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#1
09-15-2015, 09:28 AM
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Zenith porthole poor width question....
As shown, this is about all the width I can get out of this 12" Zenith porthole.
This morning, I heard about a trick. Apparently if you put a hv disc style cap across the damper tube it will increase picture width. Has anyone heard of this and knows the specifics?
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." 
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#2
09-15-2015, 09:55 AM
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Yes, they used to make a Damper width "cookie" - just plug the damper tube into the cookie, then into the set. In the cookie was just a low-pF cap, around 100pf or so.
I still have a NOS one, from Workman (before they were Workman, they were Dunwell) http://www.videokarma.org/showpost.p...5&postcount=10 Yours for 5 bucks, postage included. Cheers,
__________________
Brian USN RET 22YRS (Avionics/Cal) CET-Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit!
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#4
09-15-2015, 10:09 AM
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I've done this numerous times. But there's a caveat. It's always been on the standard layout with the damper in series with the B+ line going to the flyback.
I never did it on a pre-standardization layout where the damper is not in series. Your porthole is probably pre-standardization, so it might not work. Probably wouldn't hurt to try, though. Try a disc cap of around 47pf - 82pf @4KV. A quick check of the schematic will tell if it's a series layout or not. (EDIT.) Have you checked the G2 (screengrid) voltage on the H out tube? If it's low it'll cause reduced width and HV. Last edited by old_coot88; 09-15-2015 at 10:17 AM.
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#5
09-15-2015, 10:40 AM
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Since this is not normal operation for this set there must be an underlying problem, doing a "kludge" to get the width back might not be a good idea.
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#6
09-15-2015, 11:56 AM
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Little background on this set. I didn't do the resto, I got the chassis this way in a swap and put it into my table model porthole cabinet. Just about everything conceivable was replaced. Yoke, fly, resistors, caps, etc. All the correct parts. It's been looked at by a couple of the best TV minds I know, and nobody can puzzle this one out. It'll run for hours and be fine, basically just like this. Transformer is nice and cool as well.
This is a very weird chassis design. Half series string, half transformer. The top of the chassis is hot, but the sides aren't....they are insulated from the top by grommets and wafers. That said, I'll be okay with a "kludge" if it works 
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia."
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#7
09-15-2015, 12:41 PM
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The TV may be working just fine. The program you are watching may be in 16:9 format, which will show a picture with black bars at either side of the screen on any set designed for the old 4:3 aspect ratio. In this case, no amount of adjusting the width control will fill the screen. Another possibilty could be the horizontal output tube is so weak that, even with the width set at maximum, the picture will not fill the screen horizontally. The Zenith porthole TVs are late '40s-early fifties vintage, so it wouldn't surprise me if the tube (if original) is very weak, especially if the set's former owner(s) watched the TV a lot. There may be other problems, such as defective capacitors, but I'd check the tube first.
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Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten.
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#8
09-15-2015, 12:59 PM
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I see "jailbars" toward the left side which mean the flyback, as a tuned tank circuit, may be out of tune and ringing in a non-linear mode.
What is the chassis or model number? the TelAid might have something on this. It could be as simple as a bypass cap off the boost supply, or even a cap in the yoke, if used.
__________________
"When resistors increase in value, they're worthless" -Dave G
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#9
09-15-2015, 01:46 PM
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The ringing would indicate that something isn't right.
When the yoke was replaced were the resistors inside transferred or replaced? I used a Flyback from an RCA in a Zenith Porthole and got less ringing than that! I had to swap the resistors in the yoke to match the RCA design. Has a new 6BG6 and Damper tube been tried?
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#10
09-15-2015, 02:12 PM
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I can't really give much info, I'll see if I can get Al to chime in here.
Swapped the 19BG6, and it did make a difference....the right side wasn't as compressed as it was.
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia."
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#11
09-15-2015, 02:53 PM
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Hey gang. Thanks for chiming in to try and help get this porthole functioning better. I did a basic recap and replaced the flyback, yoke and any out of tolerance resistors. Old fly tested bad on two coils. New fly that was put in was a Merit HVO-11. Listed my chassis number (23G22) for an exact replacement. The yoke did not have any of the caps or resistors inside replaced (is an RCA yoke I believe), so any guidance and fix regarding this being a potential issue would be appreciated by Tim and I.
Now some info about the set. It is a 1950 Zenith Model G2346R (Graemere). Chassis number 23G22. The Zenith manual can be found on the ETF page here (page 37 of the PDF file is the correct schematic): http://www.earlytelevision.org/pdf/Z...anual_TV-5.pdf The SAMS that has this model number on it (G2346R) is NOT EVEN CLOSE. So I only used this original manual. This set has the 12LP4A all glass CRT too. Not the metal 12UP4. It is a part transformer / part series string set. The top plate of the chassis is hot. The top plate is riveted to the chassis sides with an insulator between the two. So sides of the chassis are not hot. Dial light runs off the B+ (red neon bulb). Some cooky stuff that I encountered for the first time. I was able to get a raster out of it, but it was weak, shrunken, with significant neck shadow, and had weak sound. Another member found a bad IF coil and when that was replaced, sound improved greatly and raster got way better. It seems to be compressed on the right side and has jailbars on the left side now, as someone mentioned. Would be great if we could be pointed in the correct direction to try a few things that might yield results. Thanks guys!!
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-Al
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#12
09-15-2015, 03:05 PM
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Quote:
In your package, along with the cookie, is a bag with some 4KV caps - 100, 130, 160 and 220pf - I was gonna send a PM about them but saw this. I remember we used a 100pf cap in some sets, but I couldn't remember the range of values, and it is probably 47-100pF, so I erred on the wrong (high)side. Hopefully all you need is the cookie. I see the flyback has been changed. FLy 52 and 53 (thordarson spec'd two flys for the PH's, not sure of Merit or Ram) are different animals, and it wouldn't be the first time someone (not you) changed a Flyback and used the wrong replacement. I have - on a Sony multi-system, and horizontal linearity was off - I adjusted to get it normal, and then had reduced width. So I called Sony, and they confirmed that I had the wrong fly, my mistake, and costly at that. Thankfully the set belonged to a good friend, so I didn't mind the lesson. On a side, the ETF museum has two flys for Zenith PH's listed on their website... Cheers,
__________________
Brian USN RET 22YRS (Avionics/Cal) CET-Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit!
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#13
09-15-2015, 03:08 PM
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Quote:
__________________
-Al
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#14
09-15-2015, 03:32 PM
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Quote:
haw haw haw 
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia."
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#15
09-16-2015, 07:15 AM
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Quote:
__________________
John
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Linear Mode
