Found a Zenith

[Electronic M]

I'll check my parts stash.

One thing to be aware of with coils like this is that they used wax coatings on everything electronic imaginable over the years. If any of that coating was in or managed to get in to the slug/form then it will cement the slug in place unless heated or dissolved by chemicals that may not be safe for the coil... So when a slug sticks, don't force it, HEAT it.

[Penthode]

Originally Posted by Electronic M

I'll check my parts stash.

Thanks.

Originally Posted by Electronic M

... So when a slug sticks, don't force it, HEAT it.

Good advice. I have broken my share of slugs until I learned to heat them. A heat gun has proved useful for this.

[Tubejunke]

This is so odd as I was recently told exactly the opposite with the same problem, but with one of the larger coils wound on a plastic spool as found on a convergence board. Mine is a horizontal efficiency coil in my 64 Zenith. His idea is that the heat will expand the plastic and only further bind the slug. He said to use a drill bit 1/16" smaller than the bore and drill out the slug.

I guess either approach could work if done with great care as either way these things can and will turn to powder in your hands. Mine being an N.O.S. Thordarson replacement has fresh plastic which I don't want to melt of course. I was thinking more of a hair dryer than a heat gun. I was thinking a little heat and a grab with an EZ out might do the trick. The heat only being there to liquify whatever wax or resin that has ran through the slug tap.

One thing I do know is I definitely don't want to attempt finding another coil. Talk about something nobody has N.O.S. and so far no fellow collectors want to give up. Guess I can't blame them, but I never saw a post with issues there until I had mine go bad.

[Penthode]

I can appreciate not heating a plastic coil former as it will melt, deform and bind the slug. The coil former I was referring to is the brown phenolic type.

In this Zenith, the convergence coils were of the plastic variety and each had gone brittle and deformed. I called Moyers and they provided me the first two replacements wound on a phenolic core. The third (on the far right) I rewound on a Zenith plastic coil former.

[Electronic M]

Originally Posted by Penthode

Thanks.



Good advice. I have broken my share of slugs until I learned to heat them. A heat gun has proved useful for this.

I don't have any forms that long that are also threaded inside...Unless they are in something not scrapped yet. In which case it's not worth the effort to search. Sorry.

[Penthode]

Originally Posted by Electronic M

I don't have any forms that long that are also threaded inside...Unless they are in something not scrapped yet. In which case it's not worth the effort to search. Sorry.

The problem was finding a coiler form long enough.

I found a few coils I bought from Gateway in St. Louis some years ago. They were slightly too short. So I spliced the tubes together with a reinforcement. Fortunately the splice won't interfere with the windings.

I have shut down for the Thanksgiving weekend. Thanks for looking. I will rewind the transformer early next week and see how it performs.

[old_coot88]

This might be an ideal application of the 'aspirin trick'. A super handy technique for stripping fine wire without damaging it. Scroll down to posts# 26 - 28.
http://videokarma.org/showthread.php?t=257295&page=2

[Findm-Keepm]

Originally Posted by Penthode

The photo below is the set tuned to MeTV (Rockford Files) this afternoon with only a most cursory purity set up and convergence. Shortly after the set lost color lock. I decided to do the color APC and quadrature injection adjustment when the quad injection coil crumbled in the can!

I took the transformer apart and the coil former was in bits. So my call out Videokarmaland is do any of you have a spare injection coil/transformer? (It is Zenith part S-66788 and it looks like it was used in most if not all early Zenith color sets from 1962 to 1967. Note it is mounted in a standard aluminum can and has 8 terminals).

Failing finding a transformer, a two inch length of coil former which takes threaded ferrite slugs would do. I am prepared to rewind the transformer but even the formers are hard to find these days.

Any help would be sincerely appreciated.

Terry

Recheck your part number - I have a NOS S-66788 (Zenith 20S-66788, helps to know the prefixes for Zenith lettered parts!) My S-66788 is a sound quad coil, and looks nothing like yours pictured.

