Getting the bug.

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Getting the bug.

Postby murphyv310 » Tue Oct 24, 2017 9:35 pm

Hi.
After the success with my modified Bush TV22 and able to resolve obsolete electronic standards from 120/24p to 240/25p I thought id have a go trying to resolve mechanical standards on the scope.
I'd already built a small board comprising a single transistor for video inversion and of course more drive, a sync seperator using a 1881 chip and a sawtooth generator for field scan using a 555 timer chip. This was a total success with excellent results from 819 lines down to the German 180 line system.
DSCF8833.JPG
180 lines on Hitachi scope


50/25p50/25p96/25p


So yesterday i thought I'd have a go using some of the Mechanical standards generated by my 2004 Aurora Multistandard converter. I fed the input with a 625 line test card "F", The generator produces a sine wave from one audio channel to sync up or drive a motor for the mechanical standards but the sine wave is of course related to the video signal so can be utilised for sync. Even with just the sine wave the scope will lock perfectly and oddly enough in most cases the 1881 chip produces some weak pulses for the 555 timer to lock onto, My time base will run down to just a few hertz96/25p so all frame rates are accommodated.
Here are a few samples i took yesterday.

DSCF8967.JPG
60/25p
DSCF8970.JPG
30/12.5p TeKaDe
DSCF8965.JPG
30/12.5p Baird


Sorry something has gone amiss with the pictures and the comments.

Anyway I have the bug biting at me now so i'm now considering building a small monitor, I've a fair selection of old small Green screen tubes.
Cheers Trevor.
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Re: Getting the bug.

Postby murphyv310 » Wed Oct 25, 2017 1:52 am

Hi.
Sorry but I've posted this in the mechanical section.
Could a moderator move it to the Electronic section please :D
Cheers Trevor.
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Re: Getting the bug.

Postby murphyv310 » Wed Oct 25, 2017 8:19 am

Hi.
I've a couple of VCR 97's also two VCR139A tubes, I've some MW6/2 two inch projection tubes, I've successfully run these at much reduced brightness for direct view at 7kv EHT. I'm now thinking of making a dedicated monitor for the lowest standards say between 30 & 96 lines.
I'd be interested in hearing what way to go.
Cheers Trevor.
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Re: Getting the bug.

Postby Harry Dalek » Wed Oct 25, 2017 7:39 pm

murphyv310 wrote:Hi.
I've a couple of VCR 97's also two VCR139A tubes, I've some MW6/2 two inch projection tubes, I've successfully run these at much reduced brightness for direct view at 7kv EHT. I'm now thinking of making a dedicated monitor for the lowest standards say between 30 & 96 lines.
I'd be interested in hearing what way to go.


Hi Trevor
Yes The vcr139A will work for sure ! lower voltages too for this tube.
viewtopic.php?f=31&t=2387
viewtopic.php?f=31&t=2391
Circuits for this there ..
Do you have your scope circuits trevor handy ?it seems to work very well ....
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Getting the bug.

Postby Panrock » Thu Oct 26, 2017 5:25 am

I remember how the Henry's Radio catalogue in the '60s listed the EHT for the VCR139A as only 400v. A natural choice then, for a 16 year-old Panrock with his first NBTV receiver! (This was an astonishingly crude set that also used neons in series for the timebases but that's another story).

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Re: Getting the bug.

Postby murphyv310 » Fri Oct 27, 2017 9:32 pm

Hi.
I do have the circuit for my little board for driving the scope.
I'll post it up over the weekend.

Incidentally I've even managed to get 60/25p on the modded TV22.... amazed to say the least.
Will post up on the appropriate thread soon.
Cheers Trevor.
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Re: Getting the bug.

Postby Harry Dalek » Fri Oct 27, 2017 11:33 pm

murphyv310 wrote:Hi.
I do have the circuit for my little board for driving the scope.
I'll post it up over the weekend.

Incidentally I've even managed to get 60/25p on the modded TV22.... amazed to say the least.
Will post up on the appropriate thread soon.


Thanks Trevor i was surprised the lm1881 worked in the lower line rate's which is good to know any good circuits like yours simple and works well will be handy for others and me too .
Yes 60 line on that tv will be interesting to see do post up pic's .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Getting the bug.

Postby murphyv310 » Fri Oct 27, 2017 11:49 pm

IMAG0545.jpg

Hi.
Here is the circuit of the board I made up.
On mechanical standards so far I am using the Sine wave sync from the Aurora's audio output.
This allows the scope to lock. Frame is a bit hit and miss but the LM1881 is doing something with weak pulses going to the 555.
I need to investigate further and see exactly what is happening.
Cheers Trevor.
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Re: Getting the bug.

Postby Harry Dalek » Sat Oct 28, 2017 8:07 am

murphyv310 wrote:
IMAG0545.jpg

Hi.
Here is the circuit of the board I made up.
On mechanical standards so far I am using the Sine wave sync from the Aurora's audio output.
This allows the scope to lock. Frame is a bit hit and miss but the LM1881 is doing something with weak pulses going to the 555.
I need to investigate further and see exactly what is happening.


Thanks Trevor i am studying the circuit I will give it a go when i have time ,might be just the thing for my monitor ,at the moment i am just going to have it as a slave to the PMT camera like a view finder but this would be some thing i could add and try later on..
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Getting the bug.

Postby murphyv310 » Sat Oct 28, 2017 7:59 pm

Thanks Harry.
Since I made this board up I've changed the charging cap for the 555 to a non polarized type of 2.2uf.
Also added a switch that shorts out one diode in the constant current chain to switch to 25Hz, a further one can be bridged just leaving one for 12.5Hz.
Cheers Trevor.
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Re: Getting the bug.

Postby Harry Dalek » Sat Oct 28, 2017 10:49 pm

murphyv310 wrote:Thanks Harry.
Since I made this board up I've changed the charging cap for the 555 to a non polarized type of 2.2uf.
Also added a switch that shorts out one diode in the constant current chain to switch to 25Hz, a further one can be bridged just leaving one for 12.5Hz.


Great Trevor the tips will come in handy when i make a copy for your circuit ,i was thinking about it again think i leave it to a scope monitor least for testing .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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