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/ll179/leadlike/?action=view&current=zenith009.jpg&newest=1

No pic.

Let's try this again...

http://i288.photobucket.com/albums/ll179/leadlike/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.

The above post is spam-please remove-thanks.

Done

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. :yes:

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!

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/ll179/leadlike/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/ll179/leadlike/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?

Anyone with any ideas on what Zenith used to make their vertical integrators?

They tended to use this circuit
http://www.videokarma.org/attachment.php?attachmentid=169533&d=1298355433
The resistor part tends to drift to too high resistance.

Thanks! I may wind up making a new one.

Measuring voltages, everything comes up normal, with the exception of the plate of the vertical oscillator is way too low: I'm getting 45 volts on my digital multimeter, when my Rider's schematic puts it at 74 volts. The plate is only two resistors away from the B+ feed, so I replaced them as they were out of tolerance, but still get the same low voltage. Swapping tubes has no effect, either.

As it is, the picture I get "floats" vertically, it does a half-hearted attempt to lock, before drifting away again. The vertical flipping doesn't increase in frequency, there just doesn't seem to be any lock. Interlace is also poor. The effect is the same whether injecting signal at the video grid or through the antenna.

Check the grid of the vertical tube, it's probably high. When that happens the tube will conduct harder than it should, which drags down plate voltage causing more drop through the plate resistors. Fix the vert tube bias, and try again.

Riders provided no voltage values for the input grid of the vertical oscillator. The other half of the 6sn7 does have the values given, and they rate normally (59 volts for the plate, -15 volts for the grid).

But, looks like we're getting closer to the problem, so I'll be digging into the grid circuit here shortly.

BTW, the Riders is now available at the ETF site:

http://www.earlytelevision.org/tv_schematic_diagrams.html

Glad to see many more schematics up at that site, maybe someday I won't need all my Rider's binders...

Well, the schematic does show 2v at the cathode so I'd expect the first grid to sit somewhere around 0 or something negative. If the cathode is low, I'd suspect the cathode resistor and bypass cap. If the grid is high, look at that integrator or the 15k resistor next to it. Also check the voltage at the sync clipper plate and the resistors connecting it to the vert tube.

Well, checked all the resistors between the clipper plate (which is at normal voltage) and the vert osc grid and found a few out of tolerance ones. Voltage went up to 50v on the osc plate as a result.

Lifted the grid lead to see how much it was loading down the plate voltage, and it went up to 67 volts, so you're right, Miniman, the grid is improperly biased and loading down plate voltage.

Grid voltage sits at about .1 volts, cathode voltage is dead on at 2 volts. If I get time tonight, I will work on making Wa2ise's integrator and see what happens.

I figured as much. Find out why the 1st grid went positive, after you fix it the vertical should start working unless something else is wrong.

Regarding the integrator, see this thread:

http://www.antiqueradios.com/forums/viewtopic.php?t=75548&

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.."

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...

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!

FINALLY had some time tonight and rewound the width coil. From the closeup picture earlier in the thread, you can see that it is two spools. When I pulled the coil, the top spool crumbled in my hands. The center shaft on the spool burned up, exposing bare coil wires to the adjustable inductor, shorting the windings to ground, causing the 5u4 to flash over.

As the spool was gone, I could only make note of the winding direction of the coil, and strip it. The spool ends were still intact, if a little cooked (no conductive carbon, thought). So I made a properly sized cardboard tube for a new center shaft, and began winding magnet wire onto it (#36, seemed pretty close to the original) by hand. Once I got a good base laid down, I chucked the coil into my drill, and spun the rest on. The whole operation took about an hour and a half.

I hooked it up, and the set powered up. The coil didn't heat up, like the old one did, so I hooked up a video source and the crt, and was rewarded with a decent picture. Vertical hold is still twitchy, but it you leave it alone, it stays put. Sound is extremely poor. I suspect low bandwidth getting through, but adjusting the various sound and tuning controls still produces the same result with fuzzy highs and lows.

BTW, the old width coil measured 15 ohms, and the newly wound one checks out at 15.6 ohms! Not bad!

Otherwise, the picture looks decent, and the set is much easier to operate. I suspect that the bad width coil was heating up and loading things down a bit. Will take some measurements next.

If memory serves correct, the circuit RC network was called a "gimmick". The purpose is to cascade RC time constants, thereby re-shaping the sync pulse to improve vertical lock. In the old days, getting any watchable picture from weak signal was tough and Zenith seemed to excel. Has anyone ever seen this method used on the Horizontal pulse?

Getting closer-I can't quite get the image to fill the screen, and focus is a tad soft at the very fringes, but overall acceptable viewing from a few feet away. As the tube is a rebuild, it just may not be possible to get a perfect image from it. Also has a purple stain burned into the center phosphor, about the size of a half dollar.

Cured the hum in the audio (bad brand new lytic), and then started testing tubes to see if one was weak, and found that a 12AV7 had been used to replace the 12AT7 Noise Limiter/Audio takeoff stage. This was largely responsible for causing the poor audio, as well as some low frequency video smeering, and probably didn't help with the Hor/Vert locks, as they both function much better now. I still am getting some static in the image, cleaning tube pins helped, but I will have to pull the tuner apart and scrub down the ch. 3&4 strips.

I kept it on for 2 hours, and other than adjusting the vert twice in the first 30 minutes, it behaved nicely:

172501

Just curious: This set uses some odd tubes. I know Zenith used different tubes in their radios and tvs during the 60s, had they started this practice earlier? I see a 6C4, 6BN6s, 6CB6s, and a 6BF5 audio output. I replaced several of these from my stash, and the only ones I have are all Zenith branded replacements.

They did use those horible 6X5 rectifiers on their pre-war radios when most other home sets used 5Y3.

I rechecked voltages tonight, and yup, with that new coil in my weird loading issues stopped.

I also noticed why my screen adjustments weren't quite perfect: the focus electromagnet was replaced with a pm RCA assembly! The yoke also appears to have been replaced as well.

I cleaned up the pins of the channel strips, but you really can't get anything into the other set of contacts under the tube deck. So, I applied some strips of sandpaper to a tuner strip, and then racked the tuner back and forth over that channel, cleaning those hidden contacts. This operation cleared up most of the static I was getting in the picture.

Started in on the cabinet today as well. It had been stripped as found, so I applied filler and will try to lacquer this weekend.

172508

172509

The above spam made me laugh.

I'd recommend removing half the strips and rotating the drum until you can properly reach the fixed contacts for proper cleaning.

Yeah, that spam actually tried to have some relevance to the topic. I had tried a number of times to get into those fixed contacts, even following what you suggested by removing several strips. They are just too buried to still access that way. The whole deck can be removed, but I just don't think it is worth it. The solution I worked out seemed to do a nice job of getting that crap out of there.

I have two sets of e-caps in series without balancing resistors (2X33 and 2X47) what is the best way to calculate the resistor value? One manufacturer's data sheet stated just 10/C is a way to ballpark it, while others stated some fairly involved math is necessary. Finally, a Cornell Dubilier data sheet stated that they aren't necessary, as they generate uneeded heat and are more likely to fail than the caps.