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Old 01-09-2018, 09:09 PM
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Bob Galanter
 
Join Date: Sep 2005
Location: Whitefish Bay, Wi (Milwaukee)
Posts: 1,053
A GE 15CL100 Lives again!!!

I spent Saturday 1/6/18 with the new owner of this set. He has acquired a good 15GP22 from a kind collector who was willing to part with one of his coveted good spares. I will not mention his name but this generous collector has our eternal gratitude.

The new owner of the set has completed a complete recap of the set, including re-stuffing all the cans.

Upon initial power up the set had a raster but within a minute or two the raster disappeared.

I am sure all of you know that horrible sinking feeling when your HV goes down. The first thing we all think of is "oh no I hope the flyback has not taken a dump" and in the case of a 15CL100 this would be a catastrophic event, because there are no replacement flybacks available for this set. It used one specific to this set.

So Saturday was spent running down the reason for no HV. Although visually the flyback looked very nice, that is never any guarantee that it's good. It ohm'd out nicely so that was an encouraging sign.

Scoping the waveforms in the horizontal oscillator section was encouraging and showed that we had the correct waveform at the grid of the 6CD6 pair.

We replaced the pair of 6CD6 HOT tubes because they tested marginal and the new pair gave us more of a corona on the plate caps but still not anything to brag about.

The set uses a voltage trippler design similar to the CT100 and 21CT55 but has some odd ball rectifiers, 2V2 and a strange shunt regulator made by GE just for this set. All of these had been replaced with NOS tubes. After some considerable farting around which wasn't getting us anywhere, we decided to start disabling the rectifiers in the trippler circuit. We pulled the 2nd and 3rd stages of the trippler and VIOLA we had about 12KV, with sparks flying all around. Then we enabled the 2nd stage again and it popped up to about 18Kv. But when we enabled the 3 stage, it dragged us back down to nothing. Our conclusion was that the 2000PF 30KV doorknob was leaking. Often a bad doorknob will get rather warm (a sure sign that the DN is bad) but this one was not getting warm at all.

I just happened to have a couple replacements at home in my inventory from when I restored my CT55 (which also had a bad one of these 2000pf 30KV doorknobs.) I usually buy estras of strange parts like this to have on the shelf, because you always have to special order them. Something I learned from my dear friend John Folsom. John's motto is "it's all about the spares" A good motto to live by if you are serious about this hobby.

The replacement doorknob is metric threaded and of course the old GE parts that screw into the DN were Inch thread. So I made some mods to the old GE hardware so that the hardware could be adapted to the new metric threaded DN.

When the set was fired up we got a nice 25KV. The shunt regulator ckt is not working so we still need to address that issue.

The plastic hub on the fine tuning knob was completely broken off of the knob that came with the set. Upon digging through my extensive knob collection, I was able to find an exact replacement that needed some minor fixing. I machined a copper sleeve to place around the plastic hub of the knob and cemented it in place with JB Weld. To make sure that the JB Weld did not ooze into the hole that the shaft goes into, we coated the brass knob shaft with a thin film of silicone grease and inserted the knob onto the shaft. When the JB Weld was cured the silicone grease allowed the knob to slide off of the shaft very easily.

So, progress is being made and here are some photos showing that it is producing color at this very early stage. It still needs work but we are confident that the remaining issues can be addressed as time passes.

The last photo is the GE (on the right) next to the Stromberg Carlson K1 that came from Ed Reitan's collection, for comparison. The photos do not do justice. They look far better in person.

EDIT: Suggesting that this thread might be more appropriate if moved to Early Color Sets

Edit: Photo added
Attached Images
File Type: jpg GE2.jpg (69.9 KB, 148 views)
File Type: jpg GE1.jpg (59.4 KB, 141 views)
File Type: jpg GE3.jpg (40.2 KB, 174 views)
File Type: jpg GE and K1.jpg (56.9 KB, 94 views)
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Last edited by ohohyodafarted; 01-20-2018 at 01:22 PM.
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