Sylvania 1-076 arrived!

[jeyurkon]

I'm torn between rewinding the coil and repairing it. It has 16 turns and is bifilar wound. Should be easy enough to rewind, but just as easy to fix. Both ends are open. One end I can just reattach to the terminal, the other end I would need to splice.

I had to soak it in lacquer thinner. That didn't dissolve the alkyd coating but softened it enough to scrape off.

Any suggestions as to which route I should take?

There are only two components that could have caused the failure. Other than someone twisting the form while trying to adjust it.

One would be the tube which tested o.k. At least not shorted. The other is a 0.68 pF 500V axial ceramic. It's too small a value for me to test, but the leakage at 500V is less than 100 nA. There's a 0.005uF disc ceramic on the secondary that has 1.2uA leakage at 500V. That didn't cause any problems though. I'll replace it anyhow since it's really ugly looking.

The color code on the 0.68pF ceramic is Blue-Gray-Silver-Nothing. I'm not familiar with this coding. Anyone have a chart for this type of ceramic cap?

John

[kvflyer]

Yes, it looks good. I can understand your desire to keep the selenium rectifiers. But, they will be a pain from this day forward. If you are looking for originality, you can hide a 1N4007 behind that selenium I am sure. Just a thought...

[John Folsom]

John,

Nice job on the IF transformer. Here is a link to capacitor color codes, hope it will help:
http://www.tpub.com/neets/book2/3g.htm

[jeyurkon]

Originally Posted by John Folsom

John,

Nice job on the IF transformer. Here is a link to capacitor color codes, hope it will help:
http://www.tpub.com/neets/book2/3g.htm

Thanks for the compliment and the link. The axial ceramic cap color code table is close. But, like all of the others I've looked at they don't include silver in the multiplier. I guess I should just assume it follows form since that gives the schematic value.

John

[jeyurkon]

I think I've found the problem with the horizontal circuit. The symptom is that it's only stable with the blanking bar down the center of the screen.

I don't fully understand the circuit. It's a sine wave type horizontal AFC.

But suffice it to say that the output of the sync clipper is fed to the horizontal discriminator through a 100pF capacitor. It was supposed to be an axial ceramic. It's actually a Micamold.

All the bad things I've heard about micamolds are justified. If a capacitor can be evil, this one is. The discriminator circuit requires it to not have any leakage. It has about 16 uA at rated voltage. But it gets weirder. The capacitor testing gives up trying to measure the value if the cap's been resting for a long time. After measuring the leakage, the capacitance tests out at 300 pF. It then gradually ramps up to 3,000 pF after a few minutes of testing.

At least this one is easy to get to. The other one that I'll replace is used to turn the line cord into an FM antenna. Given that it would probably burn my house down I'm inclined to replace it.

I wish the 13 others weren't so difficult to get to; I'd love to replace them but since they seem to be working I guess I'll replace them when their time comes.

John

[jeyurkon]

Finally!

I changed the micamold and found two caps I had switched. A 0.005 and a 0.010 uF. There's one micamold left that is for the horizontal ringing coil. It's hard to get to, but I should change it.

Here are some photos. Is this the typical linearity that you should expect for a set of this vintage?

John

[dreyfoos]

John, those photos represent outstanding work on your part. Congratulations on getting that old babe back to as good as, or even better than, new.

As to linearity, looks to me like you're down to the point where any deviation may only be in the eye of the beholder.

Three cheers for a job well done! And thanks for sharing all the details with us.

Roger

[Tony V]

Awesome!
-Tony

[jeyurkon]

While doing some fine tuning of the set I realized that the Zenith Wavemagnet I picked up has the right inductance to use as a loop for the AM section of this set. I tried it without doing any alignment and the reception was amazing.

This might be pretty good for AM DXing.

John

[jeyurkon]

I need some advice on dealing with a problem with the volume control on this set. It's a 1 meg composition pot tapped at 500K and 250K. It has a hollow shaft. The Photofact doesn't list any replacements other than Sylvania so it's pretty much going to be impossible to find.

The resistance from one end to the other is 1.2 Meg, which isn't so bad. The Symptom is that the volume jumps up to a loud leve when I start turning it up.

I've attached a scan of this section.

It seems that a spot was burned in the conductive film near the bottom of the pot. Possibly when paper cap C25 was leaky. As you go past this spot the resistance measured at the wiper jumps from 25 ohms to 250 ohms. If I measure the resistance to ground from the other taps they jump down to the correct value when the wiper is in the center of this spot. I imagine the conductive trace having a burned spot in the center of the trace, but good on both sides. I've attached a sketch of what I think it might look like.

I think the taps are there to keep the tone the same as the volume is changed. I could just short the 250K tap to ground. I'd lose a portion of the range. The tone might sound a little different. This would be the easiest solution.

I could try coating the spot with aquadag to cover the burned spot. If it's small enough, it might not be noticiable.

To get at it I have to remove the CRT, the front panel, and the plate that holds the pulley for the dial cord. I hope to avoid that.

Any other suggestions on how to attack this problem?

John

[jeyurkon]

Well, the problem with the volume control wasn't what I thought it was, and the problem was fixed by an unfortunate accident.

