CRT experts please

[radio nut]

The Muntz tv that I recently posted about has a 16RP4 picture tube. It does not have an aquadag or any metal piece (grounding strap) touching the crt.
Plus there was not any flaky aquadag material on the chassis, at all.
The tv came from my best friend's Mother's house and no one in recent history messed with it.

I came across two other tv's that use the same crt and both have an aquadag and a grounding strap.

The crt in the muntz is weak and needs replaced.

Well, Just swap or what do I need to do to be safe?

[stromberg6]

Perhaps there is a filter cap in the high voltage cage under or around the 1B3. Agreed that it's strange that other tubes of that type have aquadag and yours doesn't. Only had one Muntz in my life, and it was a later model with a 21" tube, a two IF urban special. What's your model or chassis number? Maybe someone with Rider TV books or SAMS can look it up to find out how it was configured. Good Luck! Sounds like an interesting challenge.

[stromberg6]

Just found this online. It says that there is supposed to be a coating. Hope it helps!
Kevin

[radio nut]

Originally Posted by stromberg6

Perhaps there is a filter cap in the high voltage cage under or around the 1B3. Agreed that it's strange that other tubes of that type have aquadag and yours doesn't. Only had one Muntz in my life, and it was a later model with a 21" tube, a two IF urban special. What's your model or chassis number? Maybe someone with Rider TV books or SAMS can look it up to find out how it was configured. Good Luck! Sounds like an interesting challenge.

Yes there is a high voltage cap below the high v rectifier...... Like you, I too looked up the 16rp4 specs and yes it shows a coating....

But this muntz is working....no coating on crt or grounding strap.........no where on chassis...now what. use another crt and put my own grounding strap on or what. I will recheck what model number it is and post it here.I just dont know which way to go,The set works well but the crt is weak and has the classic "indian" test pattern burned onto the screen....... So I would like to do something

[earlyfilm]

Originally Posted by radio nut

. . . the crt is weak and has the classic "indian" test pattern burned onto the screen. . . . .

Sheesh! I don't think I've ever seen test pattern burns except on TV station monitors, and no TV station would use a Muntz!

(Well, I once worked at a TV station that had Crosley monitors in the Lobby, but WLW-A, now WXIA, was owned by AVCO at the time, and boy, did they go away the moment the station was sold.)


On the conductive coating, a more logical guess is that someone cleaned off the old flaking paint not realizing that it was part of the tube.

However, I've seen a few rebuilt CRTs that had an external conductive coating where one was not specified (and if they do, you must fabricate a ground or it will bite you) and much more commonly, a new-out-of-the-box rebuilt CRT that was missing the coating.

A peculiarity of the CRT that you have is both the 16RP4 and 16RP4A require an ion trap while the 16RP4B does not! Back in the late 50's I replaced a CRT, I can't remember the tube number, but it was an all glass B&W roundie, where this tripped me up, and the rebuilt tube actually looked dimmer than the one it replaced until my boss removed the old ion trap that I had transferred to the new CRT! I felt like an idiot for not catching this, and he never let me forget it. I noticed the ion trap never had a brightest spot, even if reversed, and that should have been a clue, but I slept through it.

James

[earlyfilm]

Originally Posted by radio nut

. . . . . . . . . . .Yes there is a high voltage cap below the high v rectifier . . . . . . . . .

The most common basic 1951 Muntz chassis was used in set model M31 and a bunch of other adjacent numbers indicating cabinet variations . The M31 schematic in Beitman's 1951 page 101 does NOT show a 500mmF underneath the 1B3, but it does show an aquadag coating on the CRT. To lessen horizontal streaking on a CRT one needs some HV capacitance. This could be either an early repairman's fix or a factory modification to use some 16DP4A's that Muntz or the repairman happened to have.

When one looks at the three alternate CRTs used with this chassis, one will see both the 19DP4A and 16RP4A carry an aquadag coating while the 16DP4A has no aquadag! So, this chassis could be a production line substitution where Muntz used a different CRT that they purchased for a few cents less than the cost of a 500mmF doorknob, or it could be just a serviceman's replacement CRT because he could not quickly locate a correct tube.

Jas.

[radio nut]

It is Sam's 108-8 for sure.... 16a2 model number "M31" I think.

But it is Sam's number 108-8.

[jr_tech]

An ancient GE tube manual that I have says the coating provides 750-1500 uuf of capacitance... how big is the capacitor in the HV cage?

jr

[radio nut]

I """think"""" 500uuf......

Could Muntz for this set have ordered uncoated crt's?
I am very sure that the diagram does NOT show a line from the crt coating to ground.

But It calls for a 16rp4 crt.

I could scrub the coating from the extra crt......but.....that just does not seem right.
I had my friend check and there is NOT a grounding strap or stiff wire touching the crt anywhere, or something broke off that could be it.

[jr_tech]

I have a slightly later photofact, #116, folder 10 for a M31,32,33 Muntz using a 16RP4. The grounded coating is clearly shown, but there is no cap shown in the HV cage. The grounding for the dag is provided by a "finger" about 1/2 inch wide and about 3 inches long mounted at the top center of the yoke mounting plate... check above the yoke for a hole or broken "finger"

jr

[dieseljeep]

[QUOTE=radio nut;3053511]I """think"""" 500uuf......

Could Muntz for this set have ordered uncoated crt's?
I am very sure that the diagram does NOT show a line from the crt coating to ground.

But It calls for a 16rp4 crt.

I have a 20" Muntz, where the CRT was necked. I removed the broken CRT and trashcanned it. I don't remember seing a aquadag coating on it. I also remember seeing other Muntz's without it as well.
The tube had a rubber stamping stating: American Television, Chicago,Il.
IIRC, Those CRT's, had a slightly bluish white phosphor, when compared to other sets next to it.

[wa2ise]

On a CRT with missing 'dag, would using aluminum foil glued to the outside where the 'dag should be work? Of course such foil would be grounded.

[bandersen]

Originally Posted by wa2ise

On a CRT with missing 'dag, would using aluminum foil glued to the outside where the 'dag should be work? Of course such foil would be grounded.

Sure, I've done that a few times

[radio nut]

[QUOTE=dieseljeep;3053944]

Originally Posted by radio nut

I """think"""" 500uuf......

Could Muntz for this set have ordered uncoated crt's?
I am very sure that the diagram does NOT show a line from the crt coating to ground.

But It calls for a 16rp4 crt.

I have a 20" Muntz, where the CRT was necked. I removed the broken CRT and trashcanned it. I don't remember seing a aquadag coating on it. I also remember seeing other Muntz's without it as well.
The tube had a rubber stamping stating: American Television, Chicago,Il.
IIRC, Those CRT's, had a slightly bluish white phosphor, when compared to other sets next to it.

The original crt had american television on it also...But It had to be cheaply made, the phosphor did not even cover the entire front screen area . on the top right side there is a section about one quarter of an inch tall that is uncoated

[radio nut]

Ok, will do.
Out of curiousity since I have only repaired about 7 tv's so far and do not remember the others to well It is possible to have high voltage cap and coated crt?