Any idea for a substitute crt for a 21zp4a ?

21YP4 but it will require modification.

21ZP4 is magnetic focus. 21YP4 is electrostatic.

So you would need to remove the magnetic focus coil from the neck. It's probably part of the power supply though so you maybe need to leave it electrically connected or replace with a filter choke

The focus is electrostatic , I assume it would need a focus circuit.

Nope. Just strap it to G1 or G2. They used a little shorting strip of metal that would slip over the CRT pins

Nope. Just strap it to G1 or G2. They used a little shorting strip of metal that would slip over the CRT pins

Your right I have a small b&w set with that metal strip for focus on it. Does it matter which pin g1-g2 and the 21yp4 don’t require an ion trap and is it aluminized

Try it on different pins and see what looks best. Some sets ran focus to a connector that let you choose between those taps and B+ boost.

Well come to find out this set does infact have a 22yp4a with the 6th wire for focus so if this originally had a 21zyp4 what does this focus magnet look like where is it next to the yoke maybe it was not removed I don’t know since focus could be better. How do you get the year of a ge crt 6113

Assuming it is electromagnetic, like this.
https://live.staticflickr.com/5581/14859258534_9a623e01c2_c.jpg (https://flic.kr/p/oD4zSE)

If it's a permanent magnet type. Like this.
https://live.staticflickr.com/587/21338222986_06221e6a00_c.jpg (https://flic.kr/p/yvzYhj)

This yoke is much smaller then these pics so it looks like there is no magnet it’s just the deflection coils and the front has the slide magnets that’s it. Is there a formula to figure out the year this tube is ge 6113

Well if I had to guess - 13th week, 1961.

There is a tuning capacitor on the chassis that says horizontal frequency is this used to set high voltage if it’s not right? One last question the power transformer has the 5u4 tube for b+ is the heater voltage separate from the rest of the tube string wondering if I ever tried using the plug in rectifier

I have no idea. What make and model is this TV?
A 5U4 is directly heated so you can't power the filament from a series string.

It’s a 1954 cbs Columbia 21 inch

I don't think I have ever seen a set where the 5U4 doesn't have its own heater winding... Only time there's another tube on the 5U4 winding it's a second 5U4 put in parallel for increased B+ current capacity...the 5U4 heater is always the B+ source so if anything else shared it the heater cathode voltage would violate tube specs.

Any knowledge on who built the chassis for cbs Columbia?

This Columbia is getting weird now there is no focus voltage on pin 6 but yet the picture is not that bad as far as focus and there is no jumper on the crt and no magnet on the neck how can this be.the schematic don’t show where focus voltage comes from just says if using electrostatic tube then use pin 6. This chassis has a focus pot and an electrostatic tube but schematic I have shows no focus control because it shows the magnetic tube.

Well looks like one side of the focus pot is open and it’s a 1 meg but I have a 2 meg I’ll try should work will just be more to one side.

Got the focus voltage back only now the hv is to low should be between 15-16kv I only have 10.2kv how is the hv adjusted in these old 21 inch b&w sets. And what causes a bright dot in the center of the screen when turned off.

A bright center spot after turn off is normal for some sets. It depends on the relative rate of decay of the high voltage and the video output voltage. As long as the phosphor is not getting a dark spot burned in it, it's OK.

A bright center spot after turn off is normal for some sets. It depends on the relative rate of decay of the high voltage and the video output voltage. As long as the phosphor is not getting a dark spot burned in it, it's OK.

Is there a way to adjust the hv? The other post I said hv was 10.2 kv not correct , it is 12kv for a 21 inch tube I would think it should be up around 14-16 kv datasheet says typical.

The focus voltage is not where it should be it’s at 286v while sams shows +305 v

Adjustingthe horizontal freq. & drive, use fresh tubes, recap etc. Make sure B+ is where it should be.

The focus voltage is probably derived from the boost voltage which comes from the flyback damper circuit. So, if you have low HV, the boost * focus voltage are probably low.

You really need a schematic. What model # is it?

Adjustingthe horizontal freq. & drive, use fresh tubes, recap etc. Make sure B+ is where it should be.

The focus voltage is probably derived from the boost voltage which comes from the flyback damper circuit. So, if you have low HV, the boost * focus voltage are probably low.

You really need a schematic. What model # is it?

I have a schematic it’s a 22c38 cbs Columbia. It’s been recapped tubes all good and tried moving the horizontal frequency drive won’t go any higher then 12 kv turn it any more and I get the line down the center. Focus voltage is low as well.

Never know what was done to a tv over the years maybe the afc was messed with along with the horizontal drive.

22C38 has many variations and covered in Riders 14, 14 and 15.

Do you know if you have

Chassis
750-3
750-43
750-81
751-3
752-1
752-2
821-3
821-10
822-1
822-2

22C38 has many variations and covered in Riders 14, 14 and 15.

