I finally found one of these. It uses a glass CRT, which tests good (up to 350/1000 on the B&K 420 after leaving it on at 6v for about 5min)

I have the back, but am missing all the knobs. Does anyone have pictures of what the knobs look like? For all I know, I might even have them in one of my boxes of knobs.

The guy I bought it from said someone came to pick it up last week, was all ready to buy it, then said he wanted to fish tank it, and he refused to sell it to him!

Looks cool would love to have one of those one day.

Try that Mike Koste feller-"Gobs of Knobs" over yonder at AK...

Adam, have you been able to determine the year and model nbr I might have a couple extras, but would verify against the year/model nbr.

1949
chassis 28F20/21/22
which corresponds to sams # 64-15
which gives the following corresponding model #s: 28T295, 28T960, 28T961, 28T962, 28T963
From the pictures given, I don't have the 28T295 (which is a table model) or the 28T960 (which is a different console)
Anyway, it looks like they all use the same knobs, just different colors.

I can almost make out the knobs well enough from the pictures to go check and see if I have them now.

I think I might have found the smaller knobs, I know some of these Zeniths used these red fine tuning knobs, and I also found these brown ones that are the same size and shape. (The ones with the longer shafts won't fit unless I cut them down) See pic.

If that has the original CRT, it'll be a 12KP4, aluminized. Great performer.

I have a 28T925R. Have a couple of extra knobs you are welcome to. I'll have a look tomorrow and let you know. The smaller ones in your photos are not the same but will work in a pinch til the correct ones come along

Hey! I have that same set! Here are the knobs of the set. Sorry for the lousy quality - old mobile phone....

The CRT is so dusty and dirty I can't read anything off of it. I can see where it says Rauland, which is what I believe Zenith called their picture tubes, so there's a good chance it is the original tube.

I have a 28T925R. Have a couple of extra knobs you are welcome to. I'll have a look tomorrow and let you know. The smaller ones in your photos are not the same but will work in a pinch til the correct ones come along

Thanks! Let me know what you come up with.

Hey! I have that same set! Here are the knobs of the set. Sorry for the lousy quality - old mobile phone....

Thanks for the pics. Unfortunately, I don't have those. Can I see the smaller ones? I have lots of those little knobs, I might still have the right ones.

Hi Adam..here are some pics of the channel selector ( one large knob), and the fine tuning knob that sits under the on off switch....I ll post the others shortly

here are a couple of the on off knob, which lays on top of the fine tuning knob, and the four minis, which are for horizontal vertical, fine tuning and brightness...the knob on the previous post that was identified as fine tuning, is actually for contrast.

I have two extra of the mini knobs, and I might have an extra channel selector. I have pm d someone else who was looking for the channel selector, but have not heard back from them, but will give them a few more days.

Thanks for pulling those out. I have a bunch of the smaller ones in a lighter color. Which controls take the knob with the dot, and which the knob with the edge sticking out? ... Actually, the hole on the ones with the edge is too small, so is the hole in the ones with the longer shaft, so only 3 of those fit.

I ll measure them the width of the holes this eve. Its the same knob set that ha1156w posted

The knobs with the dots are under the fold down tray where the horizontal. Vertical. Brightness and fine tuning. The two dotted on the right side look correct. The one on the left looks slightly different. My model, the tabletop, has all dark brown, but I have seen pics of the consoles with white minis instead of brown. Have also seen consoles with brown channel selector, white contrast with a brown on off over top of it, and all white minis under the fold down lid. Its difficult to say but I'd say two of the three little white ones look correct.

I have this colorful assortment of what I think are Zenith knobs. If anyone needs some, just let me know.
http://farm9.staticflickr.com/8225/8365944817_92dff14a12_m.jpg (http://www.flickr.com/photos/70039806@N00/8365944817/)

I posted a close up of the small knobs some time back in this thread here: http://videokarma.org/showthread.php?t=255808&highlight=zenith+porthole

http://videokarma.org/attachment.php?attachmentid=176497&d=1349490340

Are the catches broken on your control doors? Mine was missing one when I got it and the other has since fallen off, they were either soldered or glued on the inside of the doors.
If anyone has a good picture of what they look like I'd appreciate it.

All 3 of my small knobs with the dot are the same, that picture just makes the left one look slightly different. All of the others I posted in that pic have the wrong size hole (too small). The catch on my left door is good it appears to be soldered on, the right one is missing. Here's a pic of the left one.

Thanks for pulling those out. I have a bunch of the smaller ones in a lighter color. Which controls take the knob with the dot, and which the knob with the edge sticking out? ... Actually, the hole on the ones with the edge is too small, so is the hole in the ones with the longer shaft, so only 3 of those fit.

