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Old 2nd Nov 2020, 2:23 am   #1
AdrianH
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Default Ideas needed to build a new 'old TV'

I have a stupid idea, which if I continue with, I will start a new thread in the Homebrew section (now moved)

I am looking to build a basic small screen 405 TV as my next lockdown project.

I am looking at the gear I have to hand, such as a small 'green' CRT DG7-5. several 7 pin EF91, EF92 valves, EB91 etc, typical of the ex military gear surplus.
Electrostatic deflection and low EHT of the DG7-5 helps here as winding the deflection coils would not be required, I can use one of my 6021 amplifier boards for any audio output and I have the cabinet ready made that was part of my 'Question on PPI or Radar' thread here:-
https://www.vintage-radio.net/forum/...d.php?t=169223
This has a mains transformer and doubler providing HT and EHT at around 900V with focus settings etc.
I could even break up and use parts of the the old Solartron CD814 scope I got going as the wife is asking me if it is going to sit there on the floor for ever!

I have started reading through the old Practical Wireless and Television magazines from 1949 and ended up with eye-strain from several hours looking at the PC screen.

So to the question of you more knowledgable people. What model/circuit diagram/era would you start from with consideration to the type of gear I have to hand. I have a couple of 6D4 Thyratron's or could happily use a Pentode in a Miller timebase circuit.

Thinking I would initially start with just the video section feeding a composite signal into it. and then work back from there adding a vision IF, then lastly sound IF and output.

Cheers from the nutter!

Adrian.
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Old 2nd Nov 2020, 8:17 am   #2
Pete_1966
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Default Re: Ideas needed to build a new 'old TV'

Check out:

http://www.worldphaco.com/ (especially the 'Argus' home built TV project.
:http://www.worldphaco.com/uploads/ARGUS.pdf)

This is an absorbing and excellent website by Dr. Hugo Holden.

Good luck with the build, especially with sourcing a CRT!
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Old 2nd Nov 2020, 8:48 am   #3
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Default Re: Ideas needed to build a new 'old TV'

A drawback of using a basic 'scope' tube for TV is that the max spot brightness distributed over the area of a full TV picture gives a very dark picture.

David
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Old 2nd Nov 2020, 9:18 am   #4
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Default Re: Ideas needed to build a new 'old TV'

Oh David, you must remember folk in the lab generating television pictures on scopes using the sweep from the timebase, a very basic frame ramp and the Z mod video signal from the backside of a spectrum analyser. Green screen but not too dim even with the high ambient light levels.

Peter
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Old 2nd Nov 2020, 9:18 am   #5
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Default Re: Ideas needed to build a new 'old TV'

Hi.
Consider using the small MW6-2 that is used in projection sets. It will give a bright focused picture at 6KV. Scan power is miniscule at this low EHT and an ECL80 will give masses of line and frame scan. I've even driven the line scan coils from my phones head phone socket!
Separate EHT is easy enough from all sorts of methods from either a ringing transformer like in the projection sets, to Chinese EHT modules and the less safe option of mains derived. Of course flyback EHT could be employed, I've even had success with Russian Rod Pentode's giving sufficient drive.
A great project to do, it reminds me to get back to my MW6 - 2 project
Good luck
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Old 2nd Nov 2020, 9:33 am   #6
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Default Re: Ideas needed to build a new 'old TV'

Hi.
This is a picture of 405 displaying test card "F" On a Hitachi scope.
Not overly bright though.
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Old 2nd Nov 2020, 10:17 am   #7
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Default Re: Ideas needed to build a new 'old TV'

Quote:
Originally Posted by Pete_1966 View Post
Check out:

http://www.worldphaco.com/ (especially the 'Argus' home built TV project.

This is an absorbing and excellent website by Dr. Hugo Holden.

Good luck with the build, especially with sourcing a CRT!
Hugo Holden is former forum member Argus25.
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Old 2nd Nov 2020, 10:55 am   #8
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Default Re: Ideas needed to build a new 'old TV'

I've heard that those 5" Chinese made sets can be converted to 405 lines with some effort.
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Old 2nd Nov 2020, 12:00 pm   #9
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Default Re: Ideas needed to build a new 'old TV'

Something to give consideration to. The shop will be forced to be closed during the lockdown so there will be no interruptions in the isolation workshop.

DFWB.
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Old 2nd Nov 2020, 12:01 pm   #10
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Default Re: Ideas needed to build a new 'old TV'

OK thanks for the responses, the one from Pete_1966 about the Argos sent me to the link and from that article, to Practical Television March 1952 and onwards for the original Argos (minus blueprint).

Then back a bit to Practical Television December 1951 for a Televisor and eventually up to Practical Television November 1952 for a Personal Televisor article using a 3 inch tube and has a reduced valve count of 10 valves with five being EF91's.

So with use of a pdf package, I plan to collate each months pages into single pdf article for ease of reading and then sit down and go through them all and try to work out my way forward.

I would very much appreciate continuing to use the collectives knowledge on matters, in that, I will produce Kicad schematics from the articles with changes relating to the gear I have available and post them here, (or in Homebrew if this steps to much into construction) for your perusal and discussion of pitfalls, obvious faults, etc.

As in the rest of my projects I plan on using KiCad and designing PCB's for my construction, initially using Turret board for any prototyping, testing checking etc. You may discern I am not a fan of using Turret boards and point to point wiring in my finished projects as all this is a learning process and that includes Kicad.

