I have an important question

[Bill Cahill]

That's the way I kind of feel. In the past I've given up on things, stripped, them, then, found the reason they wouldn't work.
But, this set has certainly been a tough dog....I guess I'll just have to keep pushing along.....
Bill Cahil

[pugs5061]

Bill I have to say you have been an inspiration to this newbie. Not only have your posts on ARF been informative for me but without them, I would be up a creek without a paddle sort a speak. I'm trying to get a 1950 RCA TA129 going(very similar set) and have never even attempted anything remotely this complicated in the vintage electronics arena. I have started running into alot of the problems you have run into and right now I am fighting a lack of resistance on my 5U4 tubes. I am assuming its a short somewhere down the line and not a transformer because this is an intermittent thing. Just knowing the tenacity that you have shown on your set keeps me fighting to keep going as well. I know its not a democracy but my vote is to tough this thing out and "Get R Done". I know if you can finish it up, I will also. Even if you eventually do figure to give this thing up your actions so far will still keep me persevering on my own project.
Perhaps a search throughout the country for the same set and finding it may give you the ability to finish this off with the least amount of pain. Perhaps having a "parts" set sitting next to you to compare, switch out parts etc. etc. would be an option. I know you are on a fixed income but if this is something you'd like to pursue I'm sure with the help of this forum and ARF we could make it work for you. Count me in for sure.
Again thank you for being so dang stubborn, its inspirational to us all.

[Bill Cahill]

Here is one thing you can do.... making sure where everything connects first, one at a time, disconnect B+ feeder line from each major circuit until you have found the shorted area. When resistance goes up, then, you have found the circuit with the short.
That's what I had to do alot of.
The set you are on isn't like mine.
Yours has floating B-, and, +90 volts going to chassis.
That is part of the negative bias.
The KCS 47, which is mine, is a much simplified version.
Do you have the schematic on yours?
I know it's in RCA, and, may also be in Sam's. I know it's definately in Ryder's.
Thanks. I've been under the weather today, so, have been in bed alot.
Hopefully by next week, I'll be better, and, back on the set.
Bill Cahill

[Reece]

Not to hijack Bill's thread, but Pugs, if your set has (especially) wafer type tube sockets, sometimes arcing can occur between the two layers and the resulting carbonization can cause a short, especially in rectifier or other high power tubes. The fix is to replace the socket with a molded type, or ceramic, even better. Worth a look.

[pugs5061]

Thanx for the tips! My mistake on the similiarities in our sets. Yes I do have the schematic and it has helped immensly. I have done some of the B+ ellimination but it is time to do it in earnest. I will definitely keep in mind the possibility of arcing but being so new to this I'll still bet it was a screwup on my part when replacing caps or a bad solder joint.

[Bill Cahill]

I've found the problem!
I've FOUND the problem!!
Almost positive, anyway....

I had a brand new old stock GE 12AU7 in video socket.
At the time, it checked per fect!
I tested it again tonight. One section was DEAD!
I then checked the one I had tried in set. Same section was DEAD.
I checked two others, and, they tested good, both sections.
So, I went to put good tube in video socket.
Guess what I found!
A broken tube pin in socket.
The other tube had broken the pin when I installed the tube, never had that happen before.
New GE? Maybe an open cathode?
I'm going to check other tubes to be on safe side, again. Then, I'll put the set back together, and, try it out.
Wish me good luck.
Bill Cahill

[DaveWM]

good luck, hope it works out.

[Bill Cahill]

I really believe this should fix my video problem. Then, I can get back to adjustments....
Thanks...
Bill Cahill

[Bill Cahill]

Haven't been able to get back on set to finnish checking tubes tonight. However, it looks prommissing...
Bill Cahill

[Bill Cahill]

Just finnished checking some other tubes. I had a weak 6AU6 2nd video I F tube. Quite weak.
It's gone.
Well, it was used.....
Anyway, when I'm next on it, a little chassis neatenning, then, I put it back together, and, try it.
It's gotten dusty on top, and, I want to do a minor cleanning.
Also, one of my pix tube wires is too long, and, I wish to shorten it slightly.
Bill Cahill

[Bill Cahill]

It's a NO Go!
Tried set today. Still no go.
Just a raster, and, now, I notice sound is a little weak, and, has some hiss.
Is problem in I F's, or agc circuit???
I'm at a loss........

Bill Cahill

[Sandy G]

I wish I knew enuff about this stuff to offer a suggestion....Or I could come to yr QTH & stand there, wring my hands, knock my knees together, bite my fingernails, moan, "Oh, woe is me !" & do yr worrying for you...(grin)

[jeyurkon]

I don't have a schematic for your set, but if it's like the 6T72 then it could be anything from the 3rd video IF on. I don't think it would be an AGC issue.

But, maybe it's something really simple. It looks like you could still have a raster and no effect from the contrast control if the CRT socket was making a bad connection to G1 of the CRT. That would be the video output line. I'd check for that. It could even be a problem with that pin of the CRT needing re-soldered.

Since you had a broken pin in the the socket of the video output tube, 12AU7, then there's a chance that the socket was damaged, perhaps that socket was spread wide and isn't making good contact now.

Try measuring the DC level of the video output going to the CRT. On the wire going to the CRT it should be a negative value. On the 6T72 it appears it would be -1.8VDC.

John

[jr_tech]

For grins, I scanned in the video output circuit of the KCS47A... hope it shows up ok. Contrast control is on the 1st video amp, Plus it has a Dc restore/AGC/Sync separator on the video output.
jr

[Bill Cahill]

Thank you both very much. Your ideas and, from my friend Mr. Detrola at ARF
coincide, and, give me an excellent starting point on what to do.
As soon as possible, I ntend to impliment those ideas.
I'll let you know the results.
INterestingly, the agc switch is also having no affect, so, that shows that for some reason, the signal just plain isn't getting to the picture tube.

I have a further question...
I checked the tube on my BK 465 tester, and, it says tube is wonderful!
Would it still check good if that grid wasn't making connection?
Not sure where the tester gets its' data. Cathode, grid, or, what?
Bill Cahill