VCR97 Project

[Ed_Dinning]

Hi Gridrod, yes I made one and I knew of at least 2 others They were a bit fiddley to set up and I think there were a few corrections and updates given.
If you have access to old copies of WW I think there was quite a correspondence going, so there were quite a few builders.

Ed

[Radio Wrangler]

I was building oscilloscopes in the 1960s, at first with a 5BP1 tube and then a VCR97

One trick of mine was to cut the bottom out of a plastic flower pot and line the inside with sticky-backed foam draught excluder. The CRT then went in, with its neck through the bottom end hole, and the conical glass nestling in the foam. A bit of tension from the rear end held the tube securely. The aluminium front panel had a big hole and the outer step of the top rim of the flower pot sat on the edge of the hole.

It worked well and was very neat. A bit of matt black paint sprayed on the flower pot before final assembly completed the job.

The rest of the scope's design was rather constrained by me buying a tea-chest full of used CV138/EF91 from Jim Fish ( 50 bob if I remember right)


David

[FERNSEH]

I'm gathering up the components for my electrostatic CRT TV receiver. My next door neighbough gave a old phonograph cabinet which I intend to build in a pre-broadcast style of TV set for 120 and 180 lines. The kind of set that would have been made in 1933 to 1935.
I have an ACR13 CRT which similar as the VCR97, although I'm really on the look out for a 9 inch ES tube. If a 9" ES tube can't be found, then the ACR13 will have to do. The CRT will be mounted vertical and the picture viewed on a mirror in the cabinet lid. The ACR13 is 16 inches long. It's too long to fit in the cabinet horizontally for direct viewing. Anyway, a vertical CRT is more in keeping with this type of receiver.
The EHT will be in the order of 3 to 4 KV so the timebases will have to supply a swing of +500 to -500. The 1937 Wireless World TV receiver has the best timebase design employing two thyratrons and four high voltage triodes.
Suitable valves are the Mazda T31 or MO GTC1 thyratrons and Mazda AC/P4 triodes.
The timebase and power supply can be assembled on a 14 X 14 chassis which will be fitted on the cabinet floor.
The vision and sound receivers will be separate units which was the practise of those times. These will be positioned high up in the cabinet. I have still not decided on the valves for the receivers, although American types like the 6D6 RF pentode and type 76 triode could be considered. Many early sets were superhets. The RCA 1932 field trial receiver and the RR359 are my inspiration for the project. Both these sets have magnetic deflection CRTs though.
Many home construct VCR97 receivers employ the 6SN7 twin triode for the tube deflection plates drivers. This valve was not available in the early 30s, but a predecessor tube, the 6A6 was and it is still easy to find. It's good for 300 volts on the plate but I'd reckon one could get away with higher than that in a push-pull timebase.
Meantime, I've plenty other jobs and projects to do and I'm still looking for bits and pieces for the receiver.

DFWB.

[julie_m]

Originally Posted by grindrod

My Father built one for the Coronation using military surplus parts from Bob Potts in Derby

His shop's still going strong

[FERNSEH]

Found in a 1934 Practical Mechanics magazine a picture and some comment about a CRT receiver. No mention what type of CRT was employed. Most likely it was an electrostatic tube.
That loudspeaker escutcheon looks familiar.

DFWB.

[jhalphen]

Hi David,

Have a look at Roger Dupouy's reproduction of a US 1938 receiver:

http://la-radiovision.fr/ then scroll down (left column) to topic "US Cathodique 1938"

Also interesting is another receiver "Cathodique 180 lignes".

If you're interested in seeing the schematics drop a line to Roger via the Contact form on the site.

Best Regards

jhalphen
Paris/France

[Anthony Thomas]

Originally Posted by FERNSEH

Here's another electostatic CRT TV construction project. It appeared in the November 1952 PTV magazine.

Here is a thumbnail of my 3" television that this Practical television article describes. I built this about 30 years ago.

I will not power it up because it has been inactive for so long that many capacitors will need replacing. The power supply transformers are in the chassis on the right.

Tony

[Ed_Dinning]

Hi Tony, someone on the forum will have a copy of the article if you want it.

