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Old 11th Jul 2010, 2:56 pm   #41
FERNSEH
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Default Re: VCR97 Project

Hi Trevor,
I understand that you are operating your set with a positive EHT system. No problem with that. I just means that the shift pots will have to be fitted on a paxolin panel and the control shafts will have to made out of some insulating material.
Some circuit designers favour negative EHT which means that the brightness control is a 2000volts.
The project is progressing well.

DFWB.
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Old 11th Jul 2010, 3:16 pm   #42
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Default Re: VCR97 Project

Hi Sean,
Here are some copies of the PTV article of the Personal TV project.

I hope the pictures are clear enough, if not I'll redo them.

DFWB.
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Old 11th Jul 2010, 4:45 pm   #43
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Default Re: VCR97 Project

Hi.
I have made up the HT section using modern 500v 47uf snap in caps 2 IN5408 rectifiers with series surge limiter resistors, I have temporarily fitted an RS smoothing choke but it's a little too low in rating for the full set with RF audio and the likes so will be replaced when I can find a better one (there is one in the loft somewhere) As David correctly says the shift pots need to taken off the chassis so I have fitted them onto a temporary paxolin board above the tube mount, I will get some modern high insulated types at a later date, I have also mounted a two valve bases for the line osc and drive for which I am using an EF50 & a 6SN7GT, I have wired up the heaters but I think that will be all for today.
You will see a 220k resistor floating on the HT line, this is to discharge the smoothing as a pre-caution. I've already had 300v on my tongue today
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Old 11th Jul 2010, 9:46 pm   #44
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No I couldn't resist it! I had another hour this evening, I have wired up the line osc and drive valves, all I need to do in those stages is to relocate the width, line hold & line linearity controls to the side of the chassis, this will reduce the cable lengths to the controls as they are presently mounted at the rear of the chassis, with a little luck I will have line scan either tomorrow night or Tuesday.
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Old 12th Jul 2010, 4:51 pm   #45
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Default Re: VCR97 Project

Hi Trevor, just back from hols and I've seen this thread.I have a compendium of PTV and other circuits on this type of set. One was even available that used the 1CP1 (1") tube, some magnifier needed there!
Let me know if you need any more information. I built several of these sets as a young lad nas most of the VCR97's had electrodes strapped together (A1, A3 and int coating from memory). Some, however, had them brought out seperately so you coud then use an astig control that sharpened the picture up no end.
I have a good collection of EF50's if you want to be authentic when you build the RF stages and I can probably find the insulated pots for the CRT chain if you need them.

Ed
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Old 13th Jul 2010, 10:55 pm   #46
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Default Re: VCR97 Project

A pre-war GEC TV set model BT9121 employed a 12" electrostatic CRT.
The CRT operated with a final anode voltage of +6KV. This means that the shift controls operate at 6KV as well.
The pictures show the controls are fitted on a ebonite panel and the control shafts have insulation parts.
The timebases are of an unusual design. A thyratron, type GT1C operates as the oscillator which in turn drives a triode connected KT66. The anode of the KT66 drives a special transformer which has two balanced secondary windings. The secondary windings are at EHT potential. This is a circuit I would not recommend to anyone.

DFWB.
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Old 14th Jul 2010, 7:40 am   #47
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Default Re: VCR97 Project

Hi David.
That sure is a very odd circuit, something that I have seen on pre-war equipment in the past is very strange circuitary, no doubt designers were at liberty to try anything at the time!
I haven't proceeded with the project over the last two days for a couple of reasons, the first and most important is that Anne is not well and secondly I need a couple of pots.
Will do more at the weekend.
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Old 14th Jul 2010, 9:14 pm   #48
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Default Re: VCR97 Project

Hi.
I have now mounted the lline hold & width controls on thw side of the chassis and wired them up, I then tested the oscillator but got nothing. I had decided to use an EF50 but this valve and half a dozen of it's brothers would not work either, after checking and re-checking I got the books out and the calculator and after some calcs came to the conclusion the EF50 was a bad choice. I did have a couple of EF55 (video amp valve) and on paper looked OK. I popped one in and hay presto. All I need to do to the line stage now is to fit 2 caps and a pot for line lin and that section is complete.
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Old 15th Jul 2010, 8:22 pm   #49
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Default Re: VCR97 Project

Hi
In between giving oldticktock some technical advice I have wired up the 6SN7 temporarily and connected up the "line" plates with the following result, both the speed and width controls operate correctly. I'll tidy my work and build the Frame stages at the weekend.
I have made numerous changes to the original circuit and feel the overall result will be very good.
So far so good.
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Old 15th Jul 2010, 8:56 pm   #50
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Default Re: VCR97 Project

Great result Trevor. Well done.
Your making fast progress. Its good to see something on screen so soon.
Looking forward to seeing the field time base working too.

