Mercury TV-220A restoration

[bandersen]

I replaced a few more out of spec resistors, reinstalled the tuner and twiddled with the controls a bit more.
Picture is better, but still not quite happy. I'm getting sound at two points - very noticeable when tuning the FM band.

So I figure I'll go through the alignment procedure. It looks pretty standard with a 21.25 MHz sound and 25.75 MHz video IF.


I managed to install a NOS cord by heating it up and mushing the ears over the rivets.
I don't have many of this type cord left. They used to be so common - never figured the supply would dry up


Also getting ready to recoat the CRT with some Slip Plate.

[bandersen]

CRT turned out nicely - still working on the alignment...

[Kamakiri]

What's this slip plate stuff?

[Electronic M]

Originally Posted by Kamakiri

What's this slip plate stuff?

Basically aquadag spray paint. If dag is flaking off it is one of the presently made/available products to re-coat/replace old dag with.

[Eric H]

I've been using this stuff to recoat, done three tubes with this can and it still feels nearly full.

Unlike Slip Plate. it makes a hard black coating that doesn't easily mar or rub off on your fingers.

It's quite conductive too, I measured the resistance from one side of a 14" tube to the other and it was about 2k.

You can get it on Amazon for about $16 if you have Amazon Prime.\

http://www.amazon.com/MG-Chemicals-C...uctive+coating

[Paul Knaack]

What sorts of symptoms would you notice if about 1/2 or 3/4 of of the dag coating were missing, even if all remaining dag were still grounded?

[Electronic M]

Dark patches on the screen from poor HV filtering and or noise on screen....Also rarely does a significant portion of the dag come off without "islands" forming, and the islands tend to arc to each other/other dag and grounds which may cause implosion....So far (knock on wood) I can't say I've seen a set with more than %10 (the most I'll tolerate before wanting to recoat) bad or lost dag. If dag damage ain't bad I eradicate dag islands and move on with my life.

[Paul Knaack]

Thanks Tom,

[Polaraligned]

I love how the slip plate makes my CRT's look like new.
The stuff Eric linked to looks pretty nice also. Looks closer to factory.

[Kevin Kuehn]

Originally Posted by Electronic M

Also rarely does a significant portion of the dag come off without "islands" forming, and the islands tend to arc to each other/other dag and grounds which may cause implosion

Is this really a well documented phenomenon, the resulting in implosion part? Don't recall ever reading about that before.

[Electronic M]

Originally Posted by Kevin Kuehn

Is this really a well documented phenomenon, the resulting in implosion part? Don't recall ever reading about that before.

I've read about ground strap arcing causing implosion, Zenith safety cap arcing (HV button to yoke) causing implosion, and I've heard of the islands arcing to each other. I don't know of any cases of island arcing causing implosion, but it is possible....Arcing generated intense local heat, uneven heat of glass causes fracturing, fracturing of glass under vacuum causes implosion.
I rather not risk it.

[Kevin Kuehn]

Agree it's best to error on the safe side. However my gut feeling is you'd be hard pressed to heat up an area of a CRT through conduction of it's dag coating, considering the typical resistance of the material and it's low thermal mass. Might be a fun youtube experiment.

[Electronic M]

Originally Posted by Kevin Kuehn

Agree it's best to error on the safe side. However my gut feeling is you'd be hard pressed to heat up an area of a CRT through conduction of it's dag coating, considering the typical resistance of the material and it's low thermal mass. Might be a fun youtube experiment.

It's not conductive heating of the dag at all. An arc essentially forms a super heated conductive plasma in the air to carry current. If you've ever experimented with high voltage arcs (like a Jacob's ladder or a plasma speaker or an automotive spark ignition system) you know that an arc generates enough heat to easily light paper, a cigarette, gasoline, and even burn/erode metal.

If you put your finger in the middle of a 20KV arc and you are not connected to either supply pole you will feel more pain from the plasma burn than the shock (as I know first hand).

[bandersen]

I got the recoated CRT installed without any troubles


I believe this chassis was originally designed for round CRTs because of a couple clues.
One - This tube bumps into the CRT and there's no room to install a shield.


Two - The discriminator coil is mounted under the chassis. That gave me a headache while doing the alignment as the instructions for adjusting the top and bottom slugs are the opposite of what I needed to do.
Sound is excellent now


I then fought with the ion trap magnet and centering rings to eliminate corner shadows and minimize distortion. Still not entirely happy, but it's not very noticeable while viewing programming.


So that's a wrap for the chassis restoration. Next up I'll arrange for a trip to reunite it with it's cabinet.

[decojoe67]

Originally Posted by bandersen

....So that's a wrap for the chassis restoration. Next up I'll arrange for a trip to reunite it with it's cabinet.

Very nice Bob. You do superior work!