Do you know if you have

Chassis
750-3
750-43
750-81
751-3
752-1
752-2
821-3
821-10
822-1
822-2
Oh where can I find this number I don’t remember seeing s number like these

This tv has no horizontal hold and there are no controls in the front only channel and turn on volume knob and has the electrostatic tube and it’s a stand up console type with a big speaker in the front bottom maybe this helps.

Would it make much difference to replace a 60 ohm 10 watt resistor with a 50 ohm 10 watt resistor in the b+ Because I have a 68 ohm in there now I don’t know what maybe better higher or lower

Probably has a synchroguide horizontal circuit. Is there a connector on the rear chassis that says "color wheel adapter"? Gosh, I wish I still had that set!

Any knowledge on who built the chassis for cbs Columbia?

They built it themselves. In the early 50s to compete in the color wars CBS Columbia bought out a TV maker IIRC Air King and changed that makers name to CBS. The FCC wouldn't hear color TV standards proposals from broadcasters, you had to be or own a TV set manufacturer to submit a proposal.
A few years after the color wars were lost by CBS they sold or divested their TV manufacturing division and the brand ceased to be.

They continued as CBS Laboratories. They made the Audimax and Volumax which were the standard for radio stations for many years.
Also they made the Vidifont, which was an electronic typewriter for TV stations. It loaded fonts from 8 inch floppies. (Remember those?) It was a wired logic design. It was superseded by the Chyron which could do graphics. It had a microprocessor. It also used 8 inch floppies.

Does this match your set?

Riders vol 13, chassis
https://live.staticflickr.com/65535/54421310252_7cda8a119c_c.jpg (https://flic.kr/p/2qV2rwC)

First time I have ever seen a focus control on an electrostatic focus set. Usually, it's a jumper with 2 or 3 options.
I've been curious if it gives a smooth focus change. If so, why didn't more sets use a variable control?
https://live.staticflickr.com/65535/54422161426_50e669d36e_b.jpg (https://flic.kr/p/2qV6Ny3)

Lots to check for low HV.

6BQ6 HOT
1AX2 HV rectifier
6W4 damper
1M resistor in series with HV lead
0.51 ohm current limiting HV rectifier resistor
500pF, 20kV HV filter cap
Horizontal grid driver amplitude

Does this match your set?

Riders vol 13, chassis
https://live.staticflickr.com/65535/54421310252_7cda8a119c_c.jpg (https://flic.kr/p/2qV2rwC)

First time I have ever seen a focus control on an electrostatic focus set. Usually, it's a jumper with 2 or 3 options.
I've been curious if it gives a smooth focus change. If so, why didn't more sets use a variable control?
https://live.staticflickr.com/65535/54422161426_50e669d36e_b.jpg (https://flic.kr/p/2qV6Ny3) we’ll the tube line up looks the same but it shows the magnetic focus tube which would be different if it’s got the 21yp4 then it’s probably the right one.

All tubes are 100% anode wire resistor good limiting resistor measures 1.7ohms and the 1x2 heater does light up,, correction I measured with the tube in so I probably measured the heater filament but it does light ok. Limiting resistor is 0.7ohms

The schematic shows both. The dotted line is the for the electrostatic focus CRT.
Anode wire resistor should be 1M, not 1.7 ohms.

Filament limit resistor should be 0.51 ohms. 0.7 is close but it will run the rectifier tube a little lean and could possibly reduce the HV output.

The schematic shows both. The dotted line is the for the electrostatic focus CRT.
Anode wire resistor should be 1M, not 1.7 ohms.

Filament limit resistor should be 0.51 ohms. 0.7 is close but it will run the rectifier tube a little lean and could possibly reduce the HV output.

The anode resistor is .93 just shy of 1 meg yup I see it I missed that in the schematic for both. The 60 ohm resistor for the b+ I have a 68 ohm in there that measures 69 ohms could I put a 50 ohm in there instead ?

Does this match your set?


First time I have ever seen a focus control on an electrostatic focus set. Usually, it's a jumper with 2 or 3 options.
I've been curious if it gives a smooth focus change. If so, why didn't more sets use a variable control?


Some 60s Zeniths had it. It didn't have a very sharp peak IIRC so it was probably seen as about as good to jumper (only cheaper) by most makers

Unless I had the correct sams I can’t go on some voltages, I have b+ 360v focus 351v and boost 575v seems high since the sams I have says 490v boost and b+ 305v and focus should be 300+ I’m not sure where the hv should be it’s at 13 kv , bright down close to 14kv

What is the difference between the old wax yellow caps and the black bumble bee caps. What can go in place of the bumblebee cap.

I'd use orange drops. If you can find them. Don't be vague. ask for Sprague.
If your voltages are within 15% they are probably OK.

