Scart on old telly?

[hans]

I have a late 60's ITT tv with a broken tuner. I would like to connect this set to a dvd/vcr.

I have some old insulating transformers from old Grundig sets i could use, but is it possible to connect the signals from modern source easily to this old hybrid set?

I have no scematics/service manual for this set. (ITT Kansas) Anyone know where i can get one?

[ben]

This sort of thing is generally no picnic.
It will probably take you far longer to investigate the signal path, make the necessary mods, provide adequate safe connections for the composite input, and signal switching, than to just replace the broken tuner and use RF. maybe put a post in the forum wanted area? a jpeg of the broken tuner would also help.

[Brian R Pateman]

It would be unusual for the tuner to be anything special in a set of this vintage. It would be far easier to repair the existing tuner or replace it with a tuner from a contemporary set than going to all the trouble of developing the interface circuits necessary for this sort of modification.

Regards,

[murphyv310]

Hi.
There are at least 2 ways to feed baseband video into a set, one thing paramount is safety, most sets of this era will have a live chassis, in other words one leg of the mains is connected to chassis. You will need to have an isolation transformer or feed the video and audio via opto couplers.
Aside this most DVD or VCR recorders will give 1v p-p output but ideally you need 2.5v p-p to drive a Video amp valve properly plus this needs to be variable to act as a contrast control.
I would say don't give up as it can work and work very well.
If you have a diagram PM me with it and I will show you what to do.
Cheers
Trevor

[Jimmyhaflinger]

Is it possible to feed a composite signal in an early all-transistor B/W set? no problems with live chassis here as the whole set is running on a 12 volts power supply!

Maybe on the input side of the contrast pot?

i have a late 60s Voxson 23" (tabletop) solid state set with bad IF stages and i'd like to put it to good use!

[Steve_P]

It's possible to feed Baseband Video into any TV if the right precautions are followed.

Capacitors to isolate the chassis. Then find a place to feed it in. Video and Sound separately. You may have to add Amp stages in each case to bring the video up and sound up.

Yes, it can be done. But be careful how you do it.

What's up with the ITT tuner by the way?

Cheers,

Steve P.

[murphyv310]

Originally Posted by Steve_P

It's possible to feed Baseband Video into any TV if the right precautions are followed.

Capacitors to isolate the chassis. Then find a place to feed it in. Video and Sound separately. You may have to add Amp stages in each case to bring the video up and sound up.

Cheers,

Steve P.

Hi.
Caps to isolate the chassis can introduce hum and I wouldn't really trust them, also Caps to isolate removes the DC content from the video signal. Mains isolating transformers are the easiest way but are expensive and bulky, one reason I suggest Opto-Couplers, 100% isolation and a huge bandwidth, Iv'e done it and it works perfectly.
Trevor

[murphyv310]

Originally Posted by Jimmyhaflinger

Is it possible to feed a composite signal in an early all-transistor B/W set? no problems with live chassis here as the whole set is running on a 12 volts power supply!

Maybe on the input side of the contrast pot?

i have a late 60s Voxson 23" (tabletop) solid state set with bad IF stages and i'd like to put it to good use!

Hi
Yes most 12v transistor sets are quite easy, you may be able to feed video to the contrast control, but most contrast controls actually adjust the gain of the Tuner and IF strip or just the IF strip.
A quick look at the circuit will reveal all.
Trevor

[ppppenguin]

Originally Posted by Steve_P

Capacitors to isolate the chassis.....

Much as hate to disagree with my old friend Steve P, what he has suggested is downright dangerous. If the caps are small enough for safety they will mangle the video waveform (might just about do audio in a high impedance circuit). If they are big enough to pass video then they will pass too much mains for comfort if the chassis is live.

As Trevor says, an isolating TX is expensive and bulky. I've experimented with opto coupling for video but never got terribly good results. Maybe it's because it was many years ago when optos were a bit slow. It would be nice to see some circuits and suggested devices.

You can actually buy VIDEO isolating transformers. Expensive things usually used to break hum loops in pro studio systems. I've no idea how they get them to cover enough octaves to work.

