Recognize this set?

[ctc17]

What dave said on the tuner, but I usually slide the cracked gear off, clean it up really good and jb weld it back on the ribbed shaft. Every zenith I own has that gear cracked.

How was the cutoff on that crt? Were you able to get up to high in the red? What kind of emission do you get at 5 volts? (i have the same crt tester)
That red and green color bleeding can be caused by a semi week crt.

[JCFitz]

Originally Posted by ctc17

What dave said on the tuner, but I usually slide the cracked gear off, clean it up really good and jb weld it back on the ribbed shaft. Every zenith I own has that gear cracked.

How was the cutoff on that crt? Were you able to get up to high in the red? What kind of emission do you get at 5 volts? (i have the same crt tester)
That red and green color bleeding can be caused by a semi week crt.

I wonder at what age the fine tuning gear started cracking and the UHF shaft swelled up? I sold my 20Y1C38 in the early 90s and no problems with the tuning mechanism. Worked great.

[IsthmusTV]

Thanks everyone for the guidance. You guys are spot on about the tuner. I'll disassemble it and do it right. As for the CRT, I'm afraid it is on the weak side. I couldn't get the red channel up to the "gun bal" line on the meter so I don't know how valid the emissions test is. The green and blue guns seem OK. I didn't test the CRT specifically at 5 volts, but emissions dropped pretty rapidly on the life test. So, I'm not sure how much effort I want to put into this set if the CRT tired. On the other hand, it is making a very watchable picture that seems to be getting better all the time. I do have an old Heathkit C-3 cap checker that I can use.

I may not have much time to work on this set for a few weeks, but I'll post my progress when I do.

Thanks again for the help,

Clark

[julianburke]

I have worked on hundreds of this model since they were new. The AFC control does work and make sure it is "OFF" when you are fine tuning it. It will be difficult to fine tune if it is on. It was more of a selling point and fun to demonstrate when it was in the showroom. If it does not fine tune, the little gear that engages the strips in the tuner is split and needs to be replaced which was a common fault in these sets. I may have a NOS one.

[old_coot88]

Originally Posted by julianburke

...If it does not fine tune, the little gear that engages the strips in the tuner is split and needs to be replaced which was a common fault in these sets.

Yes, that was true even when the sets were just a few years old. We always just epoxied the split gear back on, after first cleaning it and the shaft thoroughly. Worked fine and never had a call back for that problem. Bill(oc)

[IsthmusTV]

After being busy with other things, I'm now preparing to replace all the electrolytics in the PS. The cans are rated at 475 Volts. Would it be OK to use caps rated at 450 Volts? It seems that you really pay a premium for electrolytic caps rated at higher voltages. For my Emerson 637 which also had EC's rated at 475 V, I used 500 V caps from Antique Electronic Supply. I later read on ARF that 450 Volt caps would have been fine. Any thoughts?

Thanks,

Clark

[ctc17]

Is there a reason to change the caps? Is there a problems or is it just about the popularity of recapicide? I have several of those sets and the cans are good in all of them.
You need to use the 500 volt ones if you have to change em.

Most likely you will create more problems than you will fix, if it works leave it alone!

[IsthmusTV]

Hi ctc17,

Thanks for the reply. That's what I was wondering, too. I hate to do a recap if it's not necessary. The cans don't get warm but there are some issues with the picture that might be caused by the power supply: Both the height and width are inadequate (even after tube substitutions) and there is a ripple in the picture that drifts slowly upward. Also, there is a really annoying hue shift that coincides with this ripple. I have subbed most tubes, but not all, so it could still be a tube issue or a leaky cap elsewhere.

Also, I suspect that the 6HS6 HV regulator may be weak, even though it tests OK (I don't have a sub for it). If I turn the brightness up too high, the picture dims and begins to fade away. I have tried two different HV rectifiers. I haven't attempted to measure and set the HV yet, though. I know that this set has HV regulator issues but I haven't heard what that translates to in terms of performance problems.

-Clark

[ctc17]

Originally Posted by IsthmusTV

Hi ctc17,

Thanks for the reply. That's what I was wondering, too. I hate to do a recap if it's not necessary. The cans don't get warm but there are some issues with the picture that might be caused by the power supply: Both the height and width are inadequate (even after tube substitutions) and there is a ripple in the picture that drifts slowly upward. Also, there is a really annoying hue shift that coincides with this ripple. I have subbed most tubes, but not all, so it could still be a tube issue or a leaky cap elsewhere.

Also, I suspect that the 6HS6 HV regulator may be weak, even though it tests OK (I don't have a sub for it). If I turn the brightness up too high, the picture dims and begins to fade away. I have tried two different HV rectifiers. I haven't attempted to measure and set the HV yet, though. I know that this set has HV regulator issues but I haven't heard what that translates to in terms of performance problems.

-Clark

Ok, for some reason I thought you said it had a perfect picture. Thats sounds like a reduced value power supply capacitor. You can test them and change the bad ones or replace them all.
They reason they are rated so high voltage is because the voltage is real high before the tubes warm up and load it down. Ill look at the schematic when I get home.

I would replace all the white tube type caps while you have the chassis out.

[ctc17]

I bet C1A and or C2A is open.
If it was my set I would jump a 100uf at 450 volt axial accross the bottom. You can test them easily with an esr meter or speaker and audio source.

[miniman82]

Insufficient vert height can be caused by low boost voltage, drifted resistors in the height circuit, and a bad height pot. What's HV measure?

[IsthmusTV]

I ended up ordering all the electrolytic caps as part of a larger cap order I was placing anyway. I know that I'll use these caps for something if the cans in the Zenith turn out to be OK. But I think I may try your suggestion of jumping C1A and C2A temporarily with 450V caps just to see what happens. I also ordered a bunch of tubes, including a new HV regulator and an HOT.

And miniman82, thanks for the leads on the insufficient vertical. I have yet to measure the HV. I plan to do that this weekend.

-Clark

[DaveWM]

the white elmenco HV caps (1kv IIRC) should be replaced I think there are two, one up by the damper the other near the front of the chassis, part of the vert, if the vert is a bit jumpy esp. HV regulation with the 6HS5 is not as good as the older 6Bk4, I can see where they made quite a few changes in that circuit over the models. I understand it is better as far as no X ray radiation (loads down the FLY at much lower voltages), but I will take the 6bk4 shunt tube over it every time.

Be very carefull handling the chassis, all those point to point parts can be easy to move with the uncovered bottom, and likely to short something out, I had this happen on some of the larger disk caps, they have relatively thin leads and it does not take much effort to move them around.

[IsthmusTV]

I finally measured the HV and it's a measly 16-19 KV. The HV adjust seems to have no effect. Would that likely be the shunt regulator? I swapped out the HV rectifier with no change. Of course, the tube that is out of stock on my order to vacuumtubes.net is the 6HS6 (the HV regulator). The one I have tests OK but as we all know tube testers can be very wrong. Clearly, all is not well with the HV on this set.

Also, I re-tested the CRT and now emissions from the red gun are even lower (in the white area between replace and good). Oh, well. I'll proceed with the PS recap when my order arrives and see where that gets me.

Thanks again for the help,

Clark

[ctc17]

Check it with the regulator tube out, i dont think this chassis has the safety to protect against that. If it goes up look for bad resistors. Its not a HV shunt, it regulates the HV by clamping the 900volt boost. There is no danger of running the set with it out.

I had one of these that had a bad resistor and was causing the regulator tube to clamp super hard. It melted the regulator tube.

It could also be due to low b+ from bad caps.