What is the difference between the old wax yellow caps and the black bumble bee caps. What can go in place of the bumblebee cap.

The only difference between a bumblebee (paper dielectric like most plastic body tubular caps of the era) and a wax paper cap (also paper dielectric) is the plastic housing designed to keep moisture out. Both suck equally bad. Replace with any decent film caps. Orange drops are good assuming they aren't too old (I've seen nos 60s specimens that were going bad), new production I favor the maroon ceramic coated Panasonic film caps mouser and digikey sell. Good quality and reasonable price.
The yellow caps some of the radio vendors sell are good to despite some disliking their aesthetic. Just don't melt the body with your soldering iron. They are good for restuffing which is my main use for them.

The only difference between a bumblebee (paper dielectric like most plastic body tubular caps of the era) and a wax paper cap (also paper dielectric) is the plastic housing designed to keep moisture out. Both suck equally bad. Replace with any decent film caps. Orange drops are good assuming they aren't too old (I've seen nos 60s specimens that were going bad), new production I favor the maroon ceramic coated Panasonic film caps mouser and digikey sell. Good quality and reasonable price.
The yellow caps some of the radio vendors sell are good to despite some disliking their aesthetic. Just don't melt the body with your soldering iron. They are good for restuffing which is my main use for them.

So would that mean a ceramic disc is out of the question ?

So would that mean a ceramic disc is out of the question ?

Not recommended, as they tend to drift, unless they are a very stable NPO type.
https://www.allaboutcircuits.com/technical-articles/x7r-x5r-c0g...-a-concise-guide-to-ceramic-capacitor-types/

So would that mean a ceramic disc is out of the question ?

Generally if an original cap in a TV is paper it's a bad idea to replace it with ceramic...you can get away with it in audio circuits and input power line noise bypass caps, but I wouldn't use them elsewhere unless the original cap the manufacturer used was ceramic.
Replace paper caps in TVs with film caps if a sufficiently close modern film caps value exists.
You can get some spooky issues and strange drift from ceramics doing a film caps job.

Do these width coils that are in the old b&w TV sets work , how far do you have to turn them in or out to get a response on the screen.

Yes, for fine adjustment. Maybe 1/2" - 1" from one extreme to the other.

Generally if an original cap in a TV is paper it's a bad idea to replace it with ceramic...you can get away with it in audio circuits and input power line noise bypass caps, but I wouldn't use them elsewhere unless the original cap the manufacturer used was ceramic.
Replace paper caps in TVs with film caps if a sufficiently close modern film caps value exists.
You can get some spooky issues and strange drift from ceramics doing a film caps job.

What Tom said ^^ it's important. And in audio circuits, I know that many disc caps were used. But if I need to replace them due to damage etc., I use film in HiFi amplifiers because at high frequencies, the Piezo effect "may" affect the frequency response. Film caps are inexpensive.

In TV sweep circuits, it's probably important to go type for type. I don't try to second guess the engineers, even though they were often badgered by the bean counters

Is there a procedure when setting these b&w tvs up. What is first , the ring magnets on the tube neck and then the width and then other settings on the rear. The sams don’t specify anything.

Not really. They're designed to be plug-and-play when they left from the factory. BUT after repairs some adjustment may be needed to the circuits that were repaired.

The door knob capacitor do they lower in value with age.

No. Ceramic and very stable

Correct, don't expect them to test at EXACTLY 500pf , or whatever, if one does fail, it will be to short to ground, or break apart, which is very rare.

Correct, don't expect them to test at EXACTLY 500pf , or whatever, if one does fail, it will be to short to ground, or break apart, which is very rare.

Ok was just wondering because this 500pf tested at 400pf just still looking around why I cannot get the hv higher.

Did you check the items I listed earlier? Especially the grid drive voltage?
Is it running on frequency?
Do you have a stable image?
Swap damper and horizontal output tubes.

Did you check the items I listed earlier? Especially the grid drive voltage?
Is it running on frequency?
Do you have a stable image?
Swap damper and horizontal output tubes.

I tried another horizontal tube and the image is very good and stable I have no way to check frequency but if I turn the horizontal drive pot the hv will only go up alittle not enough and I get the drive line down the center of the screen and have to put it back down where it was. The grid drive voltage where do I get that from the horizontal output tube ? I’m going to swap the damper and try that. Not sure if this grid drive voltage is listed in this sams I have.I just took a look and it turns out that there is a 6ax4 damper in there but it supposed to have a 6w4 so I have a new one I’ll try.

If you have a stable image, the frequency is correct. I mean use a scope to see the drive AC waveform amplitude.

6AX4 should be fine. Very similar spec to 6W4.

