Convergence ?
 

Is there any definitive reason why a perfect convergence is obtained but after a few months it goes out of where it was previously. Never moving the set. Or is this just 60s technology just not perfect.

Component drift. Most notably the selenium stack on the conv board if it's still original.

Yes the selenium is still in this set was going to change it but decided since the convergence was good I left it.

Dittos to Mr. Coot.
Diodes or cold joints on the conv board. I saw a few 14 & 16" Zeniths where
the blue IIRC would pop in & out, it was the conv yoke itself. The diode pkg
can be changed with a direct sub ( ETG etc.) , OEM or separate diodes.

73 Zeno:smoke:
LFOD !

The struggle for perfect convergence on these older sets is a NeverEnding Story.
No matter how perfect you get it, it will always S L O W L Y drift off over time due to several factors, first and foremost being the selenium rectifier pack mentioned, and/or slow changes in the resistors in the circuit wich are always under load, and not to mention repeated heating and cooling cycles of the convergence clover & magnets themselves.
Even the Earth's Les Chants Magnétiques ( magnetic fields) can have an effect to some degree as it changes.
But all in all, any shifts in convergence should be rather slow and subtle, perhaps needing a slight touch up every 2 years or so with light weekly use to keep the set at peak performance.

Yes that makes sense the convergence on my set is out very small in the extreme right side only on some scenes can bearly see it. I’m not even worried about it but yes magnetics is what the convergence works on.

Small changes in sweep scan probably effect it too, changes in line voltage and tube aging will effect the amplitude and linearity of the input waveforms which should change the output some.

My line voltage has big swings here 119-123 vac

A voltage regulating isolation transformer will fix that. I've got the same problem only worse as the industrial park near me will cause voltage to fluctuate rapidly causing blooming. Those transformers fixed that. I try to run my valuable early color sets on those transformers to protect them.

Don't forget the shadow mask also plays a factor.

This is true, but not so much due to the input waveforms affecting the output waveforms (which are heavily filtered to get the parabolas), but the fact that the distortions in the input waveforms are higher frequencies that do not carry through to the output. Thus, the spot is in the wrong position for the amount of convergence current when the linearity is bad.

? I didn't think the mask affects convergence, only purity. ?

It affects both. Minor warpage or magnetism will affect purity, severe warpage affects convergence and purity, but these tubes were very stout physically and it would take a significant impact to warp the shadow mask bad enough to affect convergence.

Later tubes were more prone from bumping, and just looking at a Trinitron crosseyed would give them fits.

John

And it's been over a year and a half, and i can tell it is time to touch up the convergence again on my CTC-16XL, ans it has drifted slightly and is not as sharp as i want it to be.

I guess every times it's tuned on/off (thermal cycle ) it drifts a tiny bit. :tears:

gonna wait for the next work holiday to do it however.

as always for me it's a hours long event going round and round with my face 2 inches from the screen, cause i can't use my glasses to do it cause of the chromatic aberration the lenses cause :(

Has the convergence diode pack ever been replaced?