Quote:
Originally Posted by VintagePC
IT'S ALIVE!
A couple of things need doing though... and I'm not sure where to begin on some of these... Any advice?
1. B+ seems a little high. Schematic calls for 260V, I'm getting around 310 with the variac at 95%.
3. On switch-off, vertical and horizontal collapse as is expected... but there is a REALLY bright spot left over gradually expands and fades away over about 30 seconds or so... this seems far brighter and more concentrated than seems healthy, and something I do want to resolve asap before I run the set too much more for testing.
4. Vertical height is about 75% of the screen space with the control at maximum. Probably something to do with the bodge job on that control. Again, something I need to investigate after #3 is done.
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Congrats! Looks like you did a good job.
1.) Adjust the voltage from the variac to what the schematic specifies as the line voltage present when the authors of it took their chassis voltage measurements if the B+ is within approximately + or - 20%(I probably would not worry if it were within 30%) of the listed B+ you should be fine. The grid in many rural parts of the USA(and I'd guess Canada too) were not designed for loads such as many large kitchen and home appliances, and at different times a day the grid(and thus the B+ which varies in direct relation with the power grid) could be below 100V or well above the 117 that was the common standard then....TV makers were aware of this and made sets which could tolerate a fairly wide range of power grid voltage. If your set's B+ runs more than 30% high when plugged directly into a wall outlet then I'd do something to lower the voltage coming in. A few things you can do to lower the power grid voltage reaching it(that don't involve tying up your variac constantly) are to use a 100'+ long extension cord(it's resistance will lower the voltage some) or get a 120V to 2-20V stepdown transformer and wire it up as a line bucking transformer(there are threads on this if you search).
3.) This could be normal for this model... You may be able to dim of suppress the spot by adjusting brightness or contrast after shutoff. I have sets that do this which are fine, but there is one where there is a small black dot in the center of the screen where this effect burned the phosphor clean off at some date prior to my ownership of it. There are threads and IIRC even vintage electronic magazine articles on how to modify sets to not produce the spot.
4.) Look for out of tolerance resistors, wiring mistakes, and test the tubes. Some sets(Muntz was infamous for the degree to which this applied to them) will sort of work with tubes that test in the lower end of good, but only work well with a VERY strong example of a given tube type. You may need a tester and a source of several samples of the given vertical tubes, from which to choose the strongest, in order to get enough oomph to get the vertical to fill. Running the set with high B+ should also help with shrunken vertical.
EDIT: BTW the program you have on looks to be a letter boxed program(google that if you don't know that term in this context) letter boxed programs naturally don't fill the screen vertically so when adjusting the screen use a native 4:3 aspect ratio test pattern or program. Despite the program being letter boxed I can still tell the vertical is too small because the two horizontal Closed Captioning dashes well above the rest of the image, which should be JUST above the the top of the viewable area of the CRT, can be seen on screen.
Good luck!