The seleniums have long since been replaced by a pair of obligatory RCA 'tophat' diodes, sorry if that wasn't clear. I'm trying to correct B+ as a result, since it's now 60 volts higher than it should be. I've understand dropping resistors in the 150-200 ohm range should do the trick, I'll find exactly what value tomorrow or the next day.

OK here is what to do.

First, measure the current on the B+ line you want to place the dropping resistor into.

Now using Ohm's law solve for R. R=E/I ..... Plug in the current (I) in AMPS and the voltage you want to drop (E) in volts (60) and the solve for R (the resistance needed).

So lets assume 500ma is the measured current, the equation would look like this:

R=60volts /.5 Amps so R=120 ohms

Then to figure out how many watts the resistor needs to be use P=IE Where P the power in watts = the current (I) in AMPS times the voltage drop across the resistor E (which in this case is 60 volts)

Lets assume the following for the Power equation

P (watts) = IE so P= .5 Amps * 60 volts Therefore P=30 watts

No guesswork needed if you know the current flowing and the voltage drop needed.

The value of the resistance will not likely be a standard value, so get one of those tubular ceramic types with the adjustable slider band so you can adjust to the needed value.

Good Luck!

It is a great idea to use one of these! The calculation will get you very close, but there is a "second order" effect... As you drop the voltage applied to the circuit, the current drawn by the circuit will drop as well, and perhaps not in a linear fashion. Likely slightly more than the calculated resistance will be required to produce the desired voltage drop. Always nice to be able to make a slight adjustment! :yes:
jr

Exactly what I did, final value ended up being 75 ohms. My brother ended up having a 30-watt Ohmite resistor, I mounted it on a piece of angle aluminum and fixed that onto the removable plate that bolts to the HV cage. B+ is now a perfect 385, while the other line is slightly high at 292 ish. I think that will be just fine.

Important update: I have something on screen! :banana::banana::banana:

I ended up having to slightly rewire the power supply because of the B+ resistor I installed. At first I had some lines crossed, and that was causing a strange hump (like the negative going half of a sine wave) to appear in the vertical scanning waveform. It also screwed with the sync circuits, causing a no lock situation for both vert and horizontal. After fixing the B+ supply, the voltages fell perfectly in line and the scanning waveforms looked perfect as well as having perfect sync. I had been injecting a signal into the video amp tube, because I wasn't sure of the condition of the tuner. Now that I have things in order though, I hooked the tuner back up and it works just fine. :thmbsp:

Color is even trying to work, but it's not quite there. I think I'll probably end up having to do a full on chroma alignment, even though it pains me to think about it. Last time (on the CTC-7), it took like a weeks worth of fiddling to get things to fall into place. :sigh:

Here's a pic of what I have thus far:

As you can see on the above screenshot, covergence is still horrible and there are bad purity issues. Right now the raster buttons on the NTSC gen have little effect, so I'm thinking it's now time to delve into the demods and figure out why I can't get the chroma part of the chassis to do anything. Once I get that sorted, I should be able do the screen tweaks necessary to get a nice picture up on the tube.

I hope you don't really mean a full chroma bandpass align first. First thing is to make sure the oscillator locks and then that the tint control is centered. And really, before that, why not work on getting the purity at least approximately right, so you can see if the tint looks OK.

Well, first I have to see if I can get the driver tubes to do the right thing. Otherwise anything in the chroma circuit is pretty useless. I can see right now that the local oscilator does in fact lock, because there are bars that will float by vertically then lock in. It's only visible as a slight change in brightness right now, but it's there. I scoped the burst amp tube a bit ago, and it looks like the burst is gated correctly and getting through to the rest of that section, so at least I have that much going for me. I think for now the right thing to do will be to see if I can somehow get the purity magnets mounted (something like what you had to do to your 5), and sort that out.

Before any of that though, while I was scoping the burst gate (amp, whatever) I smelled ozone coming from the HV cage and heard leakage. Pretty sure I'll have to pause and replace the filament windings for the rectifier tubes before going any farther, so I'm off to scrounge some 40 kv wiring.

Oh, I almost forgot: I was perusing Ebay the other day, and found myself an RCA WP-25A Isotap isolation transformer for the pauperly sum of $25. Should make a nice addition to my vintage arsenal of electronic tools. :p

Today, I was working on the set and the smell of ozone was in the air. I suspected the old HV wiring in the cage was to blame, so I set about replacing it. I have a slew of newer chassis in the garage thanks to Doug, so I grabbed a spare Sylvania chassis and robbed the wiring from it. The old CTC-4 stuff was cracked in a few places, so I have no doubt there was leakage occurring. It was only single jacket stuff anyway, the new stuff is more modern double jacket.

First I replced the filament winding for the 3A3 rectifier, holding it in place with shrink tubing around the flyback core.

