Got a lead on an early DuMont TV locally

[vortalexfan]

Unfortunately I have a sad update on this old DuMont TV, The 19AP4 Tube is a dud, I went to try and test it with my old picture tube tester and the tube filiments weren't glowing, so I'm guessing the tube must of went to air...

[Electronic M]

Originally Posted by vortalexfan

Unfortunately I have a sad update on this old DuMont TV, The 19AP4 Tube is a dud, I went to try and test it with my old picture tube tester and the tube filiments weren't glowing, so I'm guessing the tube must of went to air...

Before you declare it dead check the heater pins for continuity. Sometimes the solder in the pins fails or the wire outside the glass corrodes open...Both are usually fixable (the latter with a fair bit more effort than the former). If you have heater continuity and with 6.3V applied it doesn't glow but the neck gets very warm very fast then you can be confident it's gassy.

[vortalexfan]

Originally Posted by Electronic M

Before you declare it dead check the heater pins for continuity. Sometimes the solder in the pins fails or the wire outside the glass corrodes open...Both are usually fixable (the latter with a fair bit more effort than the former). If you have heater continuity and with 6.3V applied it doesn't glow but the neck gets very warm very fast then you can be confident it's gassy.

OK, Thanks I'll give that a try. If the Picture tube is indeed a dud, I'm guessing that means I'm going to have to give up on this TV? I say that because I don't want to buy a picture tube for this TV if its going to cost me over $100 and if there's a risk that the tube might fail during shipping.

[Jeff]

Originally Posted by vortalexfan

OK, Thanks I'll give that a try. If the Picture tube is indeed a dud, I'm guessing that means I'm going to have to give up on this TV? I say that because I don't want to buy a picture tube for this TV if its going to cost me over $100 and if there's a risk that the tube might fail during shipping.

I'm sorry nobody warned you about metal cone picture tubes often going to air, I guess to some it's such common knowledge they forget to mention it.

[vortalexfan]

Yeah, Unfortunately I think this picture tube is a lost cause, because I checked it for continuity and it wouldn't respond to my DMM, it just read "OL".

[Chris K]

I feel for you my friend. I've got an RCA cabinet model in beautiful condition with a just about dead 16GP4 metal cone CRT. The availability of these CRTs is a bit higher but still hard to find in good condition.

[vortalexfan]

Is there any way to modify this set to get it to work with a picture tube that isn't of the metal cone variety?

[Jeff]

Originally Posted by vortalexfan

Is there any way to modify this set to get it to work with a picture tube that isn't of the metal cone variety?

I would assume if you can find an early 50s 19 or 21 inch tube that has the same socket, and you're willing to mount it, all that would be left to deal with would be the what the earlier yoke would do on a later tube... which means, if you simply plug a later tube in and stick the yoke on it, it might not fill the entire screen? Someone may have to correct me on that...

You could use the yoke for the later tube, but if it doesn't just "work", then science and math are involved, yuck!

[Electronic M]

Originally Posted by vortalexfan

Is there any way to modify this set to get it to work with a picture tube that isn't of the metal cone variety?

There's several points Jeff is off on but, instead of poking holes I'm going to approach this as a rough how to guide.

When it comes to magnetic deflection CRTs the guns and bases were basically all the same between 1946 and 57. Ignoring glass cone VS Metal (which is more of a mechanical mounting and HV lead conversion process) there's 3 major things to consider in selecting an all glass replacement:
1.) Deflection angle: there were 3 main angles in that era ~60 degrees, ~90 Degrees, and ~110 degrees. Use the datasheet to figure out what angle your tube has and what your replacement candidates are. There were some in-between angles too. Jumping from a 60 to a 90 isn't a great idea but a 72 could probably work in either of the previous 2 angles.
2.) Focus type: some tubes are magnetic focus and others are magnetic. It's easiest to use a tube of the same type, but you can work around it by adding or deleting a purpose built focus magnet and sometimes adding focus voltage taps.
3.) screen size: you can technically fit any size CRT of the same deflection angle and focus type right into a set and make it work. Some companies used the same chassis without any changes to drive a 10BP4, 12LP4 or a 16AP4 (there were even some larger compatible tubes) depending on what screen size model was being made.... However if doing a modification and using the original mask you need something that fills the mask but fits the cabinet. A 24" tube in a 16" cabinet isn't going to work and a 10" tube in a 16" cabinet will look wrong.... Besides the obvious there can be issues with different dimensions between the neck shoulder and screen requiring the yoke mounting brackets to be moved, and a glass bell flaring out wider than a metal one and interfering with the chassis...

These are all problems that will vary widely depending on the model and tube you want to pair up. Most are not insurmountable, but picking the most compatible tube possible is important for minimizing headaches.

[Alex KL-1]

Absolutely well pointed by Electronic_M. Using same logic I subbed the CRT of a '60 Brazilian Admiral for another brand and model CRT. Paying attention to mechanical drawings and electrical limits/deflection angle (most are 110 or 114 degrees from that era).

[Jeff]

Originally Posted by Electronic M

There's several points Jeff is off on