Rare Automatic TV-707 Rescue!

Sorry I’ve been away- this time of year is always jam packed with jobs needing to get done before Christmas. The good news is, after December 25th I should have a great deal of time to get back on some of the in-depth and long-term restorations.

You might remember the estate of a TV collector I acquired earlier this year (if not, check out the Vintage TV Hoard post.) I managed to acquire a couple dozen or more 40s and early 50s era TV sets; mostly 7″ electrostatic sets and most of those being more pedestrian models.

automatic TV-707 restorationautomatic TV-707 restoration

Thanks to my friend and fellow collector Roy C., whose knowledge of electrostatic TVs far surpasses my own, I learned that this 1948 Automatic was one of the rarer sets in the entire bunch. Sadly, though complete, the cabinet had sustained heavy water damage. Normally in a circumstance like this and given a more common TV I would consider a part-out… but with this one it was decided to be worth restoring.

automatic tv-707 restoration automatic tv-707 restoration

IMG_1500automatic tv-707 restoration

Check out the condition of the chassis… very complete! Someone replaced the 6000 volt rated tubular deflection capacitors with 3000 volt ceramic disc caps wired in series… generally a no-no. Why? Because even given that we have a substitute capacitor of the same value and voltage rating (two 3000 volt caps wired together in series to achieve a 6000 volt rating,) other factors such as a difference of impedance between ceramic disc and tubular caps causes problems when they become subjected to different frequencies. Ceramic disc capacitors also generally have a positive temperature coefficient which means it varies in value as the component’s temperature changes.

IMG_1500automatic tv-707 restoration
Pesky ceramic disc caps!

Case in point: ceramic disc  caps are “OK” in the horizontal deflection section when operating at the 15.75khz scan rate… but when placed in the vertical deflection section (a comparatively low 60hz scan rate, compared to 15.75khz or 15,750hz) ceramics can cause there to be many undesired effects upon the picture such as non-linearity, vertical compression, and line pairing. What does this mean? Impedance of the ceramic capacitor causes it to be ‘seen’ as a different load based on the frequency it is passing. 15.75khz… no problem! 60 hz…. load’s now out of spec, and if I could write any more about the subject it would be a sad, sad tale. Moral here is: just don’t use them!

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Fortunately, they were ‘good enough’ to grace us with the presence of a bright raster when I brought the power up on the variac. Great news! These caps are usually some of the first to fail, and are often the ones which prevent an electrostatic TV from displaying anything on the screen.

All good and well, but let’s now step into present-day.

Today I received the cabinet back from Lance at Nook & Cranny Refinishing. I’m absolutely blown away at what he was able to do with the cabinet! He completely rebuilt the decrepit side and refinished the entire thing. It’s absolutely gorgeous.IMG_2114[1]IMG_2113[1]

Well that’s about it for now, back to the grind. This TV is one of my own pet projects and naturally gets relegated to the back burner….. but SOON. 🙂

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