Help wanted resurrecting 1969 Zenith 12A10C15

[Freon]

Originally Posted by old_tv_nut

Yes, the cup is the white plastic, well, cup that the tube is in. Don't be afraid to wash things, with a damp rag and dish soap for example. Rinse with a damp cloth and air dry or use a hair dryer.

Well, if you say so... Quite an improvement, no? I decided to get rid of the tape, I could always put some back on if I have to.

Originally Posted by Electronic M

Once you've cleaned or perhaps before you clean it is wise to run the set briefly to find the exact spot it is arcing, and or better localize it so you can fix that easier/better.

Do you suggest I try running the set with the cabinet off and maybe even the HV cage open? Definitely too afraid to do that, especially on a carpet floor. I could clear up a table for it, though.

Does anyone know if that 6LF6 I mentioned will be alright? I hope so, it's an expensive replacement. Speaking of tubes, the 6U10 looks like it is barely holding on... looks like almost all of the getter coating is burnt off. Thankfully THAT's a dirt cheap replacement. I will check the 3DB3/3DC3 tomorrow. It won't budge so Im guessing I will have to unscrew the cup first?

[Electronic M]

Originally Posted by Freon

Do you suggest I try running the set with the cabinet off and maybe even the HV cage open? Definitely too afraid to do that, especially on a carpet floor. I could clear up a table for it, though.

Does anyone know if that 6LF6 I mentioned will be alright? I hope so, it's an expensive replacement. Speaking of tubes, the 6U10 looks like it is barely holding on... looks like almost all of the getter coating is burnt off. Thankfully THAT's a dirt cheap replacement. I will check the 3DB3/3DC3 tomorrow. It won't budge so Im guessing I will have to unscrew the cup first?

That is exactly what I suggest. Once you loose count of the times HV has bit you (as I have ) you'll still avoid it and respect it, but the fear will fade away.

Unless the plate (large outer element) starts to glow in the dark or the tube arcs internally, if you still have healthy amounts of HV and decent raster width the tube is fine. It can handle the extra load of HV arcing reasonably well...The set that I had to drill out a carbon track from the HV cup on was arcing so bad the raster would disappear from the HV loading down, but the H output tube was fine....Even if your set was worse under 30 seconds of active arcing should not hurt it appreciably....When the going gets tough transistors die instantly, but tubes begrudgingly muddle on for a few minutes before biting it.

Madman: welcome to the world of late 60's-mid 70's hybrid TV chassis. Ever work on a set where there are ~12 tubes about as many discrete transistors, and a DIP IC....All chassis mounted?...I have. The makers had some STRANGE component combos in that transitional era. I know of an instant on knob tuned remote controlled set with tube based sweep and an OSD generated by a large DIP chip. Part of the fun of working on the later sets that the big money collectors scoff at is that you get to see some unique things that you'd never expect to see paired up.

[zeno]

The HV cups were high failure rate on these & the 16"
cousin. Would get pin holes. Also filament windings would
arc. Fire it up with the door opened to see where its arcing.

Disassembly:
First discharge the HV several times. If the tube wont
budge it may be rusted in. Remove the separate plastic
part of the socket ( pull up) then the 2 screws holding in the socket
then the cup. Clean up & fix the arc.
Remember that all the HV & wiring is sitting as apx 22KV so
any rewire needs high breakdown wire.

73 Zeno
LFOD !

[Freon]

Originally Posted by zeno

The HV cups were high failure rate on these & the 16"
cousin. Would get pin holes. Also filament windings would
arc. Fire it up with the door opened to see where its arcing.

Disassembly:
First discharge the HV several times. If the tube wont
budge it may be rusted in. Remove the separate plastic
part of the socket ( pull up) then the 2 screws holding in the socket
then the cup. Clean up & fix the arc.
Remember that all the HV & wiring is sitting as apx 22KV so
any rewire needs high breakdown wire.

73 Zeno
LFOD !

So, just to make sure, I should be able to pull out the tube without unscrewing anything?

Also, any special procedure for removing the cap thing on top of the tube? Is it attached by metal hooks like the anode cap or do I just pop it off?

[Freon]

Well, Electronic M and Zeno were right on the money. The cup's got two holes on the bottom of it (but just one in practice as you'll see), and someone obviously attempted a repair.
More electrical tape under cup
One of the holes filled with black goop
Bottom of cup
Not only that, but one of the screws holding the cup to chassis is missing.
Doesn't seem like something a tech would do. I'd almost guess an enthusiast tinkered with this one not too long ago, and perhaps decided it was beyond saving... Or, more than likely, the second hole is fresh and unrepaired.
Looks like I'm gonna have to figure out how to use silicone... Or anywhere I can just buy a new one...?

[Kevin Kuehn]

That's a really interesting TV. I believe the tubes remained so late in the game because Zenith engineers felt they were still considered the most reliable components for their specific circuit functions.