Starting to go through the pile of TVs I have to restore and decided to start with this Zenith model G2322 chassis 23G22 aka "Claridge"

It has an oddball semi-hot chassis where the top plate is hot, but is insulated from the rest of the chassis. The tubes are series strung with a power transformer just for B+ .

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This version has a metal cone 12UP4 CRT which made me nervous as they are often bad. I got lucky though and it test very good :)
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Next up I'll slide the chassis out for a closer inspection.
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Oh, was the wacky year porthole with the funky chassis? Yeah, never understood those. I suspect Zenith gave up on portholes in general because, as good a set a Zenith was, the styling was a turn off, as everyone started to have an idea of how a TV “should” look…

Note the UL sticker. Approving everything is nothing new to them…

This is an early model from 1949. I think they made them until 51 or 52. A bit after everyone else has gone rectangular. Seems like they went their own way with both the electrical and cabinet design. Even had their own FM detector tube (6BN6). Must have cost a bunch in R&D.

Oh, was the wacky year porthole with the funky chassis? Yeah, never understood those. I suspect Zenith gave up on portholes in general because, as good a set a Zenith was, the styling was a turn off, as everyone started to have an idea of how a TV “should” look…

Note the UL sticker. Approving everything is nothing new to them…

Porthole sets were the logical result of, round CRTs, no measurement standard, and a market starved for bigger screens. You can claim more square inches with a double D mask than a rectangular mask, and even more still if you dispense with the mask and show the whole CRT face.
Around the time Zenith and others gave up the porthole sets larger rectangular tubes were reaching market which made portholes pointless.

I think the idea of the 6BN6 was 2 fold...1.) make something that nobody has a patent on so the difference between paying royalties and receiving royalty payments from other companies pays for the R&D several times over. 2.) Make a tube that is both detector and first audio to reduce tube count and complexity/cost.

First time I saw one of those sets the thing that stood out most was the tuner. I was used to seeing the small Admiral turret tuner but this one was impressive!

I picked up the same set at Kutztown a few years ago all restored. Low contrast now though. I'll be watching this.

I pulled the chassis yesterday and here's what I found.


All knobs are present including the five under the door. (I also have the metal back)
The fine tuning dial string is broken :(
The channel selector is frozen.
The CRT support spring has broken loose because a post broke off the lucite CRT support. (I may have a spare).
Very little servicing has been done. Looks like only one or two paper caps have been replaced.



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Replacement caps?
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Did you decide if the CRT was a replacement or not? I was thinking that it's possible the set was removed from service when the original developed an open in the base and so you've got a relatively low-hour original CRT. Looking forward to find out!

That CRT looks like it's a Sel Son brand. I thought early Zeniths likely came with a Rauland made CRT, which if I'm not mistaken Zenith later owned?

Correct on both counts. Yes, I do think it is a replacement.

I finally got around the recapping this beast. The power supply had seen some work and was a bit of a mess. One open power resistor and another had replaced with the wrong value.

https://live.staticflickr.com/65535/53086804191_e1ab66ee93_c.jpg (https://flic.kr/p/2oT6Knr)

I cleaned that up and used adapt-a-caps to replace the 3 multi-section electrolytic caps.
https://live.staticflickr.com/65535/53086237757_ca16805f91_c.jpg (https://flic.kr/p/2oT3QZk)

Here's a peak inside the giant tuner.
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First power up went well - no smoke and the 5AXP4 test CRT lit up.
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I unmounted the PM focus assembly which cleared up the self-focusing 5AXP4 image.
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It's mostly working, but I have to max out the contrast and the image is noisy.
https://live.staticflickr.com/65535/53087298693_af2c1289bf_c.jpg (https://flic.kr/p/2oT9hnk)

Next I wanted to see what the full sized CRT could do. Here it is all cleaned up.
https://live.staticflickr.com/65535/53087208380_32be495962_c.jpg (https://flic.kr/p/2oT8Pwd)

Gave the chassis a CLR wipe down too.
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It lives! Not at all fun to be around that metal cone when it's running.
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Normal mode.
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Expanded mode
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I've swapped all the tuner and IF tubes and rechecked my work. Nothing made any difference.

I'll do a little signal injection next starting at the video amp and working backwards.
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I was able to get a much better image by injecting a composite signal into the grid of the 1st video amp.

Injecting an IF signal into each of the four IF stages seemed to produce a good image as well. I say seem because it's possibly my injected signal was larger in amplitude than a normal signal would be.

Also tried driving the AGC bus directly with a variable DC power supply but it really didn't do much. If I went slightly above or below 0 volts, the image would disappear. Schematic shows 0.1 volts on the AGC bus during normal operation. I'm really not sure what the normal range of this voltage should be.

