Questions about 19AP4

[Jon1967us]

1. Can I use a 10BP4 as a test CRT, instead of the 19AP4, on a Zenith porthole chassis? The pinout appears the same. I know I would need to elevate and stabilize the 10" if I want to use the 19ap4's yoke and ion trap. I don't expect a great picture, I just want to validate a raster and deflection.

19ap4 https://frank.pocnet.net/sheets/127/1/19AP4.pdf

10Bp4 https://bms.isjtr.ro/sheets/127/1/10BP4.pdf

2. When using the 19AP4 toward the (hopefully) final stages of circuit restoration, is the method of discharging the CRT to ground the metal flange? I wish to avoid getting zapped in case I bump or handle the CRT after use.

[Notimetolooz]

I don't think metal bell CRT store as much charge as the glass ones. The glass CRT use the glass bell as a smoothing capacitor, one plate is a coating inside that is connected to the TV HV. A coating on the outside forms the grounded second plate. The TV that use a metal CRT have capacitors as part of the HV circuit, those store a charge that you should discharge to ground, by connecting the bell to ground. So if you use the 10BP4 make sure both the anode button and the ceramic HV caps are discharged.

[Jon1967us]

Originally Posted by Notimetolooz

I don't think metal bell CRT store as much charge as the glass ones. The glass CRT use the glass bell as a smoothing capacitor, one plate is a coating inside that is connected to the TV HV. A coating on the outside forms the grounded second plate. The TV that use a metal CRT have capacitors as part of the HV circuit, those store a charge that you should discharge to ground, by connecting the bell to ground. So if you use the 10BP4 make sure both the anode button and the ceramic HV caps are discharged.

Are you talking about the doorknob 500pF cap that the 1b3 inside the HV cage sits on? I didn't know that could store a charge being such low capacitance.

What would be the best way to make an adapter for the anode lead? I have a spare anode lead with suction cup. What would be the safest way to couple that with the existing single prong anode lead for connection to the 10BP4?

[Electronic M]

Originally Posted by Jon1967us

Are you talking about the doorknob 500pF cap that the 1b3 inside the HV cage sits on? I didn't know that could store a charge being such low capacitance.

What would be the best way to make an adapter for the anode lead? I have a spare anode lead with suction cup. What would be the safest way to couple that with the existing single prong anode lead for connection to the 10BP4?

If you are planning to do that test jiging for a prolonged period I'd pr unsolder the original lead from the HV rect base and solder the modern HV lead in then after your done switch back.

I think the proper test CRT is a 5AXP4 btw.

[Notimetolooz]

Originally Posted by Jon1967us

Are you talking about the doorknob 500pF cap that the 1b3 inside the HV cage sits on? I didn't know that could store a charge being such low capacitance.

What would be the best way to make an adapter for the anode lead? I have a spare anode lead with suction cup. What would be the safest way to couple that with the existing single prong anode lead for connection to the 10BP4?

Yes the door knobs are those caps. The ceramic caps do have a bit more leakage than the glass dielectric of the tube but the capacitance of the tube is usually stated as being about 500 uuf (pf).
I have some people put an alligator clip on the extension and place the joint in a glass jar to insulate it.

[Jon1967us]

Originally Posted by Electronic M

If you are planning to do that test jiging for a prolonged period I'd pr unsolder the original lead from the HV rect base and solder the modern HV lead in then after your done switch back.

I think the proper test CRT is a 5AXP4 btw.

Good call. And I think you're right the 5AXP4 is the correct test CRT. I suspect the 10BP isn't quite compatible.

[bandersen]

Pretty much all the early 12 pin CRTs have the same pin out and similar specs. The 10BP4 will work but you may be pushing the HV a little hard.

I believe you could also rig up a 5PF7 radar CRT in a pinch. The phosphor will be weird, but they're cheap and work fine for initial power up and troubleshooting.

[Jon1967us]

Originally Posted by bandersen

Pretty much all the early 12 pin CRTs have the same pin out and similar specs. The 10BP4 will work but you may be pushing the HV a little hard.

I believe you could also rig up a 5PF7 radar CRT in a pinch. The phosphor will be weird, but they're cheap and work fine for initial power up and troubleshooting.

Cool. Unfortunately I do not own either a 5axp4 or 5pf7. Will need to study the 10bp4 data sheet to see if HV and other voltages would be tolerable I suppose. Otherwise, I’ll just need to be extra careful testing with the rather unwieldy 19ap4 on my bench.

I’m mostly concerned about safety when handling the crt in and out of the chassis after being charged - where/how to discharge the metal cone crt and make sure I don’t get bit.

[Notimetolooz]

You would of course discharge it before you disconnected it.

[Kevin Kuehn]

An old school high voltage prob works well for discharging plus you'll know how much high voltage your set is producing.

[Jon1967us]

Originally Posted by bandersen

Pretty much all the early 12 pin CRTs have the same pin out and similar specs. The 10BP4 will work but you may be pushing the HV a little hard.

I believe you could also rig up a 5PF7 radar CRT in a pinch. The phosphor will be weird, but they're cheap and work fine for initial power up and troubleshooting.

Could it be a 5FP7?

[AdamAnt316]

Originally Posted by Jon1967us

Could it be a 5FP7?

That's what he meant. Older CRTs (almost?) always have 'P' as the last letter in the designation, followd by a number, to denote the type of phosphor used. A full list can be found here, but the ones most of us are likely to run across are as follows:

P1: Green, medium persistence (used in oscilloscopes, some green monochrome monitors)
P3: Orange, medium persistence (used in amber monochrome monitors, apparently)
P4: Bluish-white, medium persistence (used in black & white TVs)
P7: White/yellow, short/long persistence (used in old radar equipment)
P22: Red/green/blue, medium persistence (used in color TVs, of course)