Gilfillan Prototype Set

[dtvmcdonald]

When color TV was new, RCA made available the special needed parts. These
really included only deflection yokes, convergence coils, and horizontal output transformers, though others
could get the color transformers as well. Everything else could be standard parts, at least for sets using 21AXP22s and later CRTs.
RCA actually encouraged others to make their own designs. They didn't care ... they'd
get the royalties anyway. At least, if any of the sets actually sold.

[Electronic M]

Nice score, Nick!

RCA did not hold patent on all possible circuits that could demodulate color. GE had an earlier 15GP22 based set that used their own original chroma demod circuit that did not use an oscillator (and GE kept using that thru the end of the tube era). Look at some of the 60's designs like Zenith's beam gate demodulator or Motorola's (or was it Admiral?) single tube self-oscillating demodulator....The former I would not be surprised if Zenith had designed back in their 1954 prototypes. Magnetic convergence was also a Zenith design (RCA's 15GP22 was electrostatic convergence, and they would have kept making them had others not passed them by). The QAM color signaling method it's self was Philco's idea. The reason most makers went with RCA clones is that it was usually easier/cheaper than to make it your self....At least until profitable volume was selling.

[Sandy G]

Looks to me you've got a JIM-DANDY new Playpretty... W/your technical smarts, I expect to see it makin' "Glorious Lollipop Color" very soon... (grin)

[miniman82]

You should have your friend post his up, we could make it a Gilfillan only thread.

[miniman82]

So here's how I decided to repair the flyback, whose wax tire had decided to fall off in chunks over the years.


First a before shot, all dirty and nasty. This flyback is unique just like the one in the 21-CT-55, because it has one of the filament windings for the rectifiers right there on the tire. There are also 2 other filament strings, wrapped around the ferrite core. I think it had to be done this way, because there simply wasn't room elsewhere.



Ah, that's better! All cleaned up with q-tips, Goof Off and alcohol, took about 2 hours.



Amazing it came out that clean, there was actually a nice looking transformer under it all.



Next I removed the bad sections of remaining wax and squared them off, using a soldering tool to melt it which was pretty smelly. Then I built a sort of cardboard trough around the remaining good section of wax tire, sealing the edges where it met the transformer with bits of wax. I poured 2-part silicone into this to make a mold.



Looks like it came out good, but how well had I captured the original profile? Pour in some wax to make a test casting! This is monocrystalline wax donated by John Yurkon, it matched the melt point and hardness of the original stuff pretty close but not the color.



Looks like a match!



Next step, position the mold carefully around the windings and pour:



The result looks pretty good.



Only thing is the original section of wax was slightly angled, and that transferred to the mold. That meant the new wax was slightly misaligned, as you can see where it meets the original wax. It's not bad enough to matter, I think this new tire will work just fine.

[NoPegs]

Originally Posted by miniman82

I poured 2-part silicone into this to make a mold.

Can you enlighten me on the specifics of the two-part silicone you used to do this? I have a whole list of things it would help me with.

[miniman82]

It was a kit from the hobby store specifically for making molds, it just happened to be a 2-part silicone. The name of it is alumilite quick set RTV silicone rubber, worked really good and the hot wax didn't phase it at all.

[zenithfan1]

Great job Nick! I looked this thing over at the ETF, I was amazed at how solid and heavy it is. I can't wait to see a picture on it

[Steve D.]

Nick may have mentioned this Gilfillan color prototype was from the late Ed Reitan's collection. I was in Ed's Los Angeles apt. helping with the moving of various items to the ETF when the movers wrapped up this behemoth and w/a dolly managed to get it down the many narrow steps from apt. to street, to moving van. The set does weigh every bit of 300 lbs. and is built like a bank vault. Ed managed to acquire the set when he worked for Gilfillan Corp. in their military radar division.

-Steve D.

[miniman82]

Thanks Steve, I intend to put up a video of this set playing those nice clips a few of the guys put together of his life. Should be a fitting tribute to our friend, and a nice way to cap off the restoration.

The HV cage is 90% reassembled now. The rewaxed flyback is installed, so are the rectifiers. Thanks to WISCOJIM for providing a new socket, to replace the one that had an ear broken off. All HV wiring has been replaced with 40kv stuff from Belden, hopefully there won't be any sizzling to deal with. I decided to replace the coin base GE brand rectifiers with period correct fat base RCA ones, now all the tubes in the cage (aside from the focus rectifier) are fat base T-12 style glass and it looks killer.

Last issue to deal with is the lack of a focus control. Right now there's just a bleeder network coming off the focus rectifier, a 3A2, with a tap after a few fixed resistors for the line to the CRT. There is around 15 megs of resistance to the string, which is more or less what the schematic calls out besides the fact that 5 megs of it is supposed to be in the control. Anyone have one of those special 5 meg focus pots they could donate? I've tried using a normal pot before (on my CT-100), but they always arc over.

Something like the one in the 621TS should work, but there are other sets using a similar style control.

[Steve D.]

Nick,

Your restoration looks to be a first class job. Ed would be very happy with your efforts. Those focus pots are not easy to locate. Steve K. replaced the pot in my CT-100 with the best substitute he could find. It has since failed. Also, as you know that particular pot has the longer shaft. I don't know if that is a requirement in the Gilfillan set. The Ed Reitan memorial tributes would be a fitting video to display on a set Ed Valued so highly.

-Steve D.

[miniman82]

Steve,


I know they can be tough to find, I may end up having to buy a donor chassis or something. Do the 8TS30 and 630 use the same pots? I can make a shaft extension if need be, won't be a problem.

[dieseljeep]

Originally Posted by miniman82

Steve,


I know they can be tough to find, I may end up having to buy a donor chassis or something. Do the 8TS30 and 630 use the same pots? I can make a shaft extension if need be, won't be a problem.

I find the 621TS, to be a rare bird, using electrostatic focus, high voltage at that.
All the other RCA's and clones, were magnetic focus.
Maybe a focus control from a 7" Motorola or other would be close. Maybe one of the centering controls. The secret is insulating them from the chassis.

[John Folsom]

Nick, another possibility is the focus pot from one of the late 11940s RCA projection sets; a 15meg 4 watt pot. I may have one if you think you want to try it.

[WISCOJIM]

Any luck with Mark Oppat "King of Controls"?

http://oldradioparts.net/controls.html

.