video monitor with DG7-32

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

video monitor with DG7-32

Postby Didi » Wed Jun 26, 2013 2:51 am

Hi Steve,
thank you very much for your advices. I want to use the 250 V secondary voltage of the transformer. That would be no problem. Meanwhile I searched in my workshop for the components that are necessary to build the CRT power supply.
Today I'll start with it.
I'll try to use the EL84 part of the crap schematic for the video amp.I hope this is OK.
This is the link of it:
https://www.dropbox.com/s/6ysoao5sgu1gc5d/3.jpg
I 'll use your version for the deflection unit cause it's a simple one and easy to build.
Today I got from ebay some 2N2222 and I've tested some used ECC91 with my tubetester and their emission is over 100 percent :-))
The only thing that's missing are the hoizontol and vertical controls with pots like it's made in the old crap schematic that I sent first.
I hope that there's no need for additional deflection amps and that it's possible to connect the EL84 x,y output directly to the deflection unit that you suggested.
If the schematic is working and I've got some experience with it then it could be the right time
to make some improvement if it's necessary.

kind regards
Didi
l
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Postby Steve Anderson » Wed Jun 26, 2013 1:39 pm

The problem with the CRT circuit you've chosen is there are no position controls. To add them would require dropping the voltage across the CRT which will result in a dimmer picture and a larger spot size (defocussing). So I don't recommend this circuit in this application...even though it is one of mine. The DG7-32 isn't the brightest of tubes when used in raster applications like this, it's fine in oscilloscope applications where effectively there is only one line.

Although there are 'position' controls shown in the ECC91 circuit they will only function when the anodes of the triodes are directly (DC) coupled to the deflection plates, this removes those four capacitors and the four 4M7 resistors.

Now the average voltage of the deflection plates is around +200V and the final anode of the CRT (pin 8) needs to be the same +200V.. This requires the cathode to sit at around -400V and the grid up to 120V more negative (-520V).

This is quite easy if you have a 250V AC out transformer, it's even easier if you have a 250-0-250V version.

If you change the ECC91s to ECC81s you may need to reduce the gain of the deflection amps by increasing the value of the resistors in the cathodes, four places, all equal, due to the higher mu of the ECC81. From memory the input sawtooth to each amplifier needs to be around 4V p-p. If this is the direction you intend to go I'll draw up a circuit...it's quite easy, just a cut-and-paste exercise and changing a few component values.

With hindsight I would have suggested ECC83s as replacements for the ECC91s as they are a lower current tube, An ECC81 running at 1mA is running very 'light' and may not be that linear...but I've been wrong in the past!

The EL84 as the video amp is a bit of overkill, it's somewhat of a gas-guzzler (power). A small RF pentode, say an EF91 or EF80, would easily do the job.

Your thoughts?

Steve A.
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video monitor with DG7-32

Postby Didi » Thu Jun 27, 2013 3:18 am

Hi Steve,
I'm sorry but I'm a little confused because in the CRT related schematics I don't have much experience.
I think for the first try I'll use the deflection schematic with the 2 ECC91 to make the whole project a little easier.
Is it possible to connect the xy outputs of the videoamp directly, without the usage of an aditional deflection amp, to the deflection unit?
Is it possible to use the following CRT schematic with some changes in the components to get a cathode ( pin 3) voltage of - 400V and a grid 1 ( pin2 ) voltage of – 520 V like you
suggested to me?

http://www.taswegian.com/NBTV/forum/fil ... it_559.gif

I own a variable isolation transformer ( a combination of an isolation and variable transformer ) for the power supply that has a range from 0-250V.
Is it possible that you publish the CRT schematic with this changes that are necessary to run the CRT with the position controlls?
I own a lot of EF80's and some EL84 for the video amp. The problem is that I don't know the values of the components if I use another tube like the EF80.

kind regards

Didi
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video monitor with DG7-32

Postby Didi » Sat Jun 29, 2013 4:32 am

Hi to all,
recently I saw on this site some variations how to build a PSU for the DG7-32.
For example this one:

http://www.taswegian.com/NBTV/forum/fil ... it_559.gif

The problem is that I don't know how to connect the grid 1 of the CRT ( PIN 2 )
with the rest of the schematic.
Is someone able to give me any advises?
Thank you very much for your efforts.


kind regards

Didi
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Postby Steve Anderson » Sat Jun 29, 2013 1:06 pm

Didi, sorry for the slow response, it's been busy here over the past few days...

