Philco Safari Video Input

[mr_rye89]

Has anyone here tried injecting composite video into a Safari? I tried injecting it AFTER the video detector and I get a "negative" looking picture (almost like the luma signal is inverted) with poor horizontal linearity/lock.....

[Electronic M]

It is possible you do have negative lumina. Every stage of video amplification inverts video polarity* and IIRC the even VS odd number of IF amps in any given model changes the necessary detector/video output of detector polarity. The CRT can take either polarity as long as you choose the correct element (grid or cathode) to drive.

Been a while since I looked at the schematic of these but you might try injecting one video stage closer to CRT than you are. That will probably invert the polarity. If it doesn't and or video is too weak you may need to add a video amp stage possibly with inversion.

* In tube sets amplifier circuits typically are inverting, but if you choose/encounter a topology other than the stereotypical grid/base in, plate/collector out(IIRC that is called common cathode/emitter) there are non-inverting single stage amp topologies.

[mr_rye89]

Ok I'll see if it will work after the video amp. I'd figured it would be something like an inverting (quite literally) stage. I can probably whip up a non inverting video amp if I need it. I'll see if I can post that bit of the schematic later.

[old_tv_nut]

Just a quick note - the number of IF stages does not make a difference in video polarity, only the orientation of the detector diode and the number of inverting video stages does.

[mr_rye89]

I got it to work.

Inject video at the base of the video output transistor as indicated by the red arrow. use a DC blocking capacitor in series as there is 10-11 volts there. Audio works just tied to the volume pot wiper of course. Now I'll wire up some pigtails/a switch and stuff a Roku in the battery compartment

[mr_rye89]

No control over contrast. I'm going to try it before the contrast pot later........