[HG MICKE]

Some years ago Hitachi used opto isolators for audio and video, for connecting a scart to a set with a live chasis. unfortunately I cannot remember the model number but the set was made about 15 years ago.

Colin

[murphyv310]

Originally Posted by ppppenguin

As Trevor says, an isolating TX is expensive and bulky. I've experimented with opto coupling for video but never got terribly good results. Maybe it's because it was many years ago when optos were a bit slow. It would be nice to see some circuits and suggested devices.

Hello.

the Panasonic TX1485 used Opto's for their AV inputs and I used the small board from a scrap set in a Pye D18T with total success.
Cheers
Trevor

[Nickthedentist]

Originally Posted by HG MICKE

Some years ago Hitachi used opto isolators for audio and video,

Yes, you're right. I may have the circuit/model number at home.

Nick.

[Michael Maurice]

Originally Posted by Nickthedentist

Yes, you're right. I may have the circuit/model number at home.

Nick.

It was the C2509 and there were 14" & 17" versions as well.

I just took a quick look at the circuit, it requires a supply to the scart end of the circuit. This supply is taken from a winding off the LOPT, rectified and smoothed. Pulse transformers are quite suitable for this application and available from RS and farnell.

Here's that part of the C2509 diagram that has the scart socket and optocouplers.

[murphyv310]

Originally Posted by Michael Maurice

It was the C2509 and there were 14" & 17" versions as well.
Here's that part of the C2509 diagram that has the scart socket and optocouplers.

Hi
The Circuit of the Hitachi is simpler than in the Panasonic so I would use this one, remember you need more than 1v p-p (usually 2-2.5v) to drive a valve video amp and a level control to use as contrast.
You guys have good memories must be at least 10000GB
Cheers
Trevor

[llama]

I like that c2509 method a lot.
Now if someone could run off some PCBs - maybe with an RGB version thrown in for good measure...

One more approach for completeness, though not necessarily recommended in this day and age, is to use the Rediffusion method as delivered by the "Telebox". Modulate the video onto about 10MHz (from memory) and feed that via a pair of high voltage, lowish value capacitors into the video demod. (Audio went straight to the speaker).

Graham

[Michael Maurice]

Originally Posted by llama

I like that c2509 method a lot.
Now if someone could run off some PCBs - maybe with an RGB version thrown in for good measure...

One more approach for completeness, though not necessarily recommended in this day and age, is to use the Rediffusion method as delivered by the "Telebox". Modulate the video onto about 10MHz (from memory) and feed that via a pair of high voltage, lowish value capacitors into the video demod. (Audio went straight to the speaker).

Graham

If you're going to go to that length, you might as well fix the tuner!

[tech-master]

hi,
the easiest way would be to repair the tuner itself , and connect an
"R.F modulator" to the the tuner , and tune in the dvd,freeview, etc..(problem solved!)

the company who repairs tuners is called "M.C.E.S" in birmingham (uk)
as they will repair it and re-align the uhf frequency for you at a reasonable cost!

cheap R.F modulators can be obtained/bought at "C.P.C"
in Preston ,Lancs,(uk)

hope that helps,

Tech-master.

[Nickthedentist]

Originally Posted by tech-master

the company who repairs tuners is called "M.C.E.S" in birmingham (uk)
as they will repair it and re-align the uhf frequency for you at a reasonable cost!

Sadly, they closed down last year (I think), but I understand that one of their workers is carrying on some of their services.

Nick.

[murphyv310]

Originally Posted by Nickthedentist

Sadly, they closed down last year (I think), but I understand that one of their workers is carrying on some of their services.

Nick.

Hi Nick.
Yes MCES has closed down but a UHF pushbutton tuner was sent off to the new company 3 or so months ago and returned with the note that they had no parts for older tuners. Sorry!!
Cheers
Trevor

[tech-master]

hi,
you could try phoning an old friend of mine,
who specializes in pre 1974 TV sets , and spare parts,
who might have an old ITT tv tuner for you?

Please PM me for the name and telephone number.

Regards,
Tech-Master.