1950 RCA 16" 6T65 (KCS47 chassis) repairs and alignment - Videokarma.org TV - Video

Adam · #1 11-04-2009, 01:10 PM

I picked this set up a few years ago. Did the usual recap. First sign that something was weird was the missing "doorknob" HV filter cap. The only replacement I could find was 30Kv and required I enlarge the hole it fits in, but that wasn't much of a problem. I try it out, but I get no HV and the 6W4 damper and 5U4 rectifier both light up like christmas trees inside. Next I start checking the yoke and flyback, and notice someone stuck both in here from another set that don't belong. This is when I also notice that the horiz hold control is open in most positions. And while I was poking around I also replaced a few more than 10% off resistors in the horiz sync circuit (but none were way off). Then, I get replacements for the horiz control, yoke, and fly and try it out again, but I still have the same problem. The trouble turns out to be in the power transformer itself, the damper filament winding shorting to one of the other secondaries. I briefly get the set to come up (with a blank raster only) using a separate filament transformer for the 6W4. But then something else in the transformer shorts for good.

Now I've replaced the power transformer, and switched the damper tube to a 6AX4GTB. Then I had a blank raster, no picture / no sound.

Then I adjusted the local oscillator going from ch 13 down, with the frequency counter, setting each for 21.5MC over the frequency of the channel. Then I had picture, and really bad sound (quiet with lots of buzzing).

I aligned the sound IF and detector transformer following a procedure in the sams with a signal generator set to 21MC into the control grid of the sound IF tube. This worked, but there was still some buzzing, and the picture didn't quite line up with the sound in the fine tuning. So I repeated the alignment with the tv receiving a signal on ch3 with the fine tuning set to best picture. Now the sound is good, with minimal buzzing.

But the sound still causes interference in the picture, horizontal bars across the screen increasing in intensity with that of the sound.

So now I want to try a complete re-alignment of the IF, both sound and video, partially because I think it will fix this, but partially just because I've always wanted to learn to do it.

So I have my sweep generator (RCA WR59B), television calibrator (RCA WR39C), and marker adder (RCA WR70A). They are all in very good and clean condition, and I have the manuals that came with all 3, and the cables and probes from the WR59B and WR39C, but not the WR70A. First I'm going to recap (paper and electrolytics) my equipment and make sure it is in working order. I'm ordering the caps I don't have now.

*Bill Cahill* · #2 11-06-2009, 10:11 PM

Best of luck to you. Please post in ARF, also.
Bill Cahill

Adam · #3 11-14-2009, 12:43 PM

I got my caps today. First up is the recap of the sweep generator. Here's some pics.

Adam · #4 12-04-2009, 11:48 AM

I'm half-way there. The sweep gen is recapped and working now (tested it with a scope and frequency counter). I'm considering trying it out hooked to the set before I fix the marker generator, just to see how well it really works.

John Folsom · #5 12-05-2009, 11:57 PM

If the sound bars in the picture change with volume setting, it does not sound like an IF alignment problem. If you remove the audio amp tube and the sound bars go away, it is probably not an IF issue. If they do not go away, it is alignment or filtering in the IF stages or or tuner. Another possibility is a micropnonic tube.

Adam · #6 12-12-2009, 01:04 AM

The volume setting has no effect. I just mean the bars correspond to the sound.

I finished recapping and repairing the marker generator now too, almost ready to try the alignment.

*Bill Cahill* · #7 12-12-2009, 02:12 AM

To me this doesn't sound like an alignment issue. Sounds more serious.
Wish you'd take pictures of it playing, Pictures can mean much more than words.
I've been working on tv's for a long time, and, have alot of hard learned experience with the KCS 47.. Sounds like something else is going on.....
Have you totally re capped it, including in the hv cage?
What type of sound are you getting?
What is your picture tube displaying for a picture?
These sets, while good performers, have their quirks...
Bill Cahill

Adam · #8 12-12-2009, 10:40 AM

At first there was no sound and buzzing, but after realigning the sound IF and detector transformer, the sound comes in good.

The sound IF was so far out of alignment (it was turned all the way one way) that I think someone got in there and messed with it, not knowing what they were doing. I think they probably did the same with every other adjustment, this is why I'm so certain my problem is alignment. Remember this was the set in which someone had also installed the wrong yoke and fly from another set.

I put some pics over on the arf a while ago, both with the 8XP4 test crt, and the set's own 16GP4. Retrace lines are a problem, but otherwise the picture's fine as long as there's no sound in the signal it's receiving. Completely 100% recapped all paper caps and electrolytics. I understand there's some micas in the horiz oscillator which also tend to go bad, but horiz sync is good, so they must be ok for now.

