21zp4a crt sub

[timmy]

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.

[bandersen]

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

[kvflyer]

Originally Posted by Electronic M

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

[timmy]

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.

[kf4rca]

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.

[timmy]

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

[bandersen]

No. Ceramic and very stable

[Yamamaya42]

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.

[timmy]

Originally Posted by Yamamaya42

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.

[bandersen]

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.

[timmy]

Originally Posted by bandersen

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.

[bandersen]

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.

[timmy]

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.

[kf4rca]

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]

Originally Posted by kf4rca

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.