While the 21yp4 is electrostatic the other 21zp4 is magnetic so is there another way to focus this 21zp4 without the focus magnet setup from the factory. The sams shows hv is 10.2kv for the 21zp4 but if anyone has a sams for the cbs Columbia with the 21yp4 electrostatic tube maybe the hv is the same or different I maybe chasing something for nothing if both tubes are listed at 10.2kv. I already tried setting the hv to 10.2kv but it’s clearly not enough because the screen pulls in typical not enough hv.

Timmy, what are you using for a signal source? If you don't have a B&K Analyst, you should have at least a Howdy Doody Test Generator.

Timmy, what are you using for a signal source? If you don't have a B&K Analyst, you should have at least a Howdy Doody Test Generator.

I have a bar generator and a good tv signal source but that’s not the issue the problem is this set I’m certain it is supposed to have more hv which I cannot get it plays great other then that.

OK. Try this. After the set runs for 5 minutes, turn it off. Then put two fingers on either side of the coil on the flyback and see if it's hot.
What type of bar generator do you have?

OK. Try this. After the set runs for 5 minutes, turn it off. Then put two fingers on either side of the coil on the flyback and see if it's hot.
What type of bar generator do you have?

Flyback does not get hot and I have an rca wb-64a

5pf and 10pf mica these are in the hv area so if i were to use ceramic then I assume it should be npo. These micas were not changed since I was not able to find this value with a voltage of 2500v. Ceramic seems like the best way to go. But the sams shows these caps as mmf so this could also mean ceramic I’m thinking. Besides npo what is z5f and z5u

If I go by the sams and set the hv to 10.2kv like it shows the screen pulls in on the left and right about a half inch on each side but I may not have enough to adjust the width to fill it in being the width control only goes alittle bit. And either way the focus should be better but it’s not and it’s said that these big electrostatic tubes have very little focus control. Sams says 305v for focus I go 305-344v and makes no difference. I should try it and rule out if the width will fill it in.

Setting the HV higher will likely cause the image to shrink. It's harder to deflect a more energetic electron.

Now the flyback also drives the horizontal yoke winding so it's not quite so simple. Generally, the more energy you dump into the flyback, the more HV and more deflection so they track.

Really it depends on the design and component matching. There's usually a sweet spot when you get the lowest cathode current, most HV and full width. That's why there are so many adjustments - hor. drive, width and linearity all need to be set properly to get optimal results. That's a bit of a black art.

Setting the HV higher will likely cause the image to shrink. It's harder to deflect a more energetic electron.

Now the flyback also drives the horizontal yoke winding so it's not quite so simple. Generally, the more energy you dump into the flyback, the more HV and more deflection so they track.

Really it depends on the design and component matching. There's usually a sweet spot when you get the lowest cathode current, most HV and full width. That's why there are so many adjustments - hor. drive, width and linearity all need to be set properly to get optimal results. That's a bit of a black art.
Well as of now I guess it’s safe to say I got the best sweet spot the screen is stable focus is acceptable and it looks good. I did set the hv to 10.2kv but the width couldn’t open it up was to much. I went over so many times with the both vertical adjustments afc to stabilize the horizontal hold and adjusted the rings on the neck I don’t think it can get any better since these sets will never be perfect. And when I lowered the hv it pulled in on the left and right but if I raised the hv to 13 kv a white line begins to show in the center of the screen 12 -6 position.

I think there's an old trick to increase width by putting a ceramic HV cap across the damper tube

I think there's an old trick to increase width by putting a ceramic HV cap across the damper tube

Hmm well I never heard of that but I think I got it as good as it will be so I think I’ll leave it alone and not add any problems 😂

GC made a wafer with built-in cap you could install between the damper tube and socket. I'll post a photo when I dig mine up.

GC made a wafer with built-in cap you could install between the damper tube and socket. I'll post a photo when I dig mine up.

That would be interesting to see. At this point I just wanted to try and make sure all was right so lowering the hv to 10.2 kv down from 12 kv would be the only reason to widen the screen so now it’s at 12 kv with full screen and width and height and linearity are good. How much would that cap for the damper expand the width ?

How would you adjust a 7810 positive regulator to output 5 volts with an input of 9 volts I know a resistor is used but which terminal and how to determine the right resistor.

A 7812 will not regulate with an input of 9V. If you want 5v output I would use a 7805 regulator. They also make 7806 and 7808 and I think 7809 regulators along with 7815 and 7824 regulators. You can use an LM317 as a variable voltage regulator. You should be able to find some circuits on this here web.

+1 .
you can with a couple of resistors make a 78xx series regulator output a higher voltage than it's design voltage (the last 2 digits of it's part number) but you can not make it put out a lower voltage.... unless you burn it out into an open circuit, but few regard a 0V regulator as a desirable part.

Any way to remove potted epoxy from electronics ?