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?

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,

PM sent! :D

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.

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.

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 ;)

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.

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.

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?

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.

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!!

Tim,

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,

Fly was replaced with a Merit HVO-11, which listed this chassis (23G22) in it's literature that was in the box with it as an exact replacement.

Looked normal while I was watching "Lockup"....

haw haw haw :D

Do you happen to have any more of these?

Unfortunately, no. The cookie places a cap of undetermined pf value across two pins of the damper - easy to do without it.

Cheers,

A small cap across the width coil will help also, but I agree with the others, there's something you're overlooking.

What was the original Zenith Fly? It'll start with an "S" - most of the Portholes used the Merit HVO-53, with some windings not used on some models.

Original flyback was Zenith S-16204. On your attachment it says replacement should be Merit HVO-53 (3). What does the "(3)" indicate? Assuming it is a reference to a footnote. What does the footnote say?

I cross referenced S-16204 to Merit HVO-11. When I got the part, the original paperwork was inside (got it from Moyer in PA). Below are two photos of that paperwork. Showing it is a HVO-11 and showing that it replaces S-16204 out of the 23G22 chassis. So not sure if one is wrong, or both are right, etc??? Interestingly, all the S-numbered Zenith flys on the HVO-11 paperwork cross to the HVO-53 on your paperwork.

Wonder if the HVO-11 was a no good replacement in these models and updated to the HVO-53 later??? Anyone have any insights?

Thx.

The (3) indicates that the installer should use the inclosed sheet for instructions. Merit apparently consolidated their flybacks for the PortHoles into one number, unlike Thordarson, who kept it between FLY 52 and 53.

With the Merit HVO-53, there are several sets of windings, and you use only the ones for your set.

Thordarson lists one flyback for your model number, and another flyback for the chassis:

For Chassis 23G22 (and 23G23), use a Fly 53 to replace a S-16204

For Model G2346R (and G2346RZ), use a Fly 52 to replace a S-16566

They show the early PH's as using the 52, and the later chassis using the 53.

Dunno why the discrepancy - anyone have a Zenith 23G22 parts list? Going by model is sketchy, it appears.

Cheers,

There is a parts list for the 23G22 chassis in the Zenith Manual I posted the link to earlier in this thread, isn't there? From the ETF site.

I have a HVO 11 in my 12 inch set and works perfect. The 11 fits under the chassis also. My 19 inch set its on top and it uses the 52 flyback they are very different.

Well, thanks to the cookie, I now have full width!!!

Picture's off center, but at least it's a full picture! :)

Cool! I am Portholio.......sorry Beavis.....:D

Hey cool!:music: That answers sumpthin' I've wondered about for very a long time-- whether or not the damper cap trick will work in a pre-standardization setup (i.e., where the damper is not directly in series with the B+ line to the flyback).

Forgive my ignorance but what two pins and why does that work?

Me thinks 3 and 5 - look at the picture - the bottom two pins (holes on the "cookie") are the two pins. I'm not sure, and also not sure of the capacitance, but 47-100pF has been suggested. I mailed it to Tim un-opened, so I didn't have a chance to measure it with my LC Meter. The cap is actually in the little tab that sticks up from the bottom.

Edit: 3 and 5 are the plate and cathode, so it makes sense.

Edit 2: Looking at the schematic, there is a 56pf cap in the yoke. As the yoke was replaced, it may not have the correct values in the yoke, making the cookie do the job of the missing/too low of value cap in the yoke....

http://www.videokarma.org/attachment...1&d=1439568364

Cheers,

I'll pull the back, yank the cookie, and measure it out tomorrow. There HAS to be more of these out there, somewhere.

All you really need is the cap, I am wondering if one is missing from the yoke of your set?

I have a 59 Sears 17" Portable that has a Cap with the leads just wrapped around the pins of the damper tube and hanging out the side, it looked factory to me but the set also had a fried flyback with severe distortion on one side of the screen, so maybe it was put there to try and compensate?

I was more asking for education. What does putting a cap across the cathode and plate of the damper accomplish (besides increasing width :scratch2:)?

More coupling of the horizontal sweep to the yoke, I'd imagine. Weak drive, a weak flyback, poor B+ regulation, improper impedance match/LC between yoke and flyback, variances in replacement yoke/flyback - you name it, it can produce reduced horizontal sweep. I remember one Emerson portable that had a shorted IF tube, and gave us no horizontal sweep, just a vertical line. The lack of sound and reduced B+ gave it away.

Just to expand a bit (pun:tongue:), adding the cap reduces the HV comensurately with the width increase. It also reduces cathode current a tad in the H out. tube. So it's a trade-off, no free lunch. Much higher than 100pf, the HV drops to where you start getting blooming.

If you recall, this was discussed near the end of the thread on your little Majestic 'Mighty Monarch' set. It had not quite enuff width to completely fill the screen. Using a damper cap was discussed. And since the set also had had issues with the HV rectifier arcing, it woulda benefited from slightly reduced HV also.
I didn't know then if the damper cap trick work on a pre-standardization setup, so it was never tried. But we now know it will work.

We usta keep 6KV disc ceramic caps of 47, 68, 82 and 100 pf for just this purpose. Also a 120, but never ended up using it that I recall.
4KV caps would be OK for just B&W sets, but 6KV covered color sets as well. (Certain Admiral color sets had horrendous issues with HV regulation and H out. tube overcurrent. It took some serious juggling of H out. sceengrid voltage and damper cap values to keep the the cathode current within reason.

You and Zeno, GURUs !! I lost my Dad (and his 50yrs experience in TV repair!) to cancer in 2011, but got new mentors between you and Zeno.

:ntwrthy: Thanks!

Riders Tv troubles and cures helps too. They are on line at etf I think. A lot of modifications and cures listed for various models. I know in the portholes some say put a 1 mfd across two connections on the fly or a .1 its been a while but it helped

It's not kludging, but corrective reengineering.



:smoke:

Some of us former techs got started on the bench in the late 70s when many of the tube Gurus were getting out of this busuiness, some bitter and treating it as a bad dream and not recalling much.

Electronic Technician/Dealer magazine was helpful to take us back to the design stage, allowing such improvements. It became very important with keeping the HV in check with Solid State Sweep.

Just imagine the pressure to get these designs into showrooms, before all the "burn-in" testing is done.

Thanks Old Coot!