Admiral T102 scored

[bandersen]

I pulled the dual selenium AFC diode and tried to check it on a DMM and a VTVM. I got infinity on every range. I'd read these were tough to test. There seems to be some debate on what to replace them with as well: http://www.antiqueradios.com/forums/...c.php?t=110903

I just went with a couple 1N4007 because I have a bunch on hand. The horizontal sync is definitely more stable now. I'll poke around for some 1N914s too. I'm curioius to see if there's any difference.

The contrast and retrace lines seem better now as well.

Although the earlier screenshots I posted look good, the set and a tendency to either lose sync or drift off center like this.


Here it is with the new diodes installed Now, you have to really crank the hor. lock control way off center to lose sync.

[wa2ise]

Originally Posted by bandersen

I just went with a couple 1N4007 because I have a bunch on hand. The horizontal sync is definitely more stable now. I'll poke around for some 1N914s too. I'm curious to see if there's any difference.

I'd use any diode that is suitable to use as a AM radio detector diode. Rectifier diodes may be too slow (in time) to "recover" (start or stop conducting) and have too much stray capacitance. The set may have better sync stability even more, with the detector diodes.

I thought I posted last night about the domino shaped capacitors, some are mica (usually good) and some are paper caps (usually bad). Maybe I hit "cancel" or maybe my linking to another site's images was bad or wrong. Anyway, large uF class caps are usually paper, the pF class are usually mica. But horizontal circuits more likely use micas. Papers should be bad by now, so if the set works, they are probably micas.

[bandersen]

Originally Posted by wa2ise

I'd use any diode that is suitable to use as a AM radio detector diode. Rectifier diodes may be too slow (in time) to "recover" (start or stop conducting) and have too much stray capacitance. The set may have better sync stability even more, with the detector diodes.

I thought I posted last night about the domino shaped capacitors, some are mica (usually good) and some are paper caps (usually bad). Maybe I hit "cancel" or maybe my linking to another site's images was bad or wrong. Anyway, large uF class caps are usually paper, the pF class are usually mica. But horizontal circuits more likely use micas. Papers should be bad by now, so if the set works, they are probably micas.

There's about 20 volts p-p across the diodes so a 1N34A or 1N914 should be OK. I'll give both a try.

I also picked up a replacement 1N270 for the video detector. I haven't installed it yet though because it's a bit hard to get at.

[bandersen]

I poked around my local Menards for matching orange paint. This is what i came up with - Rust-oleum Engine Enamel Chevy Orange Red rated for 500F.
I hardly need paint rated for that temp, but it was the best color match.

Here's a test I did with a big iced tea can. Pretty good match I think.

[Electronic M]

My first tube TV was a GE 14T1- green and white two tone that someone replaced everything except the filters on. I paid 5$ for it and an EICO fly tester. It has great audio, but no HV. Once I dig it out of storage I'll debug the HV and possibly sell it, if I can't get HV I'll definitly sell it. In my bassackwards mind something has to work before it qualifies to sit on a shelf and go unused for months!

Tom C.

[bandersen]

Originally Posted by Electronic M

My first tube TV was a GE 14T1- green and white two tone that someone replaced everything except the filters on. I paid 5$ for it and an EICO fly tester. It has great audio, but no HV. Once I dig it out of storage I'll debug the HV and possibly sell it, if I can't get HV I'll definitly sell it. In my bassackwards mind something has to work before it qualifies to sit on a shelf and go unused for months!

Tom C.

LOL - That's what happens with most of my sets too.

[bandersen]

I polished the chrome carrying handle with Simichrome. It turned out well but now I can't touch it or I leave fingerprints


I noticed that this CRT like many of my others has some air bubbles in it. Not really noticeable unless you sit really close.

[wa2ise]

Originally Posted by bandersen

I also picked up a replacement 1N270 for the video detector. I haven't installed it yet though because it's a bit hard to get at.

The original is working fine, I'd leave it. You'd get no picture if it were bad. They don't go bad like seleniums do.

Sure that those air bubbles in the CRT screen glass are not vacuum bubbles?

[bandersen]

Originally Posted by wa2ise

The original is working fine, I'd leave it. You'd get no picture if it were bad. They don't go bad like seleniums do.

Sure that those air bubbles in the CRT screen glass are not vacuum bubbles?

LOL - could be. OK, I'll leave the detector diode alone.
BTW I did put small signal diodes in the AFC instead of 1N4007s and it's working even better now

[Tubejunke]

Originally Posted by Electronic M

In my bassackwards mind something has to work before it qualifies to sit on a shelf and go unused for months!

That is exactly the way I am! I (along with most of the women I have dated) have often wondered if it was some kind of mental condition that caused a person to have a drive to repair something just so it can sit on a shelf and get used once or twice a year in order to keep the capacitors in working order. Also, if I get stumped on something I seem to not want it around and the way things are now I am forced to go back in time and scrap it. I used to at least be able to give a TV set to someone, or better yet make a few bucks to make back some of the cost of replacement parts and the value of tubes. After NOT being able to find a loving home for my 1958 24" Zenith Space Command console set, neither for money or for FREE, I am just going to scrap anything that is not simply extremely rare. I had high hopes for the Zenith due to what seems to be a VERY low use chassis and crt and the fact that the 24" tube is not exactly common, nor was remote control at the time.

[bandersen]

I buffed out the safety plastic with some Novus. There are still a couple deeper abrasions but it's a lot better than it was.

The picture has never been particularly bright, but I figured that was just due to the age of the picture tube. Well, I was about to put it together when I decided to check the HV with my Pomona probe.
It's only 6 kV when it should be about 7.5 kV. I also did a dry run an discovered I can't get the vertical to fill the whole visible screen. I guess I have a little more work left

[teevee]

Yes, I repaired the defective ballast in my VT-71 with a pair of AC rated capacitors (plus 2 resistors), and it works well, and runs cool. As I recall, I think the caps were 8.2uF for this set. Have to verify that when I get back in the set..

[Tubejunke]

Have you checked the B+? Just curious if it were possible for that being low to cause lack of vertical size and lowered HV at the second anode.

[Eric H]

Please don't scrap your Zenith, someone will eventually come along and get it running for you or buy it.

I'd love to have a look at it but I'm too far away!

[bandersen]

Originally Posted by Tubejunke

Have you checked the B+? Just curious if it were possible for that being low to cause lack of vertical size and lowered HV at the second anode.

Yes, it's dead on. If I vary it using a variac, the vertical and HV don't change much. I hope it's just a matter of some resisters being off.