1963 Zenith 29JC20 restoration

[Zenith6S321]

Originally Posted by old_coot88

My very first concern with that set would be the integrity of the plastic/(nylon?) coil form of the H efficiency coil, which tends to crystalize over time and fall apart. If that happens, the requisite 'dip' in cathode current of the H output tube is lost, allowing the current to soar 'waay over spec.

At the moment mine is still intact. Is there some way to visibly see that it is crystalized? On other sets where the ferrite cores have been tight, I have let them soak in a little WD40 which seemed to ease their movement. Any suggestions for this coil?

[old_coot88]

Originally Posted by Zenith6S321

At the moment mine is still intact. Is there some way to visibly see that it is crystalized? On other sets where the ferrite cores have been tight, I have let them soak in a little WD40 which seemed to ease their movement. Any suggestions for this coil?

From the photo, it looks like the coil form is phenolic. If so, you're in luck. The whitish, semi-clear plastic forms are the ones that crystalize.
If the three blue adjustment coils on the convergance board also have phenolic forms, you're doubly in luck.

[Zenith6S321]

Originally Posted by old_coot88

From the photo, it looks like the coil form is phenolic. If so, you're in luck. The whitish, semi-clear plastic forms are the ones that crystalize.
If the three blue adjustment coils on the convergance board also have phenolic forms, you're doubly in luck.

Yes the convergence board coils also look the same. From a couple of tags on the set I think it was made in 1963. Maybe Zenith changed to phenolic coil forms by then.

[Electronic M]

Originally Posted by Zenith6S321

Maybe Zenith changed to phenolic coil forms by then.

It is the other way around. The phenolic forms are the old type, and Zenith moved away from them to the notorious plastic forms that they had from the mid 60's to the late 70's.

[Zenith6S321]

I tested the coils today and I think they are all ok. There is some wax on the bottom of the HV cage but the flyback otherwise looks and tests good. I'm not sure how concerned to be about the amount of leaked wax. The flyback shows 16 rings on my Sencore LC75. The 3A3 plastic socket cup is broken but I think it might be fixable. The cloverleaf has split and looking back at the service tag it lists a 43-473 which is the part number for the cloverleaf. So this set has had two of them and I guess both broke. I wonder if separating the cloverleaf into the three sections at the place where the plastic springy area is and then using an actual metal spring between the section could work.

[Zenith6S321]

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

[Carmine]

Originally Posted by Zenith6S321

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

Out of curiosity, how many resistors were bad and by how much (worst case)?

I also have one of these sets, so I'll be watching.

I notice two holes punched in the tuner bezel... Does this have an optional UHF Tuner? If so, I've never seen them arranged side-by-side on a Zenith roundie... Usually it's diagonal.