Then I tried to replace the wire on the focus rectifier, but it was no use due to the molded cap. I didn't have a spare small size top cap, so I had to carefully remove the one on the tube and solder a bigger one on to it. This involves carefully grabbing the cap with pliers and slightly twisting it, so the old glue will break free of the glass. Then it's simple to desolder the cap, and replace it. I took the replacement one from a dead HO tube, and used epoxy to glue the metal cap onto the top. Then I used a normal size connector, some more replacement wire, and sealed the connection on the flyback with non-acetate RTV. I doubt there will be any leakage from there now. :thmbsp:

Also, for some reason there was a 22K resistor in series with the anode cap lead. I couldn't find it anywhere in the schematic, so it was removed. There seems to be more range in the focus control now, so that's good.

Back to the rectifier. Having already replaced the filament wiring, I now soldered that to the socket. That brought me to the wiring under the socket, which connects to the HV capacitor and HV tower on the side of the cage.

I never really liked the way the HV capacitor was connected under the rectifier cup, with an 'X' shaped solder lug. It screwed into the capacitor, then the rectifier cup and HV tower connection soldered to that. This made wire breakage an issue, since to remove the cage means leaving the tower flapping in the breeze.

So I made a short wire with round terminals on each end: one screws into the cap, the other end goes to the top of the rectifier cup.

This does 3 things for me:

1. I can pull the rectifier cup and the cap doesn't fall out now, because there's still a screw and a lug holding it in.

2. It also allows me to remove only the cap if I choose, since I can put a phillips screwdriver down the center of the tube socket (no need to pull the cup if I just want the cap out).

3. the HV wiring is now modular. The HV tower can be disconnected from the rectifier cup, so the tower and shunt reg cap all come off in one piece. Very neat now, and I no longer have to pull the cover of the cage to get the cage off the chassis. I simply remove 1 screw from the rectifier cup, and the whole cage comes out in one piece.

The pics below show what it looks like now. :smoke:

And now, for the grand finale!


After a few tweaks to the demod driver transformer, we now have color bars!

:banana: :banana: :banana:


Purity and convergence are still a mess, but this proves that 99% of the parts in the chassis are doing what they are supposed to do. That makes me very happy indeed, since this thing was a basket case of prior hacks when I first picked it up. Twice rebuilt picture tube, melted insulation, frazzled video peaking coil, bad solder joints, and more incorrect connections than I can count on both hands...

Along the way, I also found that whoever replaced the flyback had mistakenly swapped terminals U2 and U3, which supply pulses to the blanker and burst keyer tubes. Not sure how much difference it makes since the voltage difference in the actual pulses is small (50 volts), but I fixed it anyway for the sake of correctness.

Congratulations - but your dancing bananas are purer than your color bars :D

That set is looking nice already. Keep up the good work.

COOOOOOOL ... just plain COOOOOL

Did more work the other day, and discovered that I would never get correct purity without the correction magnets- this CRT has a large area of impurity in the lower left hand side. So I installed the magnet assembly around the CRT, and tweaked it best as I could. Result is below, how's it look now Wayne? :D

hey hey - much nicer :thmbsp: :tresbon:

Nice :thmbsp:

That looks really nice! Mine has a very small purity problem in the lower right corner, and I think it might be due to the tube needing to be degaussed, but I'll try the magnet again. The rest of the screen is just right.
BTW, I notice that your 4 also doesn't fill the screen all the time at the left side. Interesting; mine does the same thing. If I increase the line volts to 120 I can get a full pic. These things have notoriously poor voltage regulation, so maybe that's one of the problems. Don't want to screw around with the width circuit again yet.
Kevin :thmbsp:

I tried degaussing this one too, but the spot persists. It's pretty close to optimal, but there's still a tiny little area I can see where it's not right. It's a shame, because the tube checks as new on the tester. None of my other sets even needed the purity magnets, the screens are just perfect.


I haven't yet messed with the width controls on this set, because the replacement centering pot's shaft is too short for the knob to fit on it. I think once I graft an extension on it and adjust horizontal width, the screen will look normal.

Can you post a pic of the total CRT back magnetics? Does this set have the little hairpin-shaped purity poles on a tube mounting ring (around the CRT bell) like the CTC-7 mount I put in my -5 to accomodate the 21FJP22? Those hairpins do make a difference in uniformity of the purity.

If this chassis has the multiple magnets around the edge of the face, I'd suggest removing them when using a glass tube. They were necessary for the metal-bell tube, which strongly distorts the fields very near the edge, but their effect is probably too strong right at the edge of the glass tube and falls off too rapidly towards the center.

No, it has a band with round magnets on it. I need to do the same thing you did on your 5, but I don't have a spare set of hardware to modify. My main issue is what to do with the yoke; it doesn't mount to the CRT neck, it's held by the large metal piece which also supports the CRT. Perhaps there's a way to use a later yoke with the pull up ring?

Looks like you have the edge magnets screwed out towards minimum strength - I'd guess that's the best position. If the ones on the bottom aren't screwed out all the way, you might try that. Also, if you have a small refrigerator magnet, you could try moving it around the bell about halfway back to see what effect you get.

I'd try getting the purity with added magnets before changing the hardware. I had no choice on the -5 when I went to the glass tube.

Yes, most of them are at min strength. The only ones I had to actually use were the ones at the bottom left side of the tube, and you're right, thye are a strong effect at first but it quickly diminishes at the center. I'll try an additional magnet farther back, sounds like a good idea.