Finally, went over the tuner again but didn't find any issues.

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You could try comparing the tuner signal level at the input to the 1st video IF to what you're directly injecting there. Something needs to give. Maybe use the output of the video detector as the reference so as to not load the IF signal.

Good idea. I just bought the Sams Photofact for this chassis which has some useful info. For example it says if the AGC delay control is set properly, the signal at output of the detector should be 3.5 VPP during normal operation.

I'll start by going through the voltage and resistance chart for the tuner and IF first though.

I'm also curious about the 470pF cap that couples the output of the tuner to the IF.

Word of warning. The AGC delay (center of photo), sound buzz and channel LO adjustments are all very close to the metal CRT cone. Take great care when adjusting them with the TV powered up.

I got a bit careless and was bitten on the knuckle by about 9,000 volts. No damage done at that low current, but it will wake you up.

https://live.staticflickr.com/65535/53100367432_f54e293caf_c.jpg (https://flic.kr/p/2oUigfq)

I picked up a copy of the Sams Photofact and starting going through the resistance chart.
Found a problem in the very first tube. Hidden down inside the tuner I found a fried 1K resistor that feeds the plate and screen of the 6BJ6 RF amp tube. It was only measuring a couple 100 ohms in circuit and fell apart when I removed it.

I really thought I had it but unfortunately, replacing it made no difference at all. Might even be a little worse now. I'll keep digging.

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Word of warning. The AGC delay (center of photo), sound buzz and channel LO adjustments are all very close to the metal CRT cone. Take great care when adjusting them with the TV powered up.

I never got why TV manufacturers didn’t think this stuff through when designing these sets. Especially with the metal tubes, where the cheaper sets often omitted any insulating cover.

I’m wondering if that was a factor in the downfall of metal CRTs - servicemen hated them. Actually, the metal CRT was a weird idea anyway. I don’t know why it came about in the first place. Maybe someone at RCA was bored one day…

Maybe it was the push for bigger screen size before the all-glass technology was mature enuff for it. :scratch2:

RCA spent 13 years developing the metal cone CRT. Reduce cost, reduce weight, increased screen size.

You can read all about the introduction of the 16AP4 here: https://worldradiohistory.com/hd2/IDX-Service-&-Sales-IDX/Archive-RCA-Service-IDX/IDX/RCA-Victor-Service-News-1949-07-OCR-Page-0006.pdf

Another great article here: https://worldradiohistory.com/hd2/IDX-Site-Technical/Engineering-General/Archive-Electronics-IDX/IDX/40s/Electronics-1949-05-OCR-Page-0085.pdf

and application notes: https://www.one-electron.com/Archives/RCA/RCA-AppNotes/RCA%201949%20AN-140%20Recommendations%20for%20Support%20and%20Insu lation%20of%2016AP4.pdf

Went over the tuner again check all the voltages, contacts, etc - found no issues.
Found an open peaking coil on the video amp. Bridging it made no difference :sigh:
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Just picked up this TeleMatic Tuner-Mate KT 730. It has a 44MHz IF you can inject into a TV to substitute for the tuner. Maybe it will help?

Really it shouldn't be any different than the signal injection I already tried, but it's fun to play around with vintage gear.

Seems to me the problem has to be in the tuner or early in the IF. The video signal at the CRT is fairly strong but the signal to noise ratio is terrible.
AGC voltage is also very high. For example, the grid voltage on the tuner RF tube should be around -0.5 volts, but I have positive 0.5 volts.
The signal is just not getting through cleanly somewhere.

https://live.staticflickr.com/65535/53105256522_9b9551cb28_c.jpg (https://flic.kr/p/2oUJjB5)

That positive grid bias may be a clue.
1) Have you tested the tuner and IF tubes?
2) How about injecting a negative voltage and seeing if the picture clears up. If it does, then you need to look for a fault in the circuit that supplies that bias voltage.

I've tested and swapped out every tube several times. If I inject a negative voltage the image fades away. Seems the AGC is asking for as much gain as possible due to a weak signal coming through the IF.

Something else odd I noticed is scoring on the inside of the tuner cover. The contact fingers are slightly worn down as a result.

This thing is really solid made with thick, formed sheet metal with no room for adjustment. I get the impression it's been this way since it was made.

Anyone with porthole experience see something like this before?
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What happens to the picture when you adjust the AGC delay?

The gain varies. I have it maxed out for the screen shots I took.

I don't think I have seen any contact scraping on the tuner cover before on my porthole sets doing tuner cleans.
You may want to look for anything mechanically out of whack causing the scraping.