Your transformer may be an S- numbered transformer, or a 95-XXXX number.

[Penthode]

Originally Posted by Findm-Keepm

Recheck your part number - I have a NOS S-66788 (Zenith 20S-66788, helps to know the prefixes for Zenith lettered parts!) My S-66788 is a sound quad coil, and looks nothing like yours pictured.

Your transformer may be an S- numbered transformer, or a 95-XXXX number.

Thanks! There is a 95- XXXX number on the can. I tried to find the correct number from the parts list.

That makes sense. I'll reference the 95-XXXX number in future. I appreciate your input.

[Alastair E]

Sometimes, if a core is stuck and it looks like it'll break before shifting but the coil is otherwise good--try this--

Take another slug and screw this down/or upwards into the former--If a setting is found that then works--then great!

IF however--as always seems to be, the adjustment needs to go The Other way, remove the test-slug you tried and then use a Brass screw of same/similar thread, cut down to 'slug' size, with a slot cut into one end.
--I think Aluminium works as well for this--Could roll up some ally foil and try it...

The Brass slug will reduce the inductance as its screwed in up to the stuck slug and could well be enough to get that (whatever) inductance within tolerance for the circuit to operate normally--After all, Thats all we really need to do....
--All depends on your coil-former not being completely out of shape or too brittle, although some epoxy could help strengthen it up....

Just one of those mad things a very old engineer told me years ago, and Ive used it once on an old tube radio IF transformer....

[Penthode]

I finally got around to rewinding the quadrature injection transformer (T20) on the Zenith. Recall it suffered from heat and crumbled when I attempted to adjust it.

I found an appropriate coil form from an old unused RCA AM/FM radio IF transformer. I had to make two attempts at rewinding because of a misassumption the first time I tried which resulted in initial failure. I could only achieve proper quadrature demodulation with the demodulation axis rotated 90 degrees! I could get a decent picture with relatively good color if I swapped the B-Y for R-Y, G-Y for B-Y and R-Y for G-Y and touch up the quadrature injection. The only difference from the original Zenith transformer and mine was the input coupling winding (pins 2 and 7 on the transformer). I simply bunch wound the winding.

The original winding was a "honeycomb" mesh winding. I reckoned there was too much distributed capacity in my bunch winding. The bunch winding I believe was bringing the primary winding towards resonance: this would add the 90 degrees shift. Fortunately the AM winding from the IF transformer I dissected had two similar honeycomb windings. I used one to determine the total number of turns at 110 per winding and the second I removed the difference to provide the 37 turns I required. I assembled the transformer so that it appeared almost identical from the original.

With my second transformer reinstalled, I was able to get the correct quadrature alignment and demodulation phase with no problem.

The color lock was poor after completing the color oscillator adjustment. Probing with the scope, The burst amplitude low due to the a bad 6JC6 burst amplifier. I found the color oscillator would intermittently lock in phase 180 degrees out! I could find nothing amiss and decided to change the 6KT8 oscillator/reactance control tube for the heck of it. Color lock was now excellent. (I decided to replace all the 6KT8s in the set because I do not trust the critters).

I really like the picture on this set: it is crisper than my RCA's and I really like the Zenith picture. I did not bother with Video IF/ Sound IF or chroma channel alignment because the picture and sound are good. The picture indeed looks better than the photos. The set is using the original Zenith CRT.

The CRT looks to have had a hard life but appears to have a lot of life remaining. Sure glad it wasn't necked!

[DaveWM]

looks great, excellent convergence as well. That set sure has come a long way, great work!!

[Findm-Keepm]

PLEASE take your right hand, reach behind your left shoulder, and pat yourself on the back! Well done - another Zenith beauty!

Congratulations on the engineering and persistance!

Cheers,

[Kevin Kuehn]

That picture really looks wonderful.

[Electronic M]

Nice work!