Stabilizing a TS-18

[Zenith26kc20]

This weekend revealed a problem I have never seen before. The vertical centering control had gone down to 1 megohm. This disabled both horizontal and vertical centering! I pulled the leads loose connecting the two controls and ohmed them out, the vertical being low. I went so far as to pull the control to be sure it was down in value. It is still linear thru it's range and the tap is correct in being half (.5 meg) on each side of the control. I put some 1 meg fixed resistors in place of the control and the horizontal centering works great. I may try adding one 470k resistor in each leg of the control to bring it back to 2 megohms. If the centering is adjustable enough (right now, with the fixed resistors it's nealy perfect) I may just leave it like that.
Now the snowy picture has to be tackled!
Oh, that is my test 7 inch CRT. I am very careful with the 8 inch. That one came from the bakelite TS-18 that is really nasty. Someone put some green plastic to hold the CRT in place and it melted everywhere. It took me an hour to scrape the bell and face clean. It's a Philco tube and it is in great shape!

[Zenith26kc20]

Last night I reinstalled the vertical centering control with the added 470 k resistors and now all the centering problems are cured. The next thing was what appeared as a snowy picture. I went to check the 6AG5 and discovered a 6AU6 in it's place. My tube tester calls for a lock out on the 6AG5 pin two, no lockout on the 6AU6. Installing a 6AG5 gave me a picture better on this set than my other two! I'm still using the 7 inch tube but to say the least, spectacular!
Stabilizing the picture seems to be more related to the sweep tubes. Older types seem to drift more than newer. The vertical is dead stabile. The horizontal is to the point where it locks in about 25 seconds once raster appears and requires one adjustment in about 30 minutes.
Tonight starts the sound circuit repairs!
And more pictures!

[Eric H]

Originally Posted by Zenith26kc20

That one came from the bakelite TS-18 that is really nasty. Someone put some green plastic to hold the CRT in place and it melted everywhere. It took me an hour to scrape the bell and face clean. It's a Philco tube and it is in great shape!

I would bet it's the melted gasket from the Motorola, they are famous for that.
Plain old water will wash it off.

[Zenith26kc20]

I wish it was the grey colored goo but it was bright green where the easy melt was. The nasty part was where it turned black and rock like.
Anyway, the Colonial/Sivertone has the bench before that one so I have plenty of time to scrape and watch TV while I'm not replacing the million capacitors in the Colonial.
By the way, here's the picture of the chassis playing about two minutes after turn on!
Love the little electrostatic critters!