The gain varies. I have it maxed out for the screen shots I took.

I don't know the details of the AGC delay circuit in this set, so I will comment hypothetically.

Hypothetically, the AGC delay is supposed to keep the RF AGC from operating for input signals below a certain level. So, for example, going from zero to 1 mV RF input, the RF stage should have constant max gain while the IF AGC voltage varies the IF gain from maximum to some reduction as required to get normal detected video level. Then above the delay set point (1 mV in this example) the RF AGC starts to vary to reduce gain in the tuner as well as in the IF.

Can you put two voltmeters on the RF and IF AGC voltages and supply a variable level RF input to see if there actually is any delay action?

Another thought: could there could be a bad RF connection at the tuner input?

The RF and first 3 IF stages use the same AGC signal. This design used an AGC circuit gated by the horizontal sync pulse. I believe the delay determines how long the AGC tube conducts after the start of the sync pulse.

You can get the full Zenith service manual from the ETF here: https://www.earlytelevision.org/pdf/zenith_service_manual_tv-5.pdf

Thanks. I downloaded the manual.

The AGC Delay control is a variable voltage divider between 150 volt supply and ground, connected to the AGC amp cathode. It looks to me like it mainly sets the threshold of IF output level for the AGC amp to conduct. It doesn't conduct "until" the IF output reaches a set level. So, it's an AGC control - forget the "delay" word.

Afraid this gives no hint of what the problem is.

Those tuner contacts rubbing on the back of the cover plate are highly suspect.

They are and I went over all the fixed and moveable contacts.
They're fine.
Also went over all the coils in the channel strips.
They're fine.

However, while making all these checks I must have bumped something because a tuner tune went dark. Now how is that possible when it's a series strung set? Well some of the tubes (including those in the tuber) draw their filament juice from a power transformer.

So I wiggled the tube and, viola, a clear picture emerged! Bad tube socket strikes again!

Now the tube had been glowing when I was getting a crummy image so I expect it was the grd, cathode or plate that was making a high resistance connection.

Thanks for all the thoughts and suggestions.
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Woohoo! I hate bad connections.

Bob, only recently, I have gotten back into working on my televisions that have been in queue for literally years. I have been concentrating on tube amplifiers. What I have found is that so many times, on initial power up, monitoring the filters, etc. I have no signal pass at all.

Tube sockets are always a problem with those amplifiers. Now that I have worked on the Pilot TV-37 and RCA 630TS, one thing that I always do is clean each socket as part of the drill. It has "burned" me too many times.

Congratulations on another nice project. I have a Porthole in queue right now, but the Admiral 19A11 just made it to the bench and that is front and center!

Good on 'ya, Mate!

Amazing how these things take us down the rabbit hole only to find it’s something so simple! I’ve been working on a focus issue with my GE Locomotive and I’ve suddenly lost the video and sound. I’ll bet something got knocked loose after I flipped it over a few times. The tv gave me my first opportunity to use my 5” technician crt. A lot easier than manipulating a chassis with a 10BP4 in it!

one thing that I always do is clean each socket as part of the drill.Amen. That's why my "First Steps In Restoration" article has a section on cleaning tube pins and sockets:

https://antiqueradio.org/FirstStepsInRestoration.htm

It's such a simple and obvious step, but some folks skip it -- maybe 'cuz they're in a hurry.

Regards,

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

Well in my defense it wasn't a dirty socket, it was a damaged socket. I did make the assumption that since it was ceramic, it was high quality and making good contact, but it turned out the one of the contacts was loose. Possible from having a bent tube pin inserted. I was able to tighten it up.

I wrapped up cleaning the cabinet last night and put it all back together.

The cabinet was rather dirty and had the ubiquitous white specs. Insect poop? GoJo to the rescue followed by OZ cream polish.
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I found some new foot at Home Depot that were a surprisingly good match for the originals.
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Finally, spent a frustratingly long time getting the screen geometry right. Looks good in both normal and expanded modes.

https://live.staticflickr.com/65535/53156218468_3ae02263f9_c.jpg (https://flic.kr/p/2oZevPj)

I did touch up the ion trap position to eliminate the shadow after I took these photos.
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All worth it to see a pre-Star Trek William Shatner looking so young and beautiful! Watched your video last night and the dirt that come off the cabinet was epic! Terrific looking 1949 TV with a great picture. Good to know that kilovolt charged CRT is back where it belongs!!!

Not so exciting maybe, but here's the original metal back in very good condition.

https://live.staticflickr.com/65535/53157695756_817d912aef_c.jpg (https://flic.kr/p/2oZn5XN)