The shorter knobs look like the ones on my '51. The ones with the tabs were
for the horizontal. There was a small tit that that tab would hit, limiting it to
just less than a full turn. It rotated a slug, rather than a pot.

Well. Its up to you Adam. As I mentioned I have seen consoles with all white minis As you have three it might be easier to locate one of those as opposed to two browns. I'd see if the person who posted. Pic of their console earlier in the thread, can check and see if he has brown or white minis under the face plate. Let me know which direction you decide to go, white or brown

Ross

It soooo kills me to say this...I have a Golden Lab, just over a year old. Beautiful dog, but still very much a puppy. Yesterday, I left the knobs in a ziplock bag on my kitchen counter. Today, I got home from work and found a ripped up bag all over the kitchen and a few of the knobs laying on the floor.

As it stands I am now looking for the same knobs. Grrrr. My fault, I should have put them immediately back on the set afterwards, but got distracted. I have found one mini knob and the remaining 5 I have not found as of yet, but will keep looking over the weekend. The other thing I can do is, go outside with him tonight and tomorrow and keep an eye on things ;-) Its a dirty job, but nothing a good disinfectant wont cure, should they appear that way. Update, he got into the chess set too.

Live and learn.

I thought you would say that you found them chewed up. Now, it goes to a different level!

Update. Have found two more minis. Under the couch. At least they are probably just in the house, thus preventing a full on dissection tomorrow

Sounds like another thrilling episode of as the Knob turns..
Thank You Marty

Good one Marty. I feel like such a knob. The good news is after a thorough once over I found the remaining knobs in various places in the house. So everything is back in order. Adam if you are interested in the two brown knobs, let me know an I'll send them out to you for the cost of postage

Width of hole on rear of knob is aprrox 1/4 inch

Ross

the two extra knobs have been spoken for.

I finally started working on my porthole. I thought it was interesting to note a mistake by someone working on this long ago. Look at the resistor in the pic with the arrow pointing to it, it's hooked to the wrong section of the can. What it did (now looking at the schematic) is to connect a 27K resistor parallel to that 20uf capacitor connecting to the tube side of the vertical output transformer. I wonder if this set ever really worked like that. Now I'm going to have to check over the whole set following along in the schematic to make sure there aren't any more similar mistakes.

Ugh, I hate when that happens. I'm glad you caught the mistake and good luck!

Well, this tv was really messed up. Someone (probably back in the 50s looking at the parts he used) replaced about half the resistors in this set, and often used the wrong values and hooked one end up to the wrong place, sometimes even hooking it around the wire of the old resistor without any solder. He also changed some of the cans (with not exactly the same ones) and screwed up trying to rewire. And a large number of the resistors (both original ones, and changed ones) were bad. Tubes were even in the wrong sockets.

I went through this set component by component with the schematic, and am now just waiting on a order of resistors to get any further. That large 20W horiz damper filter resistor was open among others I didn't have in my parts drawer. I haven't tested the tubes yet either, or put the electrolytics in the power supply chassis. This set's also going to need a lot of cosmetic stuff too (refinishing the cabinet, getting rust off the top of the chassis, new dial cord) but I'm just working on getting it running first.

Here's a pic of what the chassis looks like now, and some of the "classy" work left behind by the last guy to work on this from the power supply chassis.

Any ideas what I can replace this bad coil with? (circled in the schematic) All I have is the Zenith part number: S-15126 and 6ohms.

Any ideas what I can replace this bad coil with? (circled in the schematic) All I have is the Zenith part number: S-15126 and 6ohms.
You could simply jumper it temporarily till you can find a replacement. It's a peaking coil whose sole function is to 'tailor' fine detail in the pic.
I've tried jumpering peaking coils just to see if there's any difference, and usually there's no discernable difference whether the coil is jumpered or not.

I spent some time cleaning the chassis. That power supply chassis was so rusty that even after cleaning it with the naval jelly, sandpaper, etc... I still decided it would look better if I painted it. (I'm going to dig up a junk can to replace that missing one)

(With that coil jumpered) I'm now getting a nice full blank raster - no sound. The sound comes off before the 1st video amp tube, so I'm thinking the problem has to be back in the tuner to be affecting both sound and picture.

So now does the brightness control work correctly?

So now does the brightness control work correctly?

Yes. (It's all the way up in that picture)

The sound comes off before the 1st video amp tube, so I'm thinking the problem has to be back in the tuner to be affecting both sound and picture.Have you checked anything in the audio section downstream from that point? If you turn on your soldering iron and touch it to the wiper (center terminal) of the volume control, do you hear a buzz?

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I haven't gone through it systematically yet, to absolutely eliminate anything in the sound portion of the set, but I was getting static by tapping the AF amp tube.

