Sixties Tube TV Hack to Accept Composite Video

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
Hi folks

as title, i have a sixties Italian made TV that (duh!!) don't have any video in or out (it seems to have an audio out), the problem, as some may understand, is that i cannot receive any analog signal and it would still be neat to see something without headscratching on PAL-to-VHF boxes\circuits that i don't have (only UHF) and it's waaay nicer as a monitor

fact is that i haven't started to lay my hands on it but the last time i saw it in action it was showing at least noise, i can provide a schematic, problem is that i din't find any "spot" to tack an RCA on, anything seems messy and multi-line and i'm not "duper" on those, the only thing i know is that the analog signal it receives is basically composite video on carrier (and subcarried sound)

any tought, suggestion, or else is appreciated
 

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
UPDATE:
it seems i missed an UHF tuner expansion on the TV, i don't know (and i dubt) that it can be a composite video in, it may be an IF in or something, those tuners usually had like 3 transistors, i don't think they are easy to replicate from a PAL signal
 

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
Power supply
yeah, i know, but there's no separate power supply, just the classic double winding and two tube diodes.... maybe you meant that i live in 115V land and it's a 220V, nope :) i live in 220V land

Try the contrast control open wiper to inject composite into the TV. Hope is transistorized. Perhaps trough a capacitor to isolate any DC...
no transistors, just a pair of OA85 diodes (that i haven't spotted) as solid state stuff

yeah, the contrast zone looks feasible, honestly there's some scoping examples but none look familiar with composite and they seem to cover other processed signals

i'm starting to fix this pile of dirt, it doesn't seem too bad, at the times we changed some elec caps for safety, the rest seems 99% in shape, i think tomorrow i will "plug the plug"

ok, i'm uploading the schematic and stuff, beware it's italian, you may find something like "àèéìòù" LOL ... no need to keep it secret
schematic 1of2.jpg schematic 2of2.jpg other 1of2.jpg other 2of2.jpg
 

Dodgydave

Joined Jun 22, 2012
8,472
Your tube driver is Valve V91? a PCL84, , you can inject the video there at K103 coil,,but you need to also the Sync pulses for the Line/Frame timebases at sync separater V901B, a .12ET1 valve.
 
Last edited:

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
Your tube driver is Valve V9?? a PCL84, , you can inject the video there at K103 coil,,but you need to also the Sync pulses for the Line/Frame timebases at sync separater VT1, a .12ET1 valve.
YES!! i downloaded this book http://www.introni.it/pdf/Ravalico - Il Videolibro 1961.pdf and after a bit of read trough (i was starting to get an idea anyways) i realised the PCL84 was carrying the whole, it appears it's an old system that carries the sound along the video, used early, that's why i was confused by the audio section hooked to the PCL84 cathode (no need to worry for that i guess)

but just a question (to avoid too many headscratches) isn't the sync and stuff already carried out from there?... i mean, the sheet says 1V to 6V signal, isn't the 12ET1 driven by from that diode? i intend to build a video amplifier to suit that levels (hopefully) and my convinction is that the sync system will follow the amplified composite video in
 

Dodgydave

Joined Jun 22, 2012
8,472
Yes the Sync separater is the V901B valve, tapped off the Video output, so you need to inject the Composite Video into both of these points, to see if it will work,, Use a DC blocking Capacitor for safety.
 
Hi, Guys
The set looks very similar to American sets from the same era, with the sound carrier generated by beating the audio and video carriers together in the video detector diode. Now, to use this as a video monitor, you would inject your video through a suitable capacitor anywhere after the video detector diode, up to the video output grid. A 0.22 uf cap would probably be big enough. Both sync and AGC (which you won't be needing) are tapped off the plate of the video output. For the sound, stick it in at the top of the volume control, again through a suitable capacitor, 0.01 to 0.047 or so uf. This will work as long as you have a PAL video source with negative sync. It might be able to be modified to work with NTSC but getting the high voltage right could be tricky. You'd need to "shrink" the grid and plate timing caps in the vertical oscillator to get it up to 60 hertz, and you'd have to add some cap to the horizontal oscillator and output circuits to get it to work right at 15734/15750 hertz.

