Sylvania 1-076 arrived!

[jeyurkon]

Originally Posted by John Marinello

Why would you have to shim the yoke? Can't you slide it up snug against the bell of the CRT?
Your picture is really looking good!

The yoke sits in a half tube that has a slot. A thumbscrew goes through the slot to allow you to rotate the yoke. The nut that the thumbscrew goes into can slide along the length of the yoke. Once in position you're supposed to tighten the thumbscrew. If you don't it doesn't stay in position. The problem is that when I tighten the thumbscrew the front of the yoke is too low and the rear is just a tad too high.



The half tube in the early sets had slots to allow you to adjust it's position. In later production they just spot welded it into place. I guess the replacement yoke doesn't match the physical shape of the original yokes well enough. The slots are still there. I could drill out the spot welds and add the adjustment, but I rather just shim the yoke between it and the half tube.


John

[jeyurkon]

I read in an RCA TV servicing guide that the trapezoidal raster that I had would be caused by a problem with the vertical portion of the yoke. I don't understand that, I really thought it would be the horizontal, but decided to check it out.

In order to ring test the sections properly I have to remove the core. I started to do that, but after removing the damping resistors for the vertical windings I decided to check them. They are supposed to be 560 ohms each. They are 680 ohms and 725 ohms. I think that's enough to cause a problem and I should have checked that before swapping the yokes.

I'm trying to decide whether to replace the resistors and reassemble the yoke, or to continue the testing. I'd have to unwind a lot of iron wire and rewind it carefully later. To check the coils individually it's necessary to reduce the mutual inductance by removing the core. However, the vertical and horizontal shouldn't have much coupling. I ring tested both and got 9 rings each. There might not be a short and the real problem could have been due to the bad damping resistors.

In either case, I'm not going to put it back in this set since Sylvania says that this model yoke shouldn't be used with the horizontal choke that is in the set because of danger of breakdown.

John

[bandersen]

I wonder if you could use an Eico 944 Yoke tester on it ? Supposedly they can detect a single short.

[jeyurkon]

Originally Posted by bandersen

I wonder if you could use an Eico 944 Yoke tester on it ? Supposedly they can detect a single short.

It would be interesting to try, but I think they'd give the same result. I took a quick look at the manual for the Eico. Both the Eico and the Sencore LC101 test the yoke by measuring the absorbed energy, though by different means, and are sensitive to a 1 turn short. The Sencore does it by forming a resonant tank circuit and pinging it. It then counts the number of oscillations to decay a certain fraction.

The problem is that with an iron wire core the Q is low and the energy absorbed is higher. The results I get with the Sencore are right at the border line. The Eico manual also indicates that you can run into this problem, and in that case you want to compare the reading with an identical yoke. The replacement yoke I have isn't identical, it has a powdered iron or ferrite core which gives you a higher Q.

If I remove the iron wire, then either unit should give me an unambiguous result since the Q should be quite high.

John

[jeyurkon]

I finally got around to doing more work on the cabinet. It's difficult for me since I expect everything to be square and all measurements to be a multiple of a rational number.

I replace the missing support rails and made a new base for the chassis. The square hole on the left is for the speaker cable. The oblong hole on the right is for the AM antenna wire. The small square opening is to access the adjustments that don't need frequent access. I was forbidden to touch these as a kid.

There was another hole that could only have been used to adjust the tension on the CRT strap. I don't understand why they put it there since you have to remove the chassis to remove the CRT.

Maybe they wanted to be able to re-tension the strap before shipment, after the rubber pads conformed, or perhaps make it easy for the installer to raise the base end back up if it got shaken down during shipping.

John

[ohohyodafarted]

Shit John,

If you keep doing work that looks this good, my stuff is going to start looking shabby in comparison

Bob

[jeyurkon]

I made a mount for the speaker. I suppose there's a technical name for it.

I attached a grille cloth. The proper grill cloth would have had a similar pattern, but much darker brown. Almost charcoal grey with silver thread running through it.

There seems to be a stain on the cloth. I noticed it when I went to iron it. I think it's oil or sweat. When I placed the first order for the cloth they sent me a 1'x2' piece when I ordered and paid for a 2'x2' piece. I think next time I'll order it from the place that specializes in vintage grille cloth. I suspect they put more care into it.