I wouldn't mess with the tuner until you have eliminated the sound section and other downstream circuits to confirm that they're all hunky-dory.

Phil Nelson

Now that I finished with that newer Zenith, I'm back trying to fix this one...

I poked around with the scope and didn't see any video or audio signal anywhere. Then what I tried was to set just a regular signal generator (with the AF modulation on) to the IF frequency, then hook it into the grid of the 1st audio and 1st video IF tubes, just to see if a signal would get through. And it did, I got buzzing in the audio, and those lines on the screen.

But the problem still turned out to be not in the tuner, but in getting power to the tuner. That choke coil I circled, L19 is open. What can I replace this with? All I have is the Zenith part number S-15128 and 1.5ohms, it doesn't give me the inductance, or any equivalent part numbers.

I swapped in a coil (of unknown value) and got: weak sound, crappy video, and sync that won't stay put (H or V). I tried several different coils and got the same results, so even though I'm not quite sure what to put for that coil, I'm fairly sure the problem I'm looking at now lies elsewhere.

I'm going to poke around the AGC amp tube and check the voltages, but I have a suspicion, with all the other goofy stuff that was done to this set, that someone got in there long ago and twiddled every adjustment they could find and goofed up the IF alignment, video and audio.

I swapped in a coil (of unknown value) and got: weak sound, crappy video, and sync that won't stay put (H or V). I tried several different coils and got the same results, so even though I'm not quite sure what to put for that coil, I'm fairly sure the problem I'm looking at now lies elsewhere.

That's correct. The inductance value is not critical, since the coil serves no other purpose than as a choke. In fact you could probably jumper it completely and never know the difference.
...I have a suspicion, with all the other goofy stuff that was done to this set, that someone got in there long ago and twiddled every adjustment they could find and goofed up the IF alignment, video and audio.
Actually it does not show symptoms typical of video IF misalignment, namely strong
smearing-out and ringing of fine detail in the pic. Fine detail looks pretty crisp. That's not to say the audio IFs haven't been messed with, though.

Well, this one stumped me for a long time. I even went and replaced loads of resistors that tested good. But there turned out to be 2 problems with the picture:

1. Looking in the 1st schematic I posted, that C7B I put in backwards:D, this caused the "crappy video", strangely it didn't explode, but I could see it was bulged out and I put in a new one.

2. And this was the really tricky one, what was wrong with the sync, looking in the 2nd schematic pic I posted, the cathode of that sync clipper tube needs to go to ground, not to the heater, otherwise the 6V AC on the heaters seems to get mixed in with the sync pulses. Connecting it to ground fixed the problem.

This didn't trip me up like the other problem, but I also pointed out in that schematic on the 6SH7, pin 5 is the cathode and pin 7 is the heater, the schematic has it the other way around. This tv had so many resistors wired to the wrong place, that I basically rewired it following the schematic almost like putting together a kit. The cathode of the 1st sync clipper tube was probably wired correctly to ground to begin with.

Next pic is the picture as it stands. The horiz still takes about a minute before it's really stable, but then it locks in good. No issues with the vert at all.

------

Now for the sound, first I thought to put the signal generator on the grid of the 1st audio IF tube, and just tweak all the IF transformers for loudest volume, but it was still pretty weak.

Then I hooked up the full blown early 1950s RCA sweep generator alignment set up I have and was able the get the picture on the scope for the discriminator transformer alignment just like it should be (ignoring the fact that for some reason the marker-adder decided it only wanted work set to reverse polarity) But, when I moved back to the 3rd IF transformer I could see the peak was set to twice the IF frequency, and I couldn't get it down much below 31MC. The sound section is in the 3rd schematic I posted...

Now for the sound, first I thought to put the signal generator on the grid of the 1st audio IF tube, and just tweak all the IF transformers for loudest volume, but it was still pretty weak.

Then I hooked up the full blown early 1950s RCA sweep generator alignment set up I have and was able the get the picture on the scope for the discriminator transformer alignment just like it should be (ignoring the fact that for some reason the marker-adder decided it only wanted work set to reverse polarity) But, when I moved back to the 3rd IF transformer I could see the peak was set to twice the IF frequency, and I couldn't get it down much below 31MC. The sound section is in the 3rd schematic I posted...

Don't know if you've checked this yet, but while I was working on my 12" porthole I discovered the same issue in the sound IF's that I had already found in Zenith's table model sets of that vintage. They used silver mica wafer caps in the IF cans that started to break down and leak(silver mica migration). I had to disassemble two of them and remove the damaged mica sheets and then add external mica caps to the base of the IF cans. That solved the problem in my case.

Bob