Very interesting zenith observation
 

I was working on one of my portable zenith color sets today, a 15Y6C15 14" set from 68. I wanted to touch up the focus, as I couldnt get it quite right. Since I had the set apart, I wanted to check the cathode current as I never did on this set. I looked at the schematic and noticed there is an efficiancy coil in this chassis. I was confused as I couldnt find the coil ANYWHERE! Ive got another 15Y6C15 set (earlier model) and pulled the bottom off, right away I noticed the coil beneth the chassis.
Ive got a full line up of zenith service data, and noticed that even the late production 15Y6C15 sets used an efficancy coil. I compared both sets circuits and I am lead to believe that zenith FORGOT to put the efficiancy coil in! The solder joints all look factory from the points of where the coil would have been soldered in, and I couldnt see cut wires. There was also a missing .01/1000volt capacitor, 7W 100 ohm resistor as well? Get this, the cathode current runs at 140ma in this condition! Couldnt find any info on this chassis, its simply a 15YC615, with no suffix. (suffix would indicate a modification) I know andy(?) has this exact same set that he restored. Im interested to find out if you set has an efficiancy coil. (its underneath the chassis, but not on the rear apron, its mounted tward the front, or infront of the HV cage)
Perhaps this was a zenith prototype that never made it to production this way? I have run into zenith employees who have had non production zenith equipment. Or Maybe this set was built on a friday :D I got this set from on older man down the road who had many old sets in his basement. He told me he had this set for 20+ years and couldnt remember who gave it too him. Hes the same man I got my space command 400 roundie from which he bought new.

I guess it is understandable that the set could work properly without the efficiency coil...after all, later model black and white sets don't use one (though some of the '50's sets do). You would just not have any control to compensate for tube or component aging. I don't think the Portacolor uses an efficiency coil either.

That was one way to get the HV working in a TV in which the efficiency coil was shorted (or if the coil core, which was iron and often grounded, shorted to the winding)--simply remove the coil from the circuit. The set would now operate normally although, as another poster noted, it would no longer be possible to make adjustments to allow for weak tubes and/or components. Note, however, that if the core of the efficiency coil shorts to the winding, the coil will smoke and the HV will be lost immediately.

I know mine has an efficiency coil because I remember adjusting it when I first got the set going. There was at least one revision to this chassis. The later revision had a flyback that was potted in silicone and there was a varistor in the the HV regulator circuit. The early one uses a different potting material and has a silicon diode in the regulator near the HV control. I can't remember if it eliminated the need for the efficiency coil, but it may have if the flyback was able to handle higher temps.

I just checked my book on 60's Zenith TVs and it does say that some chassis with the silicone flyback don't have an efficiency coil. Apparently, the silicone transformer isn't as lossy as the polyester transformer, so it produces less heat. Your set is probably as it should be.

Hi andy,

thanks for looking into that. Im glad to know my set is original!

I'm curious who made the CRT in your Zenith. Mine has a Zenith branded tube, but it has an RCA EIA code (275, I think). I guess mine was made before they were making their own 15" CRTs. The Zenith logo on the lable is printed in the typical RCA red ink.