Now, I think you are rushing at this hoping that if you throw a few random circuits together it will 'work'. The arrangement of the PSU and the manner of deflection determines almost everything else. This needs to come from you. DC or AC-coupled deflection? AC or DC-coupled video drive to the grid? (DC-coupled video to the grid using tubes is not easy, there are no 'PNP' tubes sadly).

I am quite willing to help here, but I still don't know really what tubes you have and where you wish to use them. All I do know is you have an isolated variable transformer for the HT supply.

You may get a few ideas from this guys web-site, he's a member here but rarely these days posts...

http://www.freewebs.com/cameramanlink/e ... ojects.htm

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video monitor with DG7-32

Postby Didi » Sat Jun 29, 2013 8:15 pm

Hi Steve,
thank you for your answer. Reagarding the monitor circuit I don't prefer a ''special'' version.
It would be very nice if you're able to give me a CRT schematic that fits to a deflection and videoamp unit.
Reagarding the tubes they should be german types like EL84 , EF80's, Ecc81, ECC91 ECC83. I bought some 2N2222 transistors and ECC91 for the deflection unit.
If it's necessary I'm able to get other ones from ebay or a german tube seller.Thats no problem.
I don't want to reach a absolute perfect picture quality, for the first try I want to build a monitor that delivers an average quality so I'm able to make some experiments with it and to get some basic
experience and knowledge with this new area of tube technology.
If it's possible to use a EL84 for the videoamp and it'll work it doesn't matter if its a little overload.
I'm sorry perhaps there are some misunderstandings in our discussion because English is not my native language.
About the deflection unit you wrote:
''DC or AC-coupled deflection? AC or DC-coupled video drive to
the grid? ''
If a AC coupling is easier I'll prefer this way.
It would be very kind if you're able to send a CRT schematic with deflection unit and video amp
If it's possible to avoid an aditional deflection amp it would be nice if not are you able to ad a deflection amp too?
I'm sorry that I ask you so much but you're the only one that really knows the basics of the CRT schematic and from which I get the informations that are necessary to build a project like this one.
I know the'' cameraman'', his site and youtube videos, they're very nice. I wrote him 9 days ago
but there was no response.

kind regards
Didi
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video monitor with DG7-32

Postby Didi » Fri Jul 05, 2013 4:17 am

Hi Steve,
thank you very much for your efforts regarding the DG7-32 monitor circuit.
Two days ago I got some PCB pieces that I ordered at ebay.
Now I think I have enough material to build a very nice monitor with the DG7-32.
I got some ECC91 tubes for the deflection unit too.
I think there are some details in the schematic that have to be changed to fit to the DG7-32.
I know you have little time at the moment but it would be great for me to work a little on the schematic in the following days.
Is it necessary to make changes on the deflection unit with the ECC91 that you suggested ?
If I get the monitor to run I'll publish some pics/ movies for the other members of the forum.

kind regards

Didi
Didi
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video monitor with DG7-32

Postby Didi » Sat Jul 06, 2013 3:23 am

Hi to all members of the forum,
if anyone has schematics that fit to my project please don't hesitate to publish them at the forum.
All suggestions are welcome.

kind regards
Didi
Didi
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Re: video monitor with DG7-32

Postby Doz » Fri Sep 26, 2014 8:33 pm

Hi Didi,

Mine's rubbish, but it's here:

http://andydoz.blogspot.co.uk/2014/09/s ... -tube.html

Thanks.
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Re: video monitor with DG7-32

Postby Doz » Fri Oct 03, 2014 9:27 pm

Hi All,

I created a very simple video monitor a while back using this tube. There's a schematic on my website.

http://andydoz.blogspot.co.uk/2014/09/simple-tv-using-dg7-32-scope-tube.html
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Re: video monitor with DG7-32

Postby Steve Anderson » Thu Oct 09, 2014 7:20 pm

Hi Andy (or is it Doz?),

Not tried 625 on a DG7-32, should be OK though. Two things, you may be getting ripple/hum in somewhere, and the retrace is visible perhaps because the video signal is AC-coupled to the CRT grid circuit. That second issue isn't that easy to get around, but from what I see, well done!

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Re: video monitor with DG7-32

Postby Doz » Wed Oct 15, 2014 10:26 pm

The ripple appears to be a camera artifact, because it's invisible in normal use.

It was only an exercise really, although I may dig it out again and come up with some plan to sort out some flyback supression.
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Re: video monitor with DG7-32

Postby Steve Anderson » Thu Oct 16, 2014 3:27 pm

Doz, if you received a warning r.e. your previous post, please ignore it - I hit a wrong button instead of the 'approve' one...

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