Resistor or jumper at hv rectifer socket: Zenith 25mc30

[dieseljeep]

Originally Posted by Tubejunke

So if I leave it (killer) on and when everything is as it should be, the snow will more or less go away. I had assumed that not to be the case and setting it too high would be about like setting AGC too high. I fully admit more or less being fairly new to troubleshooting vintage color television beyond that of normal static convergence and other setup procedures.

This is the only vintage color set in my ever smaller TV collection (due to space and sanity). My primary interests have always been in earlier black and white sets and radios. I have owned a number of round tube color sets back when they were available very cheap and made great daily use sets. So bringing one back from decades of dormancy is new to me.

Thank God for the incredible pool of great people and knowledge here at VK to pass along what I as an electronics professional consider a lost art in the field that will vanish if not somehow kept alive. These days there are 'techs' who can barely read a meter; and I mean DIGITAL! They could care less about Ohm's Law, Kirchoff's Law,etc. To avoid a rant I will end this now as I must or that is what it will become.

You mean to say, they don't know Thevenin and Norton's theorem either?
I'd have to get back to the books! It's been years.

[Tubejunke]

Originally Posted by dieseljeep

You mean to say, they don't know Thevenin and Norton's theorem either?
I'd have to get back to the books! It's been years.

No they don't. Ohm's law would be the only thing that a modern JR college curriculum would include and perhaps Kirchoff's Law; and that would be very limited. I don't mean to put the younger techs down for what they were never taught. I just think that it's a shame that what was once a respectable discipline that was pretty darned involved and anchored in the roots of the science of electricity/electronics has like so many things been dumbed down so, yet the students attain the same credential as students of old who I feel had to work harder to get what they got.

I have been told that my mindset on this suggests that I or anyone else should attend a university. I say that's wrong because you are not going to perhaps get through a high school trades course and then get a couple of years of college under your belt to find yourself beginning the theories and the math to prove them which is the foundation for all of what we do when completing your Bachelor degree which at that point would be electrical engineering. I guess there are better and worse JR college programs and a lot of what I remember was a bit of a joke. And that's back when it was a lot harder than today.

I remember an exam question on the definition of voltage. The correct written answer was "a force." Sure, it's a force. So was a big part of Star Wars! Just an example. I am told now that they have almost completely converted the focus to what is known a Mechatronics. Basically automation, so some factory can get you to be the grease monkey and the electronics tech. The I.T. guy gets an office! So the college tossed a truckload of oscilloscopes, function generators, Variacs and other great tools in the dumpster one day. You couldn't even buy them as they were government property to be destroyed. I won't bother going into grading most tests based on the lowest grade so basically nobody flunks out. Money!!!

[Tubejunke]

OK folks, as promised; here is where I stand. I didn't want to post pics until I had a decent color picture. I think I found and tested 10 6GH8 tubes before I found one even marginal one one of the two tests for that tube. The rest were LOW emissions. I have heard that the 6GH8s were lousy tubes and my B & K Dynajet 747B sure proves that. I notice that there are some common subs like 6U8 and 6EA8 that may work, but I had none on hand. Anyone every tried any other subs?

But as for the whole HV rectifier project; it looks like a wrap. Very stable and still using a slightly reduced line voltage I can maintain less than 200mA at the horizontal output's cathode. The fly seems to be running cooler than it was when I had the old socket and corona hiss. I absolutely love that silence and a cool fly.

I am really surprised at the generally good color picture with really no alignment. Not proper anyway. I did set the service switch and touch up the guns to get as good a white line as I could, but there really wasn't much to do there. Next comes the use of the same age RCA dot bar generator as up close there are obvious alignment issues. I think it will be stunning when I work those out.

Thanks again everyone for the help on this!

Tube

[Electronic M]

Lookin' good!

[old_coot88]

Good job!

Heck, I learnt sumpthin' too.. the resistance wire used for the 3AT2 filament.

[Zenith6S321]

Nice work.

[Tubejunke]

Thanks to Electrronic M, Zenith6S321 & Old_coot88 for the kind words. I tell ya; one thing about messing with old TVs (especially color) is that there is always a new mystery or maybe some adjustments around the corner. The lovely pic of Ray Charles was actually taken with the set on it's side for service next to (of all things) my Frigidaire.