Instead of a burned spot on the resistive trace, it was where the terminal on the ground side was riveted to the phenolic board with the resistive trace. I didn't notice that a tubular capacitor that is on the end of a coax running to the wiper of the volume control was too close to a resistor. It arced through the paint on the capacitor while I was watching and made violent discharges in the volume control. I expected the worst. But, it turns out it just improved the connection so now the volume control tests and works perfectly!

John

[jeyurkon]

While I was able to adjust the set to give a good picture, there was still a problem with the horizontal. I wasn't able to adjust it according to the service literature. Basically you're supposed to remove the discriminator tube, the 6AL5, adjust the frequency until the bar moves slowly across the screen and reinsert the tube. It should lock in at this point and then you adjust the phase.

They then have test the pull-in range by adjusting the frequency CCW until it unlocks, then adjust it back slowly until it locks in and you count the number of bars just before it locks in. Then CW and count the bars. They're supposed to be between 3-4 bars in both cases. In my case when I turned it one way it would just slowly drift across. In the other direction it wouldn't unlock until I made many turns.

I also wasn't able to adjust the phase independently.

I checked all the caps and resistors. I replaced the micas. Nothing helped. I started to suspect the horizontal oscillator transformer. But, I noticed that the DC level on the grid of the 6AU6 control tube was -1V when it should have been -3V. The 6AU6 is used as a reactance tube to control the frequency based on the output of the phase discriminator. -1V put it at one end of it's control range so it could only adjust the frequency in one direction if the free running frequency was set correctly.

The bias is determined by dividing down the -125V supply. First they divide it down to -30V with a low impedance divider then down to -3 with a 10meg and 1meg in series. I checked those and they were o.k. I was getting close to modifying it to give the right bias when I decided to swap the 6AU6 even though it tested as new and seemed to work. Well the bias went to -3V with the new tube and I was able to align the horizontal sweep as per the service manual. The grid on the 6AU6 was drawing 0.2 microamps at -1volt. My tube tester isn't going to notice that.

Now the only problem I have is with the FM. Although it worked great in the beginning, it is now fading out after 4 minutes. It runs for 4 minutes after turning on and then suddenly the volume drops.

I've replaced two micamold caps. One was leaky, the other was o.k. Some resistors are out of spec, but I don't think they're at fault.

What is curious is that the AM function works fine even when the FM has dropped in volume. They both use the same circuitry except different IF transformers and osc frequency. There must be a clue in this.

You can see the schematic for the radio section on the last page of:

https://www.msu.edu/~yurkon/Sylvania_9-2_Sup1.pdf

This is getting to be really frustrating. I swapped all the tubes in the radio after my experience with the horizontal 6AU6 but it didn't make a difference. Any suggestions for what to look for would be welcome.

I'd like to get it off my bench so I can work on my alignment generator and get it working. I want to touch up the alignment since I had to rewind one of the video IF transformers.

I'm also working on making a bezel for the 12" version of this set. A friend drew a mold up for me based on my measurements. I didn't notice however that the had made the face a cylinder instead of a sphere. It wasn't obvious in the preview. It became obvious when the shop I'm using tested their programming on a shape board.

If I'm able to cast a 12" bezel then I'll put a 12LP4 into the chassis. It should really be a 12VP4 but I'm unlikely to find one of those. I'll have to add a screen bias supply. One of the 16" Sylvania shows a circuit to do that, based on this power supply.

This is basically changing it from a 1-076 model to a 1-128 model. I have the cabinet from my family's 1-128, just nothing is left of the electronics. The 1-108 chassis was used in both. If I can't successfully cast a bezel I'll refinish the 1-076 cabinet and stick with it.

John

[Tube TV]

John , you have done a great job .
Such a neat set to restore .
If you ever need a volume control , I "might" have one .
I've got a big box of different ones that were salvaged by a TV / radio guy back in the day.....

[jeyurkon]

Originally Posted by Tube TV

John , you have done a great job .
Such a neat set to restore .
If you ever need a volume control , I "might" have one .
I've got a big box of different ones that were salvaged by a TV / radio guy back in the day.....

Thanks for the offer. So far the accidental repair by loud sparks is still going strong. I just couldn't believe my luck. I thought for sure I would have destroyed something.

John

[jeyurkon]

Since I won't have the set back in a cabinet by the time analog TV is history, I thought I should shoot a couple of photos of over the air broadcasts.

The on the left is Channel 12 in Flint Michigan, 36.1 miles away. The one on the right is Channel 6 in Lansing about 7.4 miles away. For channel 6 I don't even need a rabbit ear. Just 2" of wire.

The key-stoning you see in the right hand photo is because I'm close to the TV and at a slight angle.

I think the slight fuzziness is because I need to align the video IF. I have to finish restoring my Hickok alignment generator first.

I've also been slow in starting on the cabinet because I've been tracking down all the minor problems I could find. One was a crackling in the sound as the set warmed up. I thought I'd find that one of the electrolytics that I decided to keep was failing and I'd have to swallow my pride.

It turned out to be the 6Y6G audio output tube. I swapped it and the crackling went away. Swallowing my pride will come later.

I wonder if there is a heater to cathode short developing with it. The tube is coated so I don't think it was secondary emission from the glass.

John