View Full Version : 1951 Zenith 16" Porthole


Radiotronman
08-23-2016, 10:49 PM
Like many guys, I like to restore more than one set at a time. A friend of mine found this same cabinet in blonde with no chassis. It's near mint and the seller wants to get rid of it so a deal is being made to acquire it. I thought what am I going to do with it? Put the chassis in my mahogany set into the blonde cabinet since it's worth more? Then a few days went by and I found another seller wanting to sell his zenith chassis from a trashed cabinet. So now I'm trying to get a deal on that chassis so I have two complete sets. In the mean time I'm going to go ahead and restore the chassis I have. I'll order parts for my RCA portable I'm working on to save money on shipping by ordering all of the parts together. The chassis is 24H20 with a 16" metal tube, 16GP4 I believe. Like my other 16" I restored, the tube tests bad, but still lights up with a very watchable brightness to it. It also has the seperate power supply chassis. I'll irder all of the parts in the next week or two and get at it.

Radiotronman
08-23-2016, 10:56 PM
Here is a picture with the doors closed. I like the more modern look to this over my other set which is more traditional. It also has very nice piano hinges down both full length doors and thick wood slats in the speak area. This set had many scratches, but good enough not to refinish. Maybe I'll use Howards restore a finish or just som red stain. The thread on how to display your sets has inspired me as I finish my basement in the next year. I decided I'd like to display and have working my better sets, like this one. If I can't make a deal on the chassis, because the seller is deciding on keeping it it not, then I may display it in the blonde cabinet.

Radiotronman
08-23-2016, 10:58 PM
Here is the chassis with the 16" metal coned CRT. I've got a few portholes now, but still yet to come across a 19" porthole.

Radiotronman
08-24-2016, 09:46 AM
Here is the underside of the chassis. I replaced a few of the capacities that I had. It looks pretty much untouched. It's amazing how much lighter this chassis is with a metal coned CRT. But I think they made up for it on the cabinet, as it's super heavy and every piece of wood on it is an inch thick.

dieseljeep
08-24-2016, 10:32 AM
Here is the chassis with the 16" metal coned CRT. I've got a few portholes now, but still yet to come across a 19" porthole.

The set uses the old 52 degree 16EP4, not the newer 16GP4 70 degree CRT.

John Marinello
08-24-2016, 08:45 PM
The set uses the old 52 degree 16EP4, not the newer 16GP4 70 degree CRT.

Wrong, x2.

24H20 chassis use the 16GP4.

The 16EP4 is a 60 degree tube.

Radiotronman
08-24-2016, 10:48 PM
The picture us a little dim, but if you look on the upper right hand if my cabinet tube layout, it lists the 16GP4 for both 24H20 and 24H21 chassis. The schematic for this set (SAMs 120-13) also list it for the 16GP4.

dieseljeep
08-25-2016, 12:28 PM
Wrong, x2.

24H20 chassis use the 16GP4.

The 16EP4 is a 60 degree tube.

If I'm going to be wrong, I do a good job of it!
I looked at the Riders #6 coverage for that chassis and it looks like it was the last run of the portholes. They did have to switch to a 70 degree sweep to incorporate the 16 and 19" CRT.

John Marinello
08-25-2016, 03:15 PM
The picture us a little dim, but if you look on the upper right hand if my cabinet tube layout, it lists the 16GP4 for both 24H20 and 24H21 chassis. The schematic for this set (SAMs 120-13) also list it for the 16GP4.

That's just a tube layout, and covers the 24H20 (16") & 24H21 (19") chassis,
which were similar. If you look at the CRT, It shows 16GP4 OR 19AP4.

The 16GP4 is a 70 degree tube, and the 19AP4 is a 66 degree tube.

Radiotronman
08-30-2016, 07:36 PM
Finally got around to placing my order for capacitors and decided to recoat the flyback and clean the dust inside the cage area. The flyback had pieces of the original coating laying at the bottom which I removed. I recoated it with rtv sealant and I'll reinstall the casing once it cures over night.

Radiotronman
08-30-2016, 07:38 PM
Surprisingly, there was also a wire on the flyback that wasn't even soldered on! It was just wrapped around the loop connector. So I cleaned the terminal and soldered it on. I don't know how it worked all these years without a secure connection? It was loose when I touched, just floating.

Radiotronman
09-07-2016, 07:03 AM
Just an update after most of the recapping is done. The hv is low, but I do have a raster with a picture!

John Marinello
09-07-2016, 02:07 PM
What is your HV reading? Not sure what to make of your pic, is it just dim, or blurry also? What happens when you increase brightness, does the pic bloom, then extinguish? That would be a symptom of low HV. Is your ion trap adjusted properly?

Radiotronman
09-07-2016, 04:27 PM
My hv probe somehow broke so I don't know the voltage. It doesn't bloom when the hv is turned up. The CRT tested bad, but so did my other 16" and it was very watchable. There are a couple more electrolytics I still need to replace because I sinehiw didn't order them with the rest of the cap order. The people brightness is turned all of the way up in the picture.

Radiotronman
09-07-2016, 04:28 PM
I also tried adjusting the ion trap, it's in the brightness position also.

John Marinello
09-11-2016, 03:00 PM
Well, you could do what the old-timers used to do... pull the anode & see how
much of an arc you can pull... About an inch, you should be fine.

Radiotronman
09-19-2016, 01:50 PM
I ordered the remaining caps I needed to finish the recap, so I can move forward and address any low hv issues.

Radiotronman
09-27-2016, 09:19 PM
A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

Radiotronman
09-27-2016, 09:24 PM
Is the set with video.

