Quote:
Originally Posted by madlabs
And IIRC centering is with the magnets in the yoke?
How do I determine proper overscan?
What is neck shadow? And does the yoke position affect the focus at all? Or anything else?
So, crank up the signal from my BT modulator, then back it off? What is tearing?
Thanks folks!
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Centering magnets are on the back of the yoke. They are the rings that the neck passes through they have two ears to grab and rotate. The centering rings affect both horizontal and vertical centering simultaneously.
There is no hard and fast standard for overscan. If total horizontal overscan is under 1/3 of total scan width and the screen is filled then it is within normal range....Overscan varies heavily with utility voltage, health of the tubes, etc....That is why it is best to not to aim for any specific spot on the dart board but just be sure to hit the board somewhere. Horizontal overscan is usually the hardest to control, so whatever the horizontal is, best live with it and adjust the vertical to match....so round things (like clocks) look round and not oval.
Some of my tube color sets that I do serious watching on I actually adjust the underscan by using a variac to change the AC power input voltage.
Neck shadow is more commonly seen in early post-war sets....Basically, it manifests its self as curved unchanging dark patch near the edge of the screen.
AGC is not a knob on your modulator, but rather it is a knob on most TVs...IIRC most predictas were too cheap to have an actual AGC pot and instead had the Local-Distant range switch normally reserved for loss leader portable sets....Which brings up another point:
These predictas have very cheap crude circuit designs, they are not tube broadcast monitors, Dumonts or even Zeniths....Sweep is not going to be as precise or adjustable as even the middle of the road brands of the day letalone the solid state CRT sets we often subconsciously use as yardsticks to compare all CRT sets against. Perfection is a waste to pursue as it will constantly drift away from it even if achieved.
As long as round objects are round, a cross hatch grid is fairly reasonably even spaced in both axes, the center of the image is within 1.5" of the CRT center, and not more than 1/3 overscan or any underscan then your set would probably be in the top 60% of performers if you went back in time and compared it to other predictas when they were new...And you will not notice problems watching natural sceenes and period material....Some modern material letterboxing, sports and news graphics, DVD menus, etc mimic test patterns and show off the design limitations of such TVs.....It is sort of like feeding a HiFi test/demonstration recording into a 30's table radio or a 60's transistor radio; The limits of the circuits are made (somewhat painfully) obvious.