Adrian
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Old 2nd Nov 2020, 12:12 pm   #11
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Default Re: Ideas needed to build a new 'old TV'

Quote:
Originally Posted by FERNSEH View Post
Something to give consideration to. The shop will be forced to be closed during the lockdown so there will be no interruptions in the isolation workshop.

DFWB.
There is still the wife to consider when it comes to interruptions and her wishing to converse with another adult, although I do think me being classed as adult stretches the meaning somewhat!

Adrian
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Old 2nd Nov 2020, 3:45 pm   #12
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Default Re: Ideas needed to build a new 'old TV'

Quote:
Originally Posted by peter_scott View Post
Oh David, you must remember folk in the lab generating television pictures on scopes using the sweep from the timebase, a very basic frame ramp and the Z mod video signal from the backside of a spectrum analyser. Green screen but not too dim even with the high ambient light levels.
Peter
Oh, yes. That was good fun. Some background for innocent bystanders: This was in an era when the chancellor's budgets tended to knock the wind out of you. A bunch of us assembled an impromptu TV receiver one afternoon. One spectrum analyser as the RF/IF/detector another to do sound. One scope timebase doing field, another scope doing line and acting as display.

Those were scopes with 12kV EHT and we were running then too hard for longevity.

If anyone had brought a portable TV in, it wouldn't have looked like work-work Wasn't Boyd the ringleader?

David
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Old 2nd Nov 2020, 4:21 pm   #13
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Default Re: Ideas needed to build a new 'old TV'

Quote:
Originally Posted by Radio Wrangler View Post
Wasn't Boyd the ringleader?

David
Very possibly!
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Old 2nd Nov 2020, 5:44 pm   #14
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Default Re: Ideas needed to build a new 'old TV'

It is worth taking a look at how Sinclair did scanning in their (his?) electrostatically deflected TVs, quite clever.
 
Old 2nd Nov 2020, 5:58 pm   #15
AdrianH
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Default Re: Ideas needed to build a new 'old TV'

I doubt it would be with valves though?

Adrian
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Old 2nd Nov 2020, 6:07 pm   #16
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Default Re: Ideas needed to build a new 'old TV'

What's the persistence of your proposed 'scope-tube? If it's too long it could lead to some horribly-ghostly video effects!

[Though in some TV applications really-long-persistence is a good thing: such as 1970s SSTV displays where a single frame took many seconds to transmit].
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Old 2nd Nov 2020, 6:26 pm   #17
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Default Re: Ideas needed to build a new 'old TV'

The tubes I have are DG7-5 and for persistence I would go off this:-
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So a medium with 50ms down to 0.1% of spot. Not sure what a Mullard MW36-24 is as the spec sheet does not say.

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Old 2nd Nov 2020, 9:32 pm   #18
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Default Re: Ideas needed to build a new 'old TV'

Hi Adrian, plenty of designs from Prac TV over the years, although anything but basic, the Electronic Engineering and WW projects of the late 40's were very good sets.

The book "Practical Television Circuits" ( 2 or 3 different editions) has the circuits.
It would be possible to "cheat" and use a digi box for the front end and avoid the RF work and just build the TV bits.
Classical designs used the VCR97 and similar tubes, I have some like that here (ECR60's) if you need one. These were run at 2KV from a voltage doubler and are a bit safer than 6KV if mains derived

Ed
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Old 3rd Nov 2020, 1:56 am   #19
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Default Re: Ideas needed to build a new 'old TV'

Hello Ed
Up to now my favourite is the Personnel Televisor in PT over three months from November 1952 to January 1953.

The reason as laid out at the beginning of the thread, it uses the type of valves I have from the ex-military gear.
It uses a 3 inch CRT the 3BP1 which from my checking of spec sheets is really for a Vg2 of between 1500 and 2000 Volts with Vg1 between 430 and 575 Volts.

At these voltages the deflection sensitivity is comparable to the DG7-5 with its lower voltages. But! The circuit is running the Vg2 at only 650 Volts and I believe down at these Voltage levels the deflection sensitivity will be a lot better then the DG7-5. So I suspect I will therefore be adding two extra valves to the miller timebases to provide full see-saw action on the deflection plates, rather than one side fixed. This may give some flexibility for a change in CRT at some point.

The video signal is also modulating the grid of the CRT rather then the cathode and I would like to reverse these so that flyback blanking and brilliance can be applied to the grid.

I will continue to look at circuits and will do a search for the book you mention, I think this will take me a while, but I do plan to start with video and sync circuits before adding IF's.

Adrian
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Old 3rd Nov 2020, 12:57 pm   #20
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Default Re: Ideas needed to build a new 'old TV'

I have a question I need to ak the collective to better my understanding of things 'Timebase'.

I have only really looked at the Ferguson 991T with it's multi-vib style locked line time base so I can see that the time base will run on that without a signal. The old sets using thyratrons locked to sync pulses will run without a sync pulse.

But looking at the Miller Integrator, I am sure I am missing something, reading an article in PT April 1950, it appears to rely on the sync.

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If this is correct what happens on the screen of the CRT does it just leave a bright dot in the middle or does it rely on no video signal to blank off the CRT?

I believe this must be wrong, hence asking the question, in the mean time I will start to build the circuit.

Adrian
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