There's some stain, water based I hope, that I have to clean off of the finish. This was from when my dad converted the cabinet to a linen cabinet and lined it with cedar. He had to add some rails and stained them to match. There's a few holes to fill also.

I have to make some round corner molding to finish the installation of the speaker.

John

[wa2ise]

You may want to, if you haven't already, paint the light tan colored plywood mount for the speaker black, so it isn't visible thru the grill cloth.

[jeyurkon]

Good idea, but I already glued the speaker cloth on. It won't show up much under normal lighting. It's pretty much shaded since it's recessed from the front by about 13". A camera with a flash always makes it look worse.

If I end up redoing it I'll paint it as you suggested. I'm not real happy with how I distorted the fabric. Next time if I use a lightweight fabric I'll make up a clamp to stretch it rather than trying to use gorilla tape.

Oddly enough gorilla tape didn't want to stick to the fabric.

John

[jeyurkon]

Odd, the area that looks like it has a stain doesn't look that way anymore. I used steam to press it but I would have thought that would evaporate quickly.

John

[jeyurkon]

Well, I guess the stains are still there, they just don't show up except when you take a photo. The same with the speaker cutout. I should have painted it a dark color, but it doesn't show up under diffuse lighting. I said the speaker was recessed 13". Not sure what I was drinking, it's more like 5-1/2".

I made corner molding out of mahogany using a 1/4" round-over bit with a router and table saw. I still need to varnish them and nail them in.

John

[jeyurkon]

I put a finish on the molding and installed it. That's a little difficult since it's only 1/4" wide. I wasn't able to come up with a filler for the brads that match the finish very well.

The color of the grille cloth seems too light. In looking at the photo on the front of the Sams I'm not sure it was a diamond pattern.

I remember it being nearly black, my brother says it was dark brown with silver running though it.

AES has a black and a brown basket weave pattern for guitars that looks pretty close. I'll order some samples and see if I like it. If I do, I'll probably change the grille cloth.

Looks like my work was kind of clumsy on this one.







John

[jeyurkon]

I finally finished up the panel. I started by laminating ribbon cut mahogany paper backed veneer on to plywood. I veneered both sides to prevent it from bowing later. I used Heat Lock glue.



I then made a paper template.



After transferring the template I cut out the panel.



Then I checked the fit.



I then filled the grain by padding on six coats of orange shellac. Sanding it down to the wood with 180 grit sandpaper. Then repeated, but just sanding down almost to the wood. 180 grit is too coarse. I used it after reading a procedure on a woodworking site. I ended up using 600 grit for sanding between coats of Lacquer. I used Mohawk Classic Brown Mahogany.

The front after apply several coats of the toner lacquer and a couple of coats of clear satin.





And the back with clips installed.



In order to screw it in with wood screws as it was originally done I had to make a fixture for my drill press to angle the screws 30 degrees from the normal. I glued on cork so that it wouldn't affect the finish. I couldn't just free hand it because the panel sits behind strips that are only 3/16" thick and you don't want to risk having the screw hole show up.

It was either this or make a drill guide to hold in place inside of the cabinet and use a hand drill.

The fixture:



Here's the final product. I'll have to take some photos of it working. The bezel is NOS courtesy of rdreyfoos. It has a little shop rash on one corner, but I'm reluctant to try to repaint it at this time.



As I mentioned previously, I don't want to refinish the rest of the cabinet for sentimental reasons so I had to try to match the finish.

John

[bandersen]

Wow!! Fantastic job

How did you cut out the panel ? It looks very clean and crisp.
I'm a little surprised how red that toner turned out. I'll keep that in mind for future projects.

[jeyurkon]

Originally Posted by bandersen

Wow!! Fantastic job

How did you cut out the panel ? It looks very clean and crisp.
I'm a little surprised how red that toner turned out. I'll keep that in mind for future projects.

The round holes were drilled with Forstner bits. The large opening and the square hole were cut with a scroll saw. I then made a jig with a rectangular opening and used a laminate trimmer in a router to clean up the square hole.

I then used the router on the table saw's router table to clean up the straight sections of the CRT bezel hole. I had to touch up a couple of places on the curved sections by hand with the router.

It did come out pretty red, but the red was accentuated in the outside photo because the sun was setting on the horizon.

John