Zenith 24h20 Porthole

[leadlike]

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.....

[John Marinello]

No pic.

[miniman82]

Let's try this again...

[VintagePC]

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!)

[leadlike]

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...

[Eric H]

Originally Posted by leadlike

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...

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.

[VintagePC]

Originally Posted by leadlike

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

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!

[leadlike]

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.

[leadlike]

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:



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!

[charokeeroad]

Originally Posted by VintagePC

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!

Ok I'll bite. What's the secret? sounds like a possible new thread. "The Black Art of Coil Rewinding Exposed.."

[leadlike]

Well, I found a resistor that had gone low, and replacing that one bumped the voltage up to about 60 volts. But just then, the width coil flashed over and caused the flaming 5U4 effect again.

So....completely disassembled the width coil this time. It is toast. The coil is in two sections, with a center tap, I believe, and one section is just destroyed. This may have been what took this set out of service so long ago, as I found a few other attempts at trying to shore up this coil before I used that cocktail straw.

I'll try to give more details later, but now I have to see if I have anything close to this coil on my parts sets...

[VintagePC]

Originally Posted by charokeeroad

Ok I'll bite. What's the secret? sounds like a possible new thread. "The Black Art of Coil Rewinding Exposed.."

Not much really - go slow, be careful, and have a fair amount of wax handy to save your progress every so often...

It worked for my oscillator coil (my Fleetwood thread). The big thing is the number of turns and the direction in which you wind that need to match. In the case of my Fleetwood, I couldn't get the number of turns, so I opted to get the total length of wire, and wound it in as close to the same winding pattern as I could - and it worked!

[Electrohome]

The above post is spam-please remove-thanks.

[Eric H]

Originally Posted by Electrohome

The above post is spam-please remove-thanks.

Done

[bandersen]

Nice troubleshooting and fix