EdKozk2
09-27-2016, 11:24 PM
A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

I may be wrong, but one time I got an image like yours and it was because I had the ion trap and focus coil/ magnet in the wrong place with respect to each other. It could also be AC getting into the DC at the CRT. Reminds me of old time video scrambling. Did you finish the recap?
Ed

Radiotronman
09-27-2016, 11:56 PM
Yes, I finished the recap. Not sure what to make of it or to do. This set us so close to being done.

bandersen
09-28-2016, 10:12 AM
Ion trap magnet could be weak or flipped around backwards.

Electronic M
09-28-2016, 10:55 AM
Part of me wonders if the door knob cap might be open.

Radiotronman
09-28-2016, 12:27 PM
I've tried multiple ion traps and flipped them around and no change. Could it be a bad door knob cap? I've never seen a bad one.

Electronic M
09-28-2016, 02:11 PM
I've heard of them shorting, but can't recall an open one. To me it looks like either the gun drive or the HV is varying across each horizontal line (which could be caused by an open door knob)...That or it is an electron optics problem, but you've checked the trap, and there does not seem to be a focus coil IIRC, so varying voltages seem more plausible.

John Marinello
09-28-2016, 11:42 PM
A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

Try adjusting the centering control... it's that tab thingy between the focus coil
and the yoke.

Radiotronman
09-29-2016, 01:33 AM
I tried that control too and it didn't correct the issue. Good thought but I already tried it...thanks.

Electronic M
09-29-2016, 07:34 AM
If the set is focused properly currently and moving the coil does nothing, I'd like to know if adjusting the focus control away from proper focus changes how much of the picture is dark.

Radiotronman
09-29-2016, 11:36 PM
Adjusting the set out of focus made the picture less sharp, as expected it would. But didn't do anything to help brighten the left side of the screen.

Eric H
09-29-2016, 11:49 PM
I had this same problem with a Predicta Holiday, I don't recall what it was but it wasn't a mechanical issue, something getting into the video and blanking it on the left side I think

Try rotating the yoke and see if the problem follows it, if it does that would suggest it's in the video.

Radiotronman
09-29-2016, 11:55 PM
It's got obvious sync issues that I'll have to solve, but what is strange, is if I turn the volume all of the way down, the left side of the screen will get brighter, further over and the sync will somewhat stabilize. Any thoughts?

Electronic M
09-30-2016, 07:33 AM
It's got obvious sync issues that I'll have to solve, but what is strange, is if I turn the volume all of the way down, the left side of the screen will get brighter, further over and the sync will somewhat stabilize. Any thoughts?

Now this tells us something. Some sets used the audio output tube as part of the B+ voltage divider (instead of a dropping resistor they used a tube to put that energy to work). On sets with that form of stacked B+ if the audio output stage is miss-biased or otherwise not working correctly it will reduce B+ to other stages that it is the B+ dropper for. I recommend voltage checks in the audio out stage with the volume low and high...You may also want to scope the lower B+ rail that comes from the audio output cathode to see if it is not filtering well.

Radiotronman
09-30-2016, 12:04 PM
Ok great thanks! I'll start doing resistance checks on that chassis too where the audio output tube is.

dieseljeep
09-30-2016, 02:43 PM
Now this tells us something. Some sets used the audio output tube as part of the B+ voltage divider (instead of a dropping resistor they used a tube to put that energy to work). On sets with that form of stacked B+ if the audio output stage is miss-biased or otherwise not working correctly it will reduce B+ to other stages that it is the B+ dropper for. I recommend voltage checks in the audio out stage with the volume low and high...You may also want to scope the lower B+ rail that comes from the audio output cathode to see if it is not filtering well.
I honestly, don't remember Zenith using stacked B+. I'll have to consult my Rider's CD on the older models.
RCA used it on their lower-end models in the mid-50's, but not as much as some of the other makers. :scratch2:

Electronic M
09-30-2016, 02:50 PM
I honestly, don't remember Zenith using stacked B+. I'll have to consult my Rider's CD on the older models.
RCA used it on their lower-end models in the mid-50's, but not as much as some of the other makers. :scratch2:

I'm honestly guessing it uses that circuit based on the symptoms...If it is not using stacked B+ I can't imagine the audio pulling enough power to affect other circuits short of the output redplating (which I think he'd notice).

Radiotronman
10-05-2016, 12:27 PM
Checked all resistors in the small chassis and could not find any problems. Is this a horizontal issue or a problem with my yoke?

Kevin Kuehn
10-06-2016, 01:39 AM
I think if you rotate your yoke upside down it should verify if it's one side of your CRT(set up) related. If the problem moves to the other side of the CRT, it's likely something modulating your video or CRT brightness. It's a weird problem. :scratch2:

Radiotronman
10-17-2016, 11:56 AM
Ok, with a little help from my friend Sean, I found out why I was getting the symptoms I had. I neglected to reattach a black wire with an eyelet to the main chassis. It fastens with a quarter inch screw on the chassis, right next to the main power socket; an octal connector. I thought this was a mere ground, and had no idea it was connected to the audio output providing the stacked B+ that was mentioned earlier. I hooked this back up and got a perfect raster! I seem to remember making this same mistake on the last two-chassis porthole I worked on. Probably need to write this down...anyway, another porthole restored. Now I can put full ficus in my Dumont 15" tv.

Radiotronman
10-17-2016, 11:57 AM
Thought I'd take a picture with the set all back together! This is my favorite of the portholes and I'm excited to have finally finished it!

Paul Knaack
10-17-2016, 06:48 PM
Looks Great, excellent work.

Electronic M
10-17-2016, 09:22 PM
Nice!