Ed

[Anthony Thomas]

I have the original Practical Television magazine, the FJ Camm book Practical Television Circuits so I am fine on that front Ed

Just need some motivation

[Anthony Thomas]

Just recently I started to look through my bits and pieces with the idea of perhaps completing one of my half hearted television projects from years past that have been collecting dust. I will be needing quite a few potentiometers that can take the wattage in those bleeder circuits in the crt stage, some are even marked 2W.

I will also need capacitors too but I was thinking of sourcing new parts there if possible, new or used parts I will hav eto test for their capacitance and leakage voltages.
Must get started on listing up what I do in fact need. I noticed that bases for VCR97 cost over £20 + postage, strewth...

Has anyone got started on any home built televisons recently?

Regards Tony

[brianc]

Hi Tony
The wattage rating for the pots in a CRT bleeder chain has no import as the current through them is tiny. The important thing is insulation and the larger diameter pots are better in respect of insulation between contacts but please remember that the shift and focus pots must be mounted on an insulating panel which is isolated from the chassis- and put decent sized knobs on them to prevent shock!
If you want a VCR97 socket, I can give a used one to you foc. My friend works in Bergen every other month (he is there at the moment) and can bring one over in March to post in Norway (if you can wait that long!). Otherwise, PM me with the postal details and I'll post it to you.

[Anthony Thomas]

Thankyou kindly Brian, I have sent a pm to you regarding the vcr97 socket, March will do fine by me

Thanks also for the advice regarding insulation of the pots in the CRT bleeder chain, I have some short insulator extentions from discarded Tandberg televisions that I will probably use.

I also intend using a sheet of Lexan to mount the whole group of pots for the CRT bleeder chain and centering pots and this should keep things reasonably safe, these high voltages are not to be toyed with.

Thanks again
Tony

[Radio Wrangler]

I would mount the pots back inside the unit and use good quality insulated shaft extensions.

I certainly wouldn't trust a knob for insulation at kilovolts if the pot insulation fail.

David

[Anthony Thomas]

I agree with you David, but those extentions I am talking about are made for television use on Tandbergs and Radionette. I am seriously thinking of long extentions like you suggest and the knobs used will be without steel grubscrews on all pots carrying high voltages.

Again, thanks for your concern David.

Tony

[Radio Wrangler]

I was just thinking that I would be able to hear the scream from here in Scotland.

As yet, I don't know any rude words in Norwegian.

David

[Ed_Dinning]

Hi gents, standard trick for pots with hv on them was to mount them on paxolin far back on the chassis and use Perspex rod as extenders, no problem with knobs and grubs crews then.

Ed

[Anthony Thomas]

I found this article on the Argus especialy helpful despite me having the book Practical Television Circuits by FJ Camm but just at the moment my copy has gone "awol"

Argus article: http://www.radiocraft.co.uk/agus.htm

There is however a very helpful update in this article which mentions a series of mods that I would like to include into my build.

It is here: http://www.radiocraft.co.uk/argus/mods.htm

I was wondering if anyone has done any of these updates as they all sound very realistic in both their execution and reasoning.

My question:

The Timbase; there is a modification mentioned, :"Revised sync separator from Nov '53 issue"
Does anyone have a copy or circuit diagram of this modification from Nov '53 by any chance?

I have over a dozen VR65 valves (tubes) for the Timebase and suitable sockets, I also have a CV2810 which might even be new. so I plan to use these parts if possible. I do also have several 6AC7 which I believe might even be better than the VR65 devices and they are normal "Int Octal" bases to boot I don't envisage trouble obtaining those BY206 diodes but anyway I do have those EA50s if needs be

Glad for any input from those that have built this project.

Tony

[Anthony Thomas]

Hope that it is OK to bump this thread to keep it from being closed, still collecting parts as and when

Tony

[Panrock]

Originally Posted by Anthony Thomas

The Timbase; there is a modification mentioned, :"Revised sync separator from Nov '53 issue"
Does anyone have a copy or circuit diagram of this modification from Nov '53 by any chance?

Thanks to Jon Evans, this circuit has now been added to the Argus site.

Meanwhile, I've now discovered my CV2810 tube was OK after all, and have finished converting my Argus to display 120, 180, and 240 lines. Count the lines here!

Steve

[Ed_Dinning]

Hi Tony, PM me with your shortages and I may be able to help.

Ed