So, I'm finally ready to set her down for normal viewing and powered her up; color gone. And my black and white wasn't so black and white anymore. The intermittent color I deeply feel is that darned 6GH8 Chroma Reference Oscillator that I mentioned in an earlier post. What is up with these 6GH8s?!?!? Anyway, I think the rest of my impurity is a magnetized C.R.T. or simple purity adjustment as I had moved the rings some while it was on it's side.

[Electronic M]

I may be able to dig a couple of healthy 6GH8s out of my tube stock for you if you need them.

[Zenith6S321]

When I first started on my 29JC20, the color would work but then quickly fade away as it warmed up. Is that what you see, or is there no color when its powered up cold?

[DavGoodlin]

Originally Posted by Electronic M

I may be able to dig a couple of healthy 6GH8s out of my tube stock for you if you need them.

Make sure you test any used with something like a B&K 747. I have so many tubes from Zeniths, I sent Greg a variety of tubes for his set that tested great on my emission tester and they failed on his. Since I now have three of these Zeniths, Im really paying attention so I can maybe solve some of these riddles for the benefit of all.

[Electronic M]

Anything octal/loctal or newer I test on a B&K 606 (it works good so it is all I use where applicable).

[Tubejunke]

Originally Posted by Electronic M

I may be able to dig a couple of healthy 6GH8s out of my tube stock for you if you need them.

That would be cool; really cool. Even one good one would be nice. Also, as it was brought up, I use a B & K Dynajet 747B these days for the most part or sometimes a Hickok 6000A, so I have little fear of mis-testing. I have seen it on a plain emissions tester that I have by Accurate Instrument Co. Almost all tubes test good. Weird!

Also, I found a bad 6KT8 last night and sort of ended up in the same situation with a bunch of bad ones. Several were the ones that Dave sent me and a few were my own. I have one more box to check for others, but may need one of those if plentiful. Let me know what you find Electronic M. Thanks!

[Tubejunke]

Originally Posted by Zenith6S321

When I first started on my 29JC20, the color would work but then quickly fade away as it warmed up. Is that what you see, or is there no color when its powered up cold?

No, I don't see the former, but I do see the later. My set often (more than not) starts off in pure black and white with the exception of impurities now that my Frigidaire magnetized my tube or possibly other adjustments like purity rings need to be adjusted. Anyway, no color until after quite a bit of warm up. Maybe 20 minutes or so. Once it's there, then it's there to stay normally till I shut her down.

As previously mentioned, I am working with more than one marginal at best tube in the color circuits. That may be the whole thing. I hope so because I want to get this thing stabilized and get my same vintage RCA color dot bar generator hooked up and do her up right!

[Zenith6S321]

(Edited cause I forgot this is not a 29JC20!)

It still could be an effect of the Zenith automatic control control/color killer that caused my color fading issue. One way to see if that's it is to disable the color killer. If your color comes back then its not the 3.58 MHz oscillator that is causing the problem.
Dave

[Tubejunke]

That sounds like a good idea. I will keep it in mind. Tonight I powered it up and it almost seemed like color wasn't going to come in. I started tweaking the killer and the tint and the color just came in. I REALLY need to get into some purity and static convergence when I get stronger tubes in there. I tested my 6KT8s on my Hickok and the Accurate Instruments for comparison. All good on the Accurate and all weak on the Pentode test with two having marginal triode tests. I used the stronger one of course. I think that the color takes so long to come in due to the marginal emission and a usually reduced line voltage causing slower. I have noticed that I can bump up the line voltage and shortly thereafter the color will come in; then I can back off to ensure the 200mA horizontal output cathode current and the color will remain.

Question: When I am setting up my convergence clover, is the black line on the crt's gun an index as to where the plastic edge of the clover should go to have it directly over the beam converging pole pieces? Some of this has been moved and I want to have it dead on so I can slide the yoke back and work my purity rings for a red center; then move the yoke back till I achieve the best red screen possible. This of course with the other two guns extinguished.