Admiral 19A11
 

This is my first television after many successful radio restorations. I have replaced the 6000 volt caps and the electrolytic. On my variac I get a nice bright raster at about 85 volts. I’m afraid to go any higher because I also get a spark that seems to come from the case of the horizontal centering control. The spark will repeat every couple of minutes and during the split second of the spark the raster disappears. I’d like to know where I might go next. Thanks.

Have you tried cleaning the pot of any debris or tin whiskers?

.

Make sure that no sharp points were created by cutting the wires of the new parts.

And also make sure that the insulated board that the hv pots are mounted on is clean and free of carbon tracks.

Can you see where the arc occurs in a darkened room?

jr

I have not. The control is soldered directly to another pot and I'm going to have to think through this a bit so I don't wreck it.

I had my daughter help me make a video of the arcing. I may post it but I'm not sure it shows up clearly enough. However, I'm convinced now that the arcing is occurring inside the control. As I mentioned in another reply, this control is soldered directly to another pot and I'm going to have think through this a bit. I may need to order some new solder wicking too. Is there any possibility of a repair on something like this?

Remove the leads from the pot. (you can keep the terminal heated and the solder molten and coax the wire out with needle nose pliers...unless a terminal is especially delicate I don't bother removing the old solder) Remove the pot from the chassis. the front will be phenolic with the metal shaft collar and a metal plate covering most of the phenolic. The back cap of the pot will have ~4 fingers that fold over the front metal plate to hold the pot together, pry up those fingers (a very fine flathead screwdriver or dental pick is god for this) and it should all pull apart. Clean the inside thouroughly with an old discarded tooth brush and some control cleaner, then come back with paper towel and or Q tips and more control cleaner. Once it looks spotless reassemble in reverse order.

If there has been a lot of arcing and it has carbonized the phenolic, try and scratch it off.

Actually if it's arcing inside the pot, the resistance wire winding inside is likely broken. Open to look anyway.

Unrelated, what is the radio in your avatar? I have one that looks exactly like it... except it's a 1970s reproduction and it's made of plastic. lol

I’m going to open the pot today. I hope it’s not broken.
My avatar is a Philco model 90 from the early 1930’s that I restored.

Isn't the set they are working on electrostatic? Electrostatic sets typically use all carbon comp potentiometers because none of the control circuits are high current/power. Wire rheostats are typically limited to high current applications like electromagnetic focus, centering, and cathode resistance vertical linearly in mag deflection sets.

I got it apart. It's carbon. I don't see any burned or damaged areas. I'll clean it with deoxit, replace the two resistors attached to it that have drifted high in value and then reinstall. Wish me luck.

I reinstalled the control and everything seemed to be ok. For a while I had sound and a picture. The picture was out of focus but stable. Then something arced again and the raster disappeared. I guess I no longer have any high voltage. If anyone has thoughts or ideas they would be most appreciated.

It’s working pretty well now. Still May need to replace some resistors and I can’t figure out why the vertical linearity control does nothing.

I still don’t have enough vertical. It’s especially noticeable now that the chassis is back in the cabinet. I’ve replaced everything I can think of. Unless someone has an idea I’m going to move on to the next project. The set is watchable but it should definitely have more height.

Steve Chambersl

With those 60 year old potentiometers, tin whiskers may have formed causing a short around the terminals of the control or even inside. If you can get access and scrub the outside of the control, if it is tin whiskers, it may fix it. That was the problem with my Admiral 26R12 set. Adjusting the vertical linearity did nothing and the clue (which I missed!) was that adjusting the control made no difference on the voltage.

If you used ceramic caps to replace the 6kv caps instead of the proper film type caps then there's your problem.