I noticed that the crosshatch pattern looks funky, anyone ever see something like this? It looks mostly fine, until the solid horizontal line passes through the vertical one right in the center. It's like the horizontal line causes some ringing in the video amp or something, see the squiggly vertical line? It also looks funny on the left side, something that was pointed out by a member on ARF. At first I didn't think anything of it, but there's clearly an issue there. See how the horizontal lines continue off screen, while the vertical line of brightness that stops near the edge?

I checked my other sets, and they don't do this. Think maybe it's because of all the inductors in this chassis? It does have 10 times the number of peaking coils than any other chassis I've worked on, but I'm inclined to believe it should still be able to display a simple cross without an issue. Thoughts?

Second shot is just more brightness than the first.

looks like sync separator problem - white video causing the sync to be clipped at a different level. I also notice it occurs at the top, where the horizontal sync has been disturbed by vertical sync Do you have a multi-square crosshatch? Does the wiggle follow every horizontal white line?

Also might try turning the noise threshold control to see if it affects this.

I was thinking sync as well, but it's so darn stable! I can twist the horizontal control multiple times, and it stays locked. Vertical is pretty solid too, is it possible to have stable sync while still having an issue? Yes, it happens with the multiple chrosshatch too- at the intersection of every horizontal line, the vertical gets a little squiggle to it. Noise inverter and AGC have no effect on it.

Well, now I'm just fishing, but have you checked component values in the horizontal oscillator/control section? Even if it's getting an input jolt it shouldn't get, I think it maybe should respond with a more damped response instead of a decaying oscillation.
The following three components are the main control loop filter:
C160 .01
R165 3900
C159 0.47

+ other R's and C's in the vicinity

All the caps and resistors in the horizontal section are either new or within tolerence. I thought I was having a problem with the originals before, but it ended up being a power supply wiring glitch that was my fault. The power supply is fine now, and I strongly doubt issues with the oscilator.

Thanks, Wayne! :D


In the end, you were right. When I initially set this thing up, it still had a miswired power supply with 60hz noise. That means I tuned the horizontal sine coil with that same noise in it, but I failed to recheck it after I corrected the problem. Looked at it with the scope the other day, and sure enough the first hump of the waveform was was lower than the second one! I watched the screen as I tweaked for equal humps, and sure enough that coil being detuned will cause the ringing I was seeing. Now I have nice straight lines on the screen, just like I should. :banana:

I wasn't thinking of the sine coil, but it makes sense because it could affect the pulse shape going to the phase detector. Glad you found it!

No matter, you got me looking into the horizontal section and that's what sparked my pot-frazzled memory. :smoke:


OK, so at this point I did a very rough setup with the bar gen and reconnected the tuner. Still have some issues with a dirty AGC and color killer pot, those will be next on the clean/deoxit schedule. Here's the result, as seen via the Crapcast DVR! :thmbsp:

Getting very close to a good picture now, all I have to do is another round of purity/convergece,
and nail the color alignment. What was that about keeping me off the streets for a while? :D

Did work on red purity, and was able to just about cure that patch on the bottom of the screen and left hand side. Looks pretty good now, aside from a few little issues with red convergence in the bottom right corner. Can't really see it from normal viewing distance. I think I'm gonna call this a winnah for now, I'd like to enjoy it for a while before I send it off for refinishing. that will be the next problem, since all the people who work on wood around here are booked till the return of Christ. Any leads on someone who's free to do that kind of work?

I know a great refinisher here, but you probably don't want to ship the cabinet to Seattle.

Looks like you're making real progress. I'm glad you mentioned the horizontal squiggle. I have seen that before (don't recall exactly when). If I see it another time, I'll know what to look for.

Phil Nelson

No, I'm definitely not up for shipping it across the country. I'll just have to keep bothering the refinishers around here till they help me I guess, I just can't believe more people aren't getting into woodworking. With the economy in the tank, you would think people would flock to a trade that's always telling me they have no spare time to help...

Maybe they just want nothing to do with an old TV cabinet.

Thanks for the nice Sams CTC-4 Photofacts, Brian! Now I can align the matrix correctly.

OK, overdue update!

Long story short I was able to get acceptable matrix alignment after a long time messing with it, but the 21FJP22 CRT I borrowed from Mark has some purity issues that the CTC-4 magnets cannot correct. What it needs is more correction closer to the center of the screen, and the -4 edge purity ones run out of steam after a couple inches or so. I think I could get it near perfect if I had a spare CTC-9 purity ring assembly, but I don't have one. I'll either save it for another set, or give it back to Mark so he can put it into one of his. It has perfect emission.


Which leads me to the next big thing- Tom Schulz over on ARF was very generous indeed by GIVING me a 21AXP22A for free! Neither of us was sure if it even worked, but I just put it in and it has a raster!!! :banana: :banana: :banana:


Much more to come in a short while, the tube obviously needs to be set up. But from what I can tell right now all the guns respond to the screen controls, and I can see a plain image on the face. Here's hoping for the best!

It's confirmed, the tube is good! :thmbsp:


Now off to do a full setup...