Zenith 28T960 porthole restoration
 

I recent picked up this 12" blonde Zenith porthole at an estate sale. I may go back for the other if it's still there. Had to save room in my car for a CTC-5

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The chassis inside are in excellent condition. Mostly Zenith branded tubes and no signs of any servicing. 12LP4 Picture tube tests good.

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That's what I love to see :D
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A few cosmetic issues unfortunately. The biggest being the hinged control doors are missing :tears" Anyone have a spare set?

Also, the top appears to have been clear coated with something that has cracked and crazed. The sheen and feel is different than the rest of the cabinet. Reminds me of the acrylic finish on German consoles from the 60s.

Also looks like the original speaker is gone? It is branded Zenith, but small and mounting holes don't line up.
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This is what those missing control doors look like.
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https://www.youtube.com/watch?v=GuAXcZmLNmM

:drool: :sigh:

I Can't find stuff like that down here. :(

I was rather surprised to discover the crazed finish on top was shellac! Even better the crud I thought was damaged was all junk on top of the shellac!
Denatured alcohol and a little scraping got it off. I ran out of alcohol so it's not quite done, but here's how it looks so far.
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If I need to even out the color, I may use a little tinted lacquer or stain. Then clear coat with lacquer.
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Got the main chassis up on the workbench for some preliminary work.
Cleaning, tube checking and replacing the obviously bad parts.
That would be all the open power resistors and burst capacitors.
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Brand loyalty or maybe an extended service contract?
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The original tubes are dated 9-48
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Every single power resistor is corroded and open.
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I've been struggling a bit to identify exactly what model I have. It doesn't help that there is no tube chart inside and no indication there ever was one!

My main chassis is a 27F20 which has scant service info.
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I found this in Riders vol 3.
Obviously, this is a blonde cabinet which should make it a 28T960 "Waldorf" but that should be a 28F20 chassis.
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What a beauty! That is one huge transformer. Is that big rounded part all the tuner?

I wish I was in an area where there was even a slim chance of running into sets like these.

From what I found in the PF reporter and photofact index it tracks to 27T965R. Same as your results. Nothing on the blonde Waldorf with that chassis number. There's quite a bit of info on broadmoor on radiomuseum.org

Could be an undocumented cabinet option or if the 2 chassis have compatible bezels an aftermarket cabinet swap.
I've got a 1963 Zenith color roundy that someone stuck a 1965 Zenith roundy chassis in decades ago... don't underestimate what someone with a dead set with a good cabinet, another working set in a ruined cabinet, some time and some beer could do 50 years ago.

Yes, that's all the tuner :D

Sure, anything is possible, although it seems original. Very little signs of servicing and all the bolts were present. What really gets me is the lack of any labels or tube chart.

I started working on the power supply last night.
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I removed the two caps on insulated wafers. One had vented and the other has excessive leakage.
A little help from a heat gun got the old cardboard covers off. They are Zenith branded and I'll reuse them to hide the new caps.

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Naval Jelly took care of the rust.
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New caps installed.
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Test fitting of the old covers. I'll clean them up a bit before securing them.
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I was able to reform the one original dual section cap remaining.
That wraps up work on the power supply.
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I've also started patching up the cabinet. I will attempt to paint the filler to match the original finish.
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That power supply looks like it's the same one used in a table-top set. The giveaway is the shield around the transformer, and the flange at the bottom. The power supply slid nicely into slots on the side of the cabinet. Either the PS was replaced, or Zenith depleting stock? I had the same model years back, very pristine set.

Did you ever go back to get the "Aldrich"? After moving, that is the only set I have left. Packed it carefully 6 years ago, still in the same box. VERY minty set, with NOS Lazy Bones remote control.

but of course plus a Muntz :D
Very good condition with owner's manual. Rebuilt 16GP4 is good.
I'll start a separate thread on it.


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Wow, very nice! I see circular marks at the corners. Maybe the Zenith had a glass top one time?

Probably. There's a felt pad in each corner.
Time for a power up attempt.
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OK, nothing. B+ is close to spec, but no HV and no sound.
Started by replacing a few caps on the horizontal oscillator. One had split open and one looked like a mica cap, but it's leaky paper inside.
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That got the oscillator running and we have HV :)
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Vertical is crunch though so went after that next.
Replaced a couple caps on the vertical output and that helped a lot.
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Injected a signal next but cannot lock horizontal. Just not enough range on the freq or phase controls.
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Replaced a couple caps on the 6AC7 AFC reactance tube.
All of these are paper caps and all are bad.
The one on the left was actually getting warm. Replacing that got a lock!
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Not bad for just replacing a few caps and open power resistors.
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Gettin' there!

I replaced the coupling cap from the volume control to output amp. That got the sound going.

Waiting on parts from Canada to continue.

Meanwhile, here's a comparison of "normal" versus "zoom" mode. Bad compression on the right side.
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the picture looks a bit M*A*S*H ed! :D

For as few parts as you've changed the picture looks quite sharp.

I decided to give these JFX premium polypropylene caps a try. I got them from Just Radios.
I figured black was a nice change from yellow ;) Long leads and easy to work with.
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Also, if one was so inclined, they do fit nicely inside a cracked open bumblebee.
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Replacing a couple caps on the horizontal output tube helped the smooshed right side.
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That's looking better!

Bob after seeing all these nice looking restuffed caps you've done, you're getting me more inspired to start restuffing caps. I did restuff the electrolytics in a Marconi portable tv radio combo (Emerson 1232) and they turned out nice. They were the paper can multicaps with the shellac end like you'd find in an AA5 radio. I wished I had axial lead caps on hand when I replaced the wax paper caps. I may revisit it in the future and swap them out with the restuffed originals.

Still having both vertical and horizontal linearity issues, but the image is looking pretty good.
There are three multi-section electrolytics on the main chassis I haven't touched yet. That includes the vertical output cathode bypass cap. I expect replacing those will help.
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While certainly not necessary, restuffing these old bumblebees is fairly easy and I think looks nice.
I'm just leaving the black caps as is when replacing the grey ones.
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Just about done :)
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I'm impressed you can reliably split them like that. I've found that unless the paper inside swells and they split themselves in half cleanly, they usually shatter into a mess of jagged bits when I try to split them.
How are you splitting them?

Here's a short video showing the process. I've gotten better since I made this.
Fresh utility knife blade placed right along the seam plus a few taps from s small hammer.
Flip it over and do the same on the opposite side.

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Finally getting back to this set hot off the heels of a 28T962 with nearly identical chassis. https://www.videokarma.org/showthread.php?t=277669

Wrapped up the recap and breezed through the alignment since it was fresh on my mind.
This set has a 12LP4A rather than the aluminized 12KP4 in the 28T962. Even so, the image quality is comparable.
It certainly has great bandwidth with very visible chroma dots.

Now, if I could just find a set of chrome control doors...
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