Zenith 24h20 Porthole
 

I have begun work on the Zenith Porthole that I acquired for free off of Craigslist. As found, it was complete, but the cabinet had been stripped of all its finish, and the grill cloth was hacked out and replaced with some modern brown knit fabric.

The crt is a replacement, but it tests strong with a good life test. Digging deeper, I was disappointed to find the audio output transformer open. luckily, I was able to dig in, and solder some new leads to the hair thin windings of the transformer. It looks terrible, but it works perfectly now. Now to begin the recapping.....

http://s288.photobucket.com/albums/l...9.jpg&newest=1

No pic.

Let's try this again...

http://i288.photobucket.com/albums/l.../zenith009.jpg

Reminds me of when I hand re-wound the main coil in my tube radio because the mice ate it for lunch. I don't know what it is that drives us to fix it given what we have on hand, but it's pretty awesome to hack something together and have it work. Sure, we can buy new, but where's the fun in that?

(Moreso in my case, since it was my first coil wind, from scratch, by hand, using wire salvaged from a CRT yoke). Goofed up the polarity, and did something that looked like this to fix that, but hot damn, it worked without any IF alignment!)

Thank you. It really does look pitiful, doesn't it?

Off to the left, you'll see a pair of black leads-the previous owner pulled so hard on those wires that they were ripped from the transformer, separating both the primary and secondary leads as well. Other damage to the set appears to be the fact that someone tried to power this set up recently-putting on a new power cord and applying power. The lytic cans all are swollen and leaking, and a couple of the resistors associated with the power supply look toasty.

Everything is all wired in now, and it does work. Spent some time recapping, and even though this is a 2 chassis set, which usually gives you plenty of room to work, this set uses 4 multisection can capacitors, so things are going to get tight real quick...

The above post is spam-please remove-thanks.

Done

Are you restuffing the cans?
It makes a much cleaner installation if you do and it's easier to work on later without all those caps under the chassis. :yes:

What makes it look so bad is just the browned, aged paper. :) My audio output transformers looked the same, and until I tested the continuity, my main thought was "gee, I hope those are still OK".

Rewinding coils is one of those things regarded as a black art by those who don't know the secrets... (or have a machine) but once you know them, it's really not that difficult at all!

Can't really restuff these cans, as this set uses several sections that are 475v, so I had to jump up to caps that are just too physically large to do so. I'm just about done with the basic capping (new lytics and paper/bumblebees replaced) so I'm working towards the initial powerup now.

More problems with the audio amp: I found a wiring mistake that messed up the cathode bias on the output tube, causing the amp to remain silent.

After that was cleared up, I finally had a roughly recapped chassis:

http://i288.photobucket.com/albums/l.../zenith012.jpg

But more audio issues were evident: I wasn't getting any audio still, although the amp was sound. I found an IF tube was dead (open filament) but still nothing. Something wasn't quite right with my measurements on the oscillator, and when I pulled the tube, the plate pin remained in the socket. Luckily, I have another 6C4, and when I dropped that in, I finally was rewarded with the sweet sounds of static.

The fly is also good! After capping, HV came up right away! Now, to hook up the crt (really wish I had a mini test crt right now) and see if I am getting a picture!

I had the picture tube hooked up, and was rewarded with an out of sync image, but audio and video were of reasonable quality. I removed the crt and flipped the chassis again, changed a few resistors and micas, flipped it again, reinstalled the crt and power up, this time, the 5u4 flamed out. I quickly ID'd a short in the horizontal section, so I dreaded that the flyback was out.

Checking a little more closely, I found that the width coil was missing the inner former tube, making it flop around loosely on its leads. The threaded steel wire that slides in and out of the coil was shorting to it, the adjuster being grounded to the chassis. Essentially, the 5u4 was shorted dead to ground.

With the problem identified, I slipped a cocktail straw into the coil as a new form, and glued the coil back into place. Now the width coil is electrially sound, and still adjustable.

http://i288.photobucket.com/albums/l.../zenith011.jpg

Nice troubleshooting and fix :beerchug:

I can only make a quick post, but perhaps someone here will know:

I can't get vertical lock, I will cover some of the other details on this later, but one of the components in the vertical includes a mysterious "vertical integrator" the parts list only describes it as this, and the schematic includes no values as to what is in this part. Anyone with any ideas on what Zenith used to make their vertical integrators?

They tended to use this circuit
http://www.videokarma.org/attachment...3&d=1298355433
The resistor part tends to drift to too high resistance.