21zp4a crt sub
 

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

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/5581/1...623e01c2_c.jpg

If it's a permanent magnet type. Like this.
https://live.staticflickr.com/587/21...221e6a00_c.jpg

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.

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?

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

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!

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/...da8a119c_c.jpg

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/...e669d36e_b.jpg

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

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 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 ?

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.