CTC-5 Westcott restoration

[old_coot88]

In your screen shot it looks like the chroma level, color sync etc. are good. So turn the color control completely all the way down. Forget about color for now. It's a completely separate system from the luma (B&W video) chain. With the color off, the set should show a normal B&W picture.
The luma chain is what you need to work on.
-----
On a related note, remember that in a tube type color set, luma goes into the CRT via the cathodes; color goes into the CRT via the (G1) grids.

[Bill R]

Bad Delay line or last video amplifier. Check the delay line and the connections to it.

[TUD1]

Much improved! Still looks a bit washed out, though. On the video I mentioned earlier, the Westcott had a sharp, rich picture.

[SwizzyMan]

I did some reading up on the A version of the 21axp22. The red dag coating was used to prevent internal arcing in the neck of the tube. Does this imply that the original 21ax had arcing issues inside the neck? We're the phosphors on the A version improved over the original?

[miniman82]

There are at least 3 flavors of 21AXP22 that I'm aware of:

The earliest ones had the same phosphors as a 15GP22 giving a greenish look to the screen and had normal grey dag on the inside, the chassis they were used with always had series anode resistance to protect the flyback in case of an arc in the CRT. Part number would be 21AXP22.

Next is the same tube, just with improved brightness from different phosphors. This one was used in most of the CTC-4's you see out there unless a replacement was installed, and it's easy to tell because the screen appears white instead of greenish. Part number is still 21AXP22, still all grey dag.

Last version to come out before the glass tubes was the 21AXP22A. This is the one with a white screen and red resistive dag on the inside, which eliminated the need for series anode resistance for arc protection from the previous model. All CTC-5's used this tube and it's compatible with earlier chassis.

The same is NOT true of putting a 21AXP22 (non-A) into a set having a CTC-5 chassis, which has no built in series anode resistance. While it's true it will 'work', the caution there is that without any series anode resistance you run the risk of shorting all HV anode current to ground in the event of a CRT failure. The whole point of series anode resistance is the protect the chassis, without it you blow up more parts when the CRT goes. So if you have a CTC-5 and your CRT has all grey dag, either install some resistance in the anode lead or prepare to replace the flyback if the tube dies.

The red dag doesn't prevent arcing, it merely saves other parts from death should an arc occur.

[SwizzyMan]

Checked the delay line. There were two leads coming out of one end and just one lead coming out of the other end. One of the two leads read .1 ohms and the other lead read 830 ohms. The side reading 830 ohms sounds like it could be causing the complete absence of luma. What do you folks think?

[old_tv_nut]

Originally Posted by SwizzyMan

Checked the delay line. There were two leads coming out of one end and just one lead coming out of the other end. One of the two leads read .1 ohms and the other lead read 830 ohms. The side reading 830 ohms sounds like it could be causing the complete absence of luma. What do you folks think?

Your latest picture does not show complete absence of luma, although it does look like the brightness control is way too high, washing out the blacks. Do you have the service manual that gives the CRT bias setup procedure?

Regarding your delay line resistance readings, are you measuring in-circuit or out? And exactly where are you connecting the ohmmeter?

[SwizzyMan]

Originally Posted by miniman82

There are at least 3 flavors of 21AXP22 that I'm aware of:

The earliest ones had the same phosphors as a 15GP22 giving a greenish look to the screen and had normal grey dag on the inside, the chassis they were used with always had series anode resistance to protect the flyback in case of an arc in the CRT. Part number would be 21AXP22.

Next is the same tube, just with improved brightness from different phosphors. This one was used in most of the CTC-4's you see out there unless a replacement was installed, and it's easy to tell because the screen appears white instead of greenish. Part number is still 21AXP22, still all grey dag.

Last version to come out before the glass tubes was the 21AXP22A. This is the one with a white screen and red resistive dag on the inside, which eliminated the need for series anode resistance for arc protection from the previous model. All CTC-5's used this tube and it's compatible with earlier chassis.

The same is NOT true of putting a 21AXP22 (non-A) into a set having a CTC-5 chassis, which has no built in series anode resistance. While it's true it will 'work', the caution there is that without any series anode resistance you run the risk of shorting all HV anode current to ground in the event of a CRT failure. The whole point of series anode resistance is the protect the chassis, without it you blow up more parts when the CRT goes. So if you have a CTC-5 and your CRT has all grey dag, either install some resistance in the anode lead or prepare to replace the flyback if the tube dies.

The red dag doesn't prevent arcing, it merely saves other parts from death should an arc occur.

My bad, I interpreted this post wrong. I thought the greenish tint was a picture related effect. Not just the color of the phosphors. Also I know know that the A version of the 21ax didn't even have that same phosphor.

[SwizzyMan]

I am currently solving a horizontal issue with this set. I have since fixed this but it seems the tuner and IF circuits have gone out of whack. Ive tried all adjustments and tubes. What I would like to do since this TV will soon be in a cabin in Minnesota where over the air and cable is hard to find is to see if it is simple to inject a composite signal into the video and sound amp to bypass the tuner and IF. Is this possible by just connecting a direct video source or will I have to build a preamp for this set too?

[old_tv_nut]

See the setup procedure attached.

Regarding the resistance readings of the delay line in circuit, it is very complicated to tell what they should be because you are measuring everything connected to it. The only way to be sure is to have readings from a good set to compare to.

The alternative is to disconnect the line and see what readings you get of the line by itself. There should be conduction from the input to the output and no conduction from either the input or output to ground.

I'm not sure what the normal resistance is between input and output, but I suspect it will be low, as theoretically the line is supposed to work by a combination of distributed inductance (the coil) and distributed capacitance (the coil is wound on a thin insulator over a ground foil).

[jr_tech]

Possibly a reasonable test would be to simply by-pass the delay line and observe if contrast is greatly improved? :

Of course the picture would be a little strange looking, as the luminance signal would be slightly ahead of the color signal, but it should give you an indication of the operation of the delay line.

jr

[SwizzyMan]

How would I replace the delay line if it might be bad? The setup procedures did not seem to do anything. Maybe something in the contrast circuit could be bad?

[SwizzyMan]

Starting to think that the delay line is not the issue here. I can get an OK crisp picture but only with the contrast, color,and brightness turned down pretty far. Only watchable in a dark room. I checked two of the pins on the 12BY7A video output tube (plate and screen grid) and found that both voltages on the pins are off. This must be an issue with a resistor in the 12BY7A portion of the board. I must note I wired in parallel two 1 uf film caps to create a 2uf cap to replace the electrolytic that was there. The schematic calls for a 2 uf cap but the one I removed was an 8 uf. I never found any production changes stating that a 8 uf should be used instead of a 2 uf. Maybe I should try an 8 uf?

[old_tv_nut]

If it's any consolation, I have never been satisfied with the luma drive level on my CTC-5. It seems the chroma sections have much more capability. It's on my "some day" list to revisit this issue, but now that it's been brought up, maybe someone else here can comment.

One thought: check the AGC and make sure you have the proper video level at the video detector. Also try substituting video output tubes. In the Magnavox set I had, I found that the output tubes varied quite a bit and you could get more gain out of some than others. I think the luma channel is really pushing to get enough gain out of the final tube.

[SwizzyMan]

perhaps a contrast mod would be wise?