Using an 8YP4 in a Predicta (17DRP4) ?

[bandersen]

Hi guys,

Has anyone managed to rig up an 8YP4 so it can substitute for 17DRP4? I think that the only issue is the filament voltage. Maybe adding a few D-Cells to boost it?

P.S.

Anyone know where I can get a 5AXP4 ? I'm putting my workshop together and I had no idea these little test CRTs existed. They're awesome!

[pallophotophone]

Originally Posted by bandersen

Hi guys,

Has anyone managed to rig up an 8YP4 so it can substitute for 17DRP4? I think that the only issue is the filament voltage. Maybe adding a few D-Cells to boost it?

P.S.

Anyone know where I can get a 5AXP4 ? I'm putting my workshop together and I had no idea these little test CRTs existed. They're awesome!

It won't work as the filament is fed AC. I'd just use an outboard 6.3 volt transformer or dc power supply. It'll be fine with either AC or DC feeding the filament.
And if the set uses a series filament string (that is to say the set doesn't have a power transformer),you'll have to complete the string to maintain filament voltage to the other filaments.

Best !

Bob Hodge

[Don Lindsly]

You will need the correct socket adaptor to go from the Sylvania type on the CRT to the Philco type on the Predicta socket. That has different pin connections from the more popular RCA socket that looks the same. I believe the Philco adaptor socket exchanges the screen and control grids.

The filament current and voltages are different on the Philco tube.

In a series set, the 8YP4 will work OK with the right adaptor socket. It will just take a little longer to warm up to full brightness.

In a transformer powered version, you can jumper the dropping resistor, if used. If it uses a 2.6 volt transformer tap, you can move the CRT filament power to the 6 volt buss TEMPORARILY. Use a clip lead and move it back before reconnecting the 17DRP4.

Don

[kx250rider]

Won't the yoke impedance be all wrong, as you can't use the smaller 17DRP4 yoke... You'd have to use a duodecal base type yoke, which will be 70 degrees max, if I'm correct, and won't match the Philco flyback and vertical output transformers. I'd get a smaller button-base tube, maybe a 12" tube out of a cheapie 60s portable, and then all you have to do is rewire the socket and feed it 6.3 from an outside source.

Charles

[bandersen]

Thanks for all the great info. It is a transformer set and the CRT filament has it's own winding. The Predicta yoke fits just fine and I do have an adaptor socket, but I'll be sure to double check the wiring. Here's a picture of my setup.

[Don Lindsly]

The setup in your picture will work fine. Just temporarily move the CRT filament connection to the 6 volt filament source for testing with the 8YP4. ]

Make sure you move it back before connectiing the original tube.

All Philco yokes of that era are electrically similar. Some plugs are wired differently. A test set can be made to accommodate all the black and white sets. It requires some switching and adaptor plugs for various chassis configurations.

Using the original yoke will present no problems.

Good luck,

Don

[bandersen]

Thanks, Don. The filament is glowing nicely now, but I've got another problem. There's a strong smell of ozone coming from the CRT/yoke area. There's no sound or visible arc in the dark. I'm thinking that the lack of external aquadag could be an issue. That wire hoop in my picture makes contact to the dag on the original tube. Maybe I should just hook up the original CRT after all ?

[Don Lindsly]

Check inside the high voltage cage. The anode lead plug in the 1G3 socket could be loose. A strong ozone smell should show up somewhere in the dark.

You may get some erratic effects from no aquadag ground on the CRT, but don't worry about it. Fix everything else using the test tube. I avoid fooling with large and/or rare CRTs on the bench.

I have glued some foil or silver duct tape to a couple of my test CRTs to provide a ground. The coating was left off of the test CRTs purposely to avoid shorting out to chassis components. You don't need to cover much of the tube to form a capacitor.

Don

[bandersen]

Great idea about the foil. I haven't done any poking around inside the cage yet, but that seems like a likely culprit. I did get a few flashes of life from the 8YP4 last time i fired it up so I'm optimistic.