Best way to feed in composite or s-video luma to a B&W Tube set?
 

I've been looking for info on this and wondered if anyone had some good resources for a way to add support for composite (or S-V luma) to a B&W tube set (specifically, my fleetwood I'm restoring in another thread here).

I've found a few things but they seem to be rather outdated and/or the links/reference material no longer work, so I was hoping someone here might have some thoughts.

I gather direct circuit mods aren't easily done without additional SS circuitry owing to the different nature and impedance of tube drive signals.

I do see cheap RF modulators littered all over fleabay, and even B-Ts can be had for $40 or so including shipping - except the BTs aready require a 75 ohm coax signal in.

Any comments/thoughts on cheap RF modulators and how capable they are - or is it better to make a small drop-in SS module to amplify the signal?

I would assume the signal level on the cheap-o mods isn't high enough to be able to transmit wirelessly, unlike what I've seen some folks here do with the B-Ts.

I had one of those cheap-o RF modulators that worked fine. Think it was a Coby. It was so cheap, it didn't even have an on/off switch :)

If your set has external antenna screw terminals, a simple 75-300 ohm adapter will get you in. You may need an RF attenuator if the RF modulator you choose has high output, and your tuner is really sensitive... You'll have to experiment.

In theory, you could place a transmit antenna inches away from your receive antenna... but I've never done it.

Chip

I do indeed have two of those adapters on hand.

Browsing DX, I found this which looks like a 2 in one:
http://dx.com/p/gecen-gc-av04-househ...-silver-231907


Can anyone comment on that? I know it's 230V but I've got a eurotransformer kicking around here somewhere.

Edit: I guess what I'm looking for is something that can be used as a broadcast modulator to serve multiple TVs, but if that can't be had for a cheap price a $10 bay jobbie will do.

Do I need to worry about NTSC/PAL, or do most modulators do the RF bit regardless of the input signal type?

S-Video is already 75 ohm impedance, and the luma channel will drive a 75 ohm load into a modulator just fine. All you'd need is an S-Video cable with an S-Video connector on one end, and a pair of RCA jacks on the other. One of those RCA jacks is the luma. You may also need an RCA to BNC adapter.

As for the standards, you'd want to be sure to get one intended for NTSC, so the sound subcarrier is on 4.5MHz, and not 5.5 or 6.5 for some PAL countries.

Yes, I came across a section on antiqueradios.org about rf modulating where I read it could just be done with an RCA->F adapter.

I think I have an old VCR somewhere I can adapt for now and then just browse "that place" for a good deal on a BT. The ones I found earlier were mid-band so of no use to those of us that deal in tvs with channels that don't go that high.

A modulator just modulates. It doesn't know about PAL, NTSC, 60Hz, 50Hz etc. you need the right vision polarity (negative, most modulators will be OK here anyway), sound system (FM) and sound spacing (4.5MHz for the US system). Any modulator sold for use in the US should be fine.

If you put an NTSC composite signal into a modulator is will work OK with a monochrome set. Just as it always did when receiving colour signals on a mono set. One of the most important things about NTSC (and PAL, SECAM) was they were COMPATIBLE. THis meant that existing mono sets worked with the new colour signals while colour sets could also receive the old monochrome ones.

The only downside on a mono set was you would see some fine patterning in coloured parts of the picture. The subcarrier frequency was chosen to minimise this problem. PAL is rather better than NTSC in this respect.

As other have said, the Y part of an S-video feed (or the Y signal from a 3 wire YUV/YCbCr connection) is exactly a monochrome signal.