Philco 51-PT1207 picture tube question

[kramden66]

Anyone know if it is possible to put a 12LP4 crt in one of these sets ? I know someone with one but the crt has a crack and a hole at the neck , i glanced and it looked like you could fit the larger neck in that focus magnet but unsure about the yoke and the bell size , anyway thought i'd ask for those who would know or have one ( I Think Eric H has one )

thanks
Mike

[Eric H]

I've been told that you can and that it has been done before.

You have to change the Yoke of course, and the tube socket.
The front may have a different curvature but not by much I don't think, not sure about the length but it seems about as long as any other Philco of the time.

I believe the basic chassis is used in other sets with a conventional tube.

They are a neat little set, this one's running on it's original tube.

[Don Lindsly]

It is possible to install a 12LP4 in a 51-PT1207/8. A 12KP4 is a better choice since it does not require an ion trap or modifying the CRT cup on the back.

Either tube requires more deflection current so a few circuit mods are necessary to get a full picture. If decide to make the change, I can provide a list of changes and part numbers to save you some time.

That chassis was unique to the PT1207/8 series. It included some engineering advances, but the basic chassis design was not extended to other products. Philco did not use a series string again until the 1957 portables.

It will require a new flyback, obviously a yoke, vertical output tube and filament circuit rewiring for a start.

[kramden66]

Wow a new fly and other things , sounds like a lot to do.

mike

[Don Lindsly]

Mike:

Yes, there's a lot to do. The most difficult is finding a new/good 12KP4. Without that, the rest is futile. I started with a new CRT and had the rest of the parts on hand.

Eric's set has a great picture for the original tube. Typically, the tubes were more likely to break than burn out. Necks would crack from overheating and the side evacuation pinch off would crack.

The tube did prove the concept of thin neck, low deflection current, no screen grid, light weight and edge to edge focus.

Don

[kramden66]

Eric H , the picture looks nice and i can hear it " Hey Ralph these guys are from the investment firm i was telling you about "

mike

[kramden66]

so you can't use a 12lp4 with a ion trap ?

mike

[Electrohome]

The above post is spam-please remove-Thanks.

[Eric H]

Originally Posted by Electrohome

The above post is spam-please remove-Thanks.

Done.

[Don Lindsly]

Mike:

You can use a 12LP4. The metal cup will slightly "detune" the ion trap when the back is put on. You will also need an ion trap and CRT socket that will clear the small CRT cup or replace the cup with something larger. Don

[kramden66]

But what i see is if you have to replace the yoke where do you get the yoke ? also change vertical tube and fly , etc etc , is the yoke inside a different deflection angle or is the center just too small , i saw that the focus magnet seemed to have a large hole simular to 12lp4, its too bad you just can't put the 12lp4 in.

mike

[Don Lindsly]

The focus magnet is the same as used on several other Philco sets of the era. The yoke is unique to the 1207/8 to fit around the narrow neck CRT.

Most early 50s Philco yokes, part # 32-9622, 32-9628, will work. You will need to make a couple of wiring changes using the original cable and plug. The horizontal center tap must be brought out to the flyback tap to correct mismatch.