Philco 16M91 roundie set

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Philco 16M91 roundie set

Post by Brian Stroud on Thu Sep 27, 2012 9:13 pm

Hey everybody (and Bill Razz) I'm originally from ARF so for those of you there, I am not that new to. As for everyone else, it's a pleasure meeting you.

I started a topic on a Philco roundie that I recovered back in May. I figured I would start a duplicate of it here. Since some people may visit one forum and frequent the other and vice versa, it'll allow others who are not familiar with it to offer their input and maybe give some ideas to help it along.

This is a set that I originally found back in 2000 or somewhere around then, sitting in a corner in a run-down 1960's mobile home. The mobile home was demol'd back in May. The set still sat where it was, but they had also started knocking this apart for scrap and also to just get rid of it.

Long story short, the cabinet and convergence board were a mess, the CRT was necked, and the envelope was gone off of the 6AQ5A audio tube. The phosphour was displaced when it was necked and moisture condensation caused surface rust to form on the inside of the shadow mask and the shadow mask frame. Had those two things not happened, one colour phosphour would still have been killed by exposure. It was suggested at the time that it wasn't worth trying to fix and get going. But I'm stubborn when it comes to this kind of stuff. This is how everything looks now, and hasn't changed much since I set it down.






That's actually how the CRT looked after I started prep on removing the safety glass. The safety glass was removed a couple weeks later the same time I threw some old kitchen cabinets on the debris pile and touched them off. I gave the CRT a front row seat facing it after it got going while I took the second. Don't try with a CRT under vacuum without wearing chain mail unless you can move and work fast. Timing is everything, and if the CRT is not withdrawn soon enough and the hot safety glass removed immediately, the heat transfer will eventually cause the panel to expand and fracture at the frit line. When I was done, the safety glass was still very hot, the PVA melted to it, and the CRT panel warm to the touch. This is how it looks now.









This did not come apart when I removed the safety glass. I have the tool to cut it apart. So I cut it apart to see what I can do with it. Due to how rare good CRTs are, especially under vacuum, I played with some thoughts about this and decided to try something never before thought of. Since there is enough room inside the CRT envelope, I could build and mount onto the shadow mask frame a laser scanner mech that would essentially take the place of the electron beam and phosphour under vacuum, and run it off the deflection yoke on the neck. The picture would be displayed on the screen in the same pattern, since it would be a raster scanner with a horizontal scanning polygon mirror, and a conventional voice coil vertical mirror. So far I came up with a device that would use horizontal and vertical field detector coils that would sit inside the neck within the deflection yoke's magnetic fields. One of the field coils would also contain the secondary windings required to power the mech. I can say the secondary half of a transformer since that's essentially what it is. The horizontal scanner syncs to the horizontal detector, and the vertical scanner receives the signal from the vertical detector into an amplifier driving the mirror's voice coils. I don't have the schematics for the set so I do not know where the beam switching takes place. In SS sets, the beam switching takes place in the CRT drivers connected to kr/g/b. In tube sets, I don't know if it takes place at k, g2, or g1. I haven't started building the scanner mech yet.

So far I've got as far as determining what I have already, getting a nice handful of 6AQ5A's from one of the guys at Sunshine Radio Museum in Sodus, NY, worth a go if you're ever around there, and deciding the first thing to hit was going to be the main filter caps and audio IF board, getting those areas recapped, that way I can get a feeling for it and a good idea how to approach it too.

This one is certainly going to be a while. Since I got this I got another telly to work on too. By the time I get done with that one, I'll know what I'm doing when I tackle this one.

Brian Stroud
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Number of posts : 13
Registration date : 2012-09-27

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