21zp4a crt sub

[kf4rca]

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 It was superseded by the Chyron which could do graphics.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.

[bandersen]

Does this match your set?

Riders vol 13, chassis


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?

[bandersen]

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

[timmy]

Originally Posted by bandersen

Does this match your set?

Riders vol 13, chassis


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?

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.

[timmy]

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

[bandersen]

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.

[timmy]

Originally Posted by bandersen

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 ?

[Electronic M]

Originally Posted by bandersen

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

[timmy]

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

[timmy]

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.

[kf4rca]

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.

[Electronic M]

Originally Posted by timmy

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.

[timmy]

Originally Posted by Electronic M

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 ?

[Yamamaya42]

Originally Posted by timmy

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/tec...pacitor-types/

[Electronic M]

Originally Posted by timmy

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.