought a blue phosphor VCR138 type tube, I was hoping to find an orange one.

Many years ago when I was at school I built a flying spot slide scanner based on a design I found in an old hobby construction book. it used a 5 inch tube with a P7 phosphor and filter read by a 931 photomultiplier. That kind of gear was available from the local surplus store near where I lived back then.

The scanner never worked too well, it was a bit too complicated for me at the time but just about managed to work. I used the old discarded family TV as display monitor. I wish I still had the book describing it, I think it was one of the Newnes series popular at the time but could be something else.

Picture shows the blue and green tubes I found recently, no long persistence extra phosphor on this blue one.

Kind regards, David.

   

[ppppenguin]

The phosphor requirements for professional flying spot scanners are stringent. You need the shortest possible persistence to minimise the need for afterglow correction. You also need fine grain. Not too bad in monochrome where short persistence blue is readily available. Harder for colour where you need enough output across the spectrum to give decent signal to noise ratio. Ideally with the same short persistence across the spectrum.

The decay curve of a phosphor is not a simple exponential. From memory I think the afterglow correctors in a Cintel Mk II scanner had 5 or 6 separate adjustments, each with a different time constant. Replicate this for each of the RGB channels. There was a special slide or film to set them up correctly.