Zenith 28T962 "Warwick" restoration
 

Another day, another porthole. This is my only purchase from the early TV convention last weekend. Not from the auction or swap meet though. We struck a deal weeks before. It was just a convenient destination to make the transaction.

I just couldn't resist because of the condition. One of the nicest late 40s sets I've yet encountered. The original finish is in great shape, all the hardware and back are present. No corrosion.
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You can see the original color behind the control doors where it was protected from UV damage.
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Super clean power supply.
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The chassis is essentially the same as the "Stratosphere" and "Waldorf" sets I've worked on recently. Just a different cabinet style and CRT. An aluminized 12KP4 this time around and it's good!
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I only see one repair. A power resistor has been replaced.
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Most of the tubes I can see so far are Zenith branded.
The only concerning thing so far is the HV cage is missing and flyback has been replaced. With a genuine Zenith replacement part though.
The coating has seen better days and looks like a good candidate for "the treatment". Soak in spirits to dissolve the gunk and recoat in poly in other words.
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Honestly, I'm a little tired of working on them, but I figure I should while it's fresh in my mind. I'll do the usual replacement of all the bumblebee paper caps, corroded sand coated power resistors and bad electrolytics.

Finish is super nice behind the knobs as well, usually worn down to the bare wood.

That may be the last year they buried caps inside of the IF cans. Those are the ones that suffer from the infamous silver disease, if I remember correctly.

Work on the chassis has commenced. No surprises so far.
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The excellent service manual with detailed block diagrams and theory of operation can be downloaded free here: https://www.earlytelevision.org/pdf/...25r_manual.pdf

Meanwhile, the cabinet got the usual treatment. Cleaned with pumice free mechanics hand cleaner, then Howard's restore-a-finish, followed by wax.
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I replaced all the open power resistors and rebuilt the horizontal and vertical oscillators.
Then decided to do a power up in stages.
All filaments lit with no rectifers.
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Popped the 5U4s back in a went for it again. Yes, we healthy HV (EHT).
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After some control manipulation, I was treated to a raster with bad ringing. Time to replace more leaky caps.
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I've moved on to testing the tubes. Most of them do appear to be the original tubes and many are very, very weak.
The two 6CA7s, a 6V6 and 6K6 are especially bad. Someone really drove this set into the ground.
It will take a little while to dig up replacements for all of them. I'm curious to see what difference it makes.
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I must admit I made a mistake testing some of those octal tubes. They are weak but not quite as dead as I showed earlier.
I ended up replacing 8 tubes so far and it made a difference.
Noticed right away that the image was brighter. Still some ringing though.
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Fed in a test pattern and was able to get a lock easily.
Bit of distortion in the upper-left and a shadow around the bottom. I think the focus coil has shifted out of position.
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There is some odd interference in the image if you look close. I don't think it's just chroma dots.
Like watching through a screen window.
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I touched up the video IF alignment with a vintage HP 8568B spectrum analyzer + tracking generator. It took some experimenting to get it setup properly but the final results are great.


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The color info is coming through as dots indicating a wide bandwidth.
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:thmbsp:

Here's the multi-burst test pattern. I have definition all the way out to 4.5MHz on the far right.
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It's a little odd tweaking the egg-shaped linearity
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Had to laugh, Bob. One of your pictures looks like one of those irritating "Plexaderm" commercials.

But seriously, looks great.

That's a nice use of a spectrum analyzer. Since the spectrum analyzer wants an RF signal, not a detected (amplitude demodulated) signal, do you grab the signal right before the video detector? And insert at the tuner mixer tube?

Yes, I have the probe at the input of the detector. I injected as indicated in the alignment instructs at the grid of the 3rd, 2nd and first IF tubes.

Here's the overall video IF response curve using an HP 8662A sweep generator injected into the mixer tube. Pretty darn close the service manual I think.
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