Frank
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Old 17th Jul 2010, 10:04 pm   #51
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Default Re: VCR97 Project

Hello.
Having taken stock of parts I need tonight, I will need to get some more pots to do the frame timebase and drives. It will be next week before I can complete the frame stages, so keep your eyes peeled.
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Old 19th Jul 2010, 7:37 am   #52
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Default Re: VCR97 Project

Hi.
I have managed to find the required value of pots, so last evening I fitted the valve bases for the frame timebase and also the sync seperator, I also drilled a couple of holes for wiring requirements and marked off where the pots for the frame will need to go.
I may get a little time during the week to do some more but I have jobs in Inverness & Aberdeen this week so I need to see how things pan out.
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Old 26th Jul 2010, 7:16 pm   #53
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Default Re: VCR97 Project

Hi.
Due to my redundancy I won't be able to carry on with the project at the moment. I need to get organised in working out what I am going to do. At the moment I think I will be repairing pressure washers on a self employed basis.
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Old 26th Jul 2010, 7:55 pm   #54
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Default Re: VCR97 Project

Trevor,

If there is anything you need for this project, let me know - I have a fair heap of bits here that might be of use.

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Old 26th Jul 2010, 8:04 pm   #55
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Sean.
Many thanks for the offer, do you have in your junk box some spare time? My problem now is too start earning again.
I will certainly let you know if I need anything.
Thanks Sean.
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Old 26th Jul 2010, 8:06 pm   #56
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Default Re: VCR97 Project

Sadly my pile of "round tuits" have gone, but other parts are quite abundant.

Would say the earning problem will be a short one, given your progress on this project!
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Old 4th Jan 2013, 9:44 pm   #57
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Default Re: VCR97 Project

Quote:
Originally Posted by FERNSEH View Post
Here's another electostatic CRT TV construction project. It appeared in the November 1952 PTV magazine. It uses a 3" 3BP1 CRT but it should be possible to adapt it for the VCR97. The timebase valves are EF91s. The RF stage uses two EF95/6AK5 pentodes in a cascode arrangement.
I hope that no one is against me resurecting this thread? I at last became a member here earlier today and it was due to articles like this one mainly.

I have this particular Practical Television magazine from the early 1950s together with Practical Television Circuits by FJ Camm. This particular televisor was one that I partly constructed at the beginning of the 1980s from The Practical Television Circuits book. Mine isn't a true copy but quite close.

My tinkering with home built televisions was due entirely to this book and at one stage I did try to obtain a 62 indicator unit to build the £9 television, this was in about 1967 when I used to live in Brighton.

A few years ago I was fortunate in obtaining an apparantly new CV2810 CRT from the UK, a base was obtained at the same time. I have 12 new Maxda octal valve bases from J Birkett and 2 holders for the EA50 diodes. The components are collecting and the chassis shouldn't be a great hindrance to duplicate, just need some inspiration and a suitable shove to get started.

There have been several helpful suggestions further up in this thread.

Anyone wish to PM with me?

Thanks, Tony.
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Old 4th Jan 2013, 11:30 pm   #58
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Default Re: VCR97 Project

Here's a quick video of mine.

http://youtu.be/5LBMcZ6dNC4

Quite frankly it's currently shelved , along with most of my workshop as I'm trying to move house.
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Old 5th Jan 2013, 7:49 pm   #59
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Default Re: VCR97 Project

Hi Tony, I built some of these sets when they were first published in the mid 50's. My mother complained about the green colour, but would not stop watching it!

I probably have some suitable parts and further circuits. PM me if you need additional info.

Ed
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Old 5th Jan 2013, 8:44 pm   #60
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Default Re: VCR97 Project

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

I have a chassis with the remains of the Slow Scan TV receiver I built as a teenager 40 years ago that I could adapt as an interesting project! It has a 7BP7 tube with a home made focus coil, the deflection yoke was from an old 405 line TV that I broke up. EHT is from a 2.5kV transformer with a voltage doubler. The deflection amps were Sinclair audio power ICs, they look like 16 pin DIL packs with a finned heatsink attached, they would be no good for high res TV!!

I will drag it out of the loft and dust it off!!

Does anyone remember the Wireless World colour TV project of the mid 70's? I wonder if anyone made one?
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