The main worry here is that this is a hot chassis set, and your return connections (coax braid) will be at AC line voltage. Not a good thing.
 

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
yes, that's the idea for now, but currently uummhh *scratches his beard* the TV isn't working much, there's nothing on the screen, i have to repair it, hopefully with the least work implied, the horizontal tube seems oscillating.... i think i can already change all the paper and oil caps and checking the "interesting" resistors (i hate those old ones)

i also tought about reducing the cathode resistor on the PCL84 to accept a lower signal, the sync might follow this idea

i live in 220V PAL land

yeah, the audio side wouldn't be so complex to hack, it already makes some disturbing noise :D

yes, the chassis is live, or at 125V, i have to tilt it somehow to turn it on while messing on the underside, i might use my crappy DIY isolated probe on the scope, i also considered fitting a modern board from a color TV but the CRT connections aren't convincing enough and all the knobs would be just aesthetic :S
 

DickCappels

Joined Aug 21, 2008
5,944
If the chassis is hot you might consider either adding an isolation transformer between the 220V and the chassis, then groundnthe chassis. That will not only protect your life but also any equipment you comnect to your monitor.
 
Somewhere around Y2K I was working on a Samsung CRT type solid state TV in warranty. I had the board out, scope and antenna connected, and ready to apply power. Just then the boss decided it was a good time to bend my ear. For some reason I plugged the AC cord into the AC outlet instead of the little power strip connected to the isolation transformer. BOP! 83 volts RMS connected to ground through the scope probe and the antenna coax. I'm glad I had the coax connected because the scope was one of the 3200 dollar Sencore 60 meg jobs with the built-in DVM, with the $200 probes, so it wasn't damaged. Not so for the TV. It was roughly comparable to a lightning strike through the AC line to a cable connected TV. Blown tuner, blown foil, multiple dead semiconductors including the video - chroma jungle IC.

I got a set of "kid caps" for the AC strip. Just as a reminder.
 

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
yeah, i need to arrange an isolation transformer, fact is that i have one but it's only 70W and i dubt it can hold the TV, i have to put a pair in series to have like 140V (80+60) and change the selector (now the situation becomes lucky)
 

MisterBill2

Joined Jan 23, 2018
4,055
The safe way to utilize this set for a video monitor is with an RF adapter that typically transmits on channel 3 to the TV set also tuned to channel 3. Doing that you can have adequate isolation and avoid any shock or damage hazards from getting inside the set. The problem is that composite video also contains the synch pulses and there may not be a point in the TV circuit where that input would work. And almost every scrap VCR contains one of those little transmitter modules, so they are easily available.
 

Thread Starter

BulbChangeExpert

Joined Mar 26, 2016
54
The safe way to utilize this set for a video monitor is with an RF adapter that typically transmits on channel 3 to the TV set also tuned to channel 3. Doing that you can have adequate isolation and avoid any shock or damage hazards from getting inside the set. The problem is that composite video also contains the synch pulses and there may not be a point in the TV circuit where that input would work. And almost every scrap VCR contains one of those little transmitter modules, so they are easily available.
i have a pair of those but they are all UHF, besides, i think that using composide video avoids me to mess with radio circuits that i honestly don't want to fix\adjust, and it will (supposedly) work better

yeah, i know, the system will be live, but apart playing a bit of SNES and proofing the system i intend to let the TV stay mostly unused, i have better stuff from already the nineties :D

the sync signal should be included, it's a matter of tuning the sync circuits, we already discussed this

i intend to re-start fixing this thing as soon as possible, luckily the tubes seem little used and original
 

MisterBill2

Joined Jan 23, 2018
4,055
i have a pair of those but they are all UHF, besides, i think that using composide video avoids me to mess with radio circuits that i honestly don't want to fix\adjust, and it will (supposedly) work better

yeah, i know, the system will be live, but apart playing a bit of SNES and proofing the system i intend to let the TV stay mostly unused, i have better stuff from already the nineties :D

the sync signal should be included, it's a matter of tuning the sync circuits, we already discussed this

i intend to re-start fixing this thing as soon as possible, luckily the tubes seem little used and original
GOOD LUCK!!!
 
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