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

[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

[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?

[jr_tech]

I think that a bit of extra filtering likely would not cause a problem with the HV supply, BUT the HV would pack a greater punch if you should get across it.

jr

[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

[radio nut]

Well Jr Tech....You were right! On Sunday I went back to the diagram and sure enough it calls for a coating on the crt. Well, I do have a really strong crt with an intact coating to put in it and I did. I also added a ground connection.
The tv has a really good picture now plus it has the shut off dot! Now the sound has a loud type of hum so I will have to readjust the sound trap and see what happens.

[Reece]

It is possible for you to put a new coating on yourself. I forget the name of the product but it has been mentioned on the forum before. Someone will know the name of it.

[lnx64]

Slip-plate?

[Phil Nelson]

Another good product for replacing aquadag is Aerodag G. Easy to spray on, and it dries in a few minutes.

Phil Nelson