21zp4a crt sub

[timmy]

Any idea for a substitute crt for a 21zp4a ?

[bandersen]

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

[timmy]

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

[bandersen]

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

[timmy]

Originally Posted by bandersen

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

[Electronic M]

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.

[timmy]

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

[bandersen]

Assuming it is electromagnetic, like this.


If it's a permanent magnet type. Like this.

[timmy]

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

[bandersen]

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

[timmy]

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

[bandersen]

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.

[timmy]

It’s a 1954 cbs Columbia 21 inch

[Electronic M]

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.

[timmy]

Any knowledge on who built the chassis for cbs Columbia?