21zp4a crt sub

[timmy]

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.

[timmy]

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.

[timmy]

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.

[old_tv_nut]

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.

[timmy]

Originally Posted by old_tv_nut

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.

[timmy]

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

[bandersen]

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?

[timmy]

Originally Posted by bandersen

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.

[timmy]

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

[bandersen]

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

[timmy]

Originally Posted by bandersen

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

[timmy]

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.

[timmy]

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

[kf4rca]

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!

[Electronic M]

Originally Posted by timmy

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.