Adam · #9 12-27-2009, 05:36 PM

Now I tried the sweep generator, (sweep generator only, no marker generator here). I didn't adjust anything, I just wanted to see what the final response curve looks like. Now before I go messing with the alignment to try to get this to look right, does this look bad because of something I'm doing, or could the alignment actually be this far off?

I followed what it says in the sams. I have the sweep generator connected to a coil of wire wrapped around a 6J6 (from which I removed pin1). Using 4.5v negative bias between R21 and R30. And the scope is hooked to the grid of the video output tube.

Don Lindsly · #10 12-27-2009, 09:30 PM

It looks like a trap is misadjusted. Set them first with an AM generator. The rest may fall in.

Vary the bias somewhat to see what it does to the curve. If it is erratic, you may have a bad IF tube. Try the last IF and mixer first.

Don

Adam · #11 01-14-2010, 12:53 AM

I adjusted those traps, just setting them with the signal generator for the least deflection on the vtvm. And it did turn out the 3rd IF tube was very weak. Between those 2 things, I had it working much better. But then I messed with the rest of the alignment and made it worse.

So I worked to get the marker insertion unit working, and just now put it all together. I recapped the marker-adder and had to make several cables for it, but now it's working. At first it wasn't, but that was just one of the sweep attenuation switches not working because it was dirty.

The marker appeared on the trace on the scope, but it also seemed to modulate the entire thing. I put a .0047 cap across the scope vertical input, and it mostly eliminated that problem. Also the direction is reversed left to right with the lower frequency on the right and higher on the left, but I don't think that should really make any difference.

I'm not going to fuss with the actual alignment now, I'm just happy the whole set up is working. The pic below shows the 3-part RCA alignment set up, all stacked on top of each other, hooked up and working, with the tv chassis is hooked up to that b/w test jig. The sweep gen is on bottom, 2nd from the top is the "television calibrator" (basically a signal gen that goes up to 240MC) which generates the signal for the marker, which is then connected to the marker-adder (the unit on top of the stack) which adds the marker in after the sweep signal has been already demodulated by the tv, the vertical input of the scope then connects to the marker-adder.

Adam · #12 01-16-2010, 07:22 PM

When adjusting the 21MC trap, where the sound comes off, it didn't seem right that I had to have it turned all the way one way. I just noticed that the leads to the cap siting across it were shorting a few of the turns. I pulled the cap away and it made a big difference. I wouldn't be surprised if this wasn't the original source of my troubles with this set.

bandersen · #13 01-16-2010, 08:20 PM

Ugh! Nice catch

Adam · #14 01-17-2010, 01:02 AM

Made some major progress tonight. First, I got the alignment looking pretty good, so I decided to try it out. I set the tv to ch3 hooked it to a pair of rabbit ears, and fired up one of my B-T modulators transmitting on ch3. ... But the picture was worse!

Before, I could only get decent video with a modulator hooked directly into the set, with the output cranked. But I had put that down to the alignment, and that weak 3rd IF tube I found. And even so it still had poor contrast. ... Now, the video was not only poor contrast, but negative, white was black, black was white...

After a few hours of searching I found the problem, when I recapped the set, I hooked the .1mfd cap coupling the two triodes of the 12AU7 video amp, one side to the resistor after the cathode of the 1st half of the tube, rather than coil after the plate. Fixed that and now it works good.

I still want to mess with the alignment a little more. And I need to solder back in all the resistors I pulled up to test when I was looking for my video trouble.

Probably all that was wrong with this was the weak 3rd IF tube, the cap shorting that coil at the 21MC trap where the sound comes off, and that other cap I soldered in the wrong place. I probably really didn't need to do the complete alignment, but I'm happy I did, because I've wanted to learn how to do it for years, and I think the overall performance of the set is much improved over what it would have been had I didn't. I can go all the way from one end of the fine tuning range to the other and still get picture and sound and not loose sync, I've never had a round-tube era b/w set performing this well.

Adam · #15 01-17-2010, 02:41 AM

I touched up the alignment some more, then went back and redid the sound IF after I was done with the picture. Here's a pic of the curve I ended up with, the marker is sitting on 24.75MC. If I do this again, I'm making another cable so I can hook another signal gen up to the marker generator and get a marker at both ends of the top of the curve at once, it would have made it easier to have at least those two there at once.