I found this for sale here in Spain, just a 14-hour ferry trip away. If I'm not mistaken this is one of the last all-tube color chassis, definitely before the 4-tube hybrid era.

It's particularly interesting to me because these weren't built or sold here and it may be the only chance I have to get my hands on a Zenith color set with tubes in it.

What say you, VK?

https://cdn.wallapop.com/images/10420/32/xs/__/c10420p186334222/i416435792.jpg?pictureSize=W640

:thmbsp: I like it , and considering the rarity of such sets in Spain if a 14 hour ferry trip isn't enough to scare you off , by all means , go for it !!!!

:scratch2: Kinda puts into perspective what folks in other parts of the world have to do in order to secure such a set , here I know of folks who wouldn't take a 4 hour trip , much less a 14 hour trip !

:D Hopefully the 14 hours is round trip , as in 7 hours each way ?

I found this for sale here in Spain, just a 14-hour ferry trip away. If I'm not mistaken this is one of the last all-tube color chassis, definitely before the 4-tube hybrid era.

It's particularly interesting to me because these weren't built or sold here and it may be the only chance I have to get my hands on a Zenith color set with tubes in it.

What say you, VK?

https://cdn.wallapop.com/images/10420/32/xs/__/c10420p186334222/i416435792.jpg?pictureSize=W640
It looks like a 12A12C52, a 1970 model year. One of my favorites, a great performer. Hybrid chassis, 12 tubes in sweep circuits, tuner and audio.

It looks like a 12A12C52, a 1970 model year. One of my favorites, a great performer. Hybrid chassis, 12 tubes in sweep circuits, tuner and audio.

I've got a very similar 1971 model (cabinet was called the Boyden) with the 12B13C52 chassis. Same number of tubes. The chassis is ~half discrete transistor solid state, with the chroma demod being a DIP IC on a lone duramodule board similar to those used in their SS sets. Very good sets.

This set is missing the hue knob and it's hole so my guess is that it is an export PAL model.

I've got a very similar 1971 model (cabinet was called the Boyden) with the 12B13C52 chassis. Same number of tubes. The chassis is ~half discrete transistor solid state, with the chroma demod being a DIP IC on a lone duramodule board similar to those used in their SS sets. Very good sets.

This set is missing the hue knob and it's hole so my guess is that it is an export PAL model.
I knew that the control panel looked a little different.
I wonder if the sets came from the factory as a PAL version. The set is old enough that the PAL system was around for awhile.

It looks like the hole for the hue knob shaft was never punched in the face panel so I'd be inclined to think it is factory.

:scratch2: Kinda puts into perspective what folks in other parts of the world have to do in order to secure such a set , here I know of folks who wouldn't take a 4 hour trip , much less a 14 hour trip !

:D Hopefully the 14 hours is round trip , as in 7 hours each way ?
Being an obsessive crackpot I'll do anything in my power to secure a set I want. For instance, I pushed one of my own sets most of the way home on a trolley in the snow, about six kilometers before I was offered a ride the rest of the way which wasn't much farther.

Round trip or one way, that's what I've been wondering since I saw the original post.

I found this for sale here in Spain, just a 14-hour ferry trip away. If I'm not mistaken this is one of the last all-tube color chassis, definitely before the 4-tube hybrid era.

It's particularly interesting to me because these weren't built or sold here and it may be the only chance I have to get my hands on a Zenith color set with tubes in it.

What say you, VK?

https://cdn.wallapop.com/images/10420/32/xs/__/c10420p186334222/i416435792.jpg?pictureSize=W640

Looks like a 23 inch Zenith Chromacolor, circa 1970/1971. We had almost the same exact model, it was called the Boyden IIRC.

Thanks everyone for the info! My grandparents had one that looked just like this, so it had a nostalgia pang added to the rarity factor for me.

Yeah, 7 hours each way on a ferry, I don't think anyone would ship it so I'll have to take a car ferry out to Mallorca to pick it up.

Very interesting about the possibility of it being a PAL model. It's entirely plausible, as Zeniths were built under license by a company called Televasa in Barcelona toward the end of the dictatorship, but I haven't been able to get much info on dates or models produced - this is the only color Zenith I've seen here.

I'm going to go for it.

ETA: this is the only Zenith of this era I have seen that didn't have a green halo. I wonder if the CRT is different as well? I know the other sets made under license in Spain used home-grown tubes (complete with weird-o European numbers) to avoid a hefty import duty.

Hello. I have a couple of sets assembled by Telerasa of Spain. I must say they seem original Zenith tvs with the exception they have different cabinets (of lower quality) and back panels. All the parts inside, included picture tube, are genuine Zenith products so I guess there was a production line made for export in Europe. One of mine also has the telephone module just like many of the original system3. I had exactly the tv in the picture but mine was made in USA and was modified to work here in Italy. I seem to remember the picture tube was a Chromacolor type, the one with black matrix dot screen. I would love to find my infancy Zenith, a portable with 15y6c15 chassis but this is another story.

Zenith sold "kits" to many foreign countries. They pop up
in some strange places. It seems consoles had a local cabinet.
Portables looked slightly different than ours. All this was
done to get around taxes. If it wernt for taxes they probably
would have built them here.
Sets built in Europe are rare here. I have only seen a few Grundig
multi-modes brought back by servicemen. Most they had were
Jap or ROK sets, Sanyo the most often seen. As far as I know
no US company built multi modes for retail sales.

73 Zeno:smoke:
LFOD !

I'm waiting for this guy to get back to me so we can set a time to pick it up.

There are several American brands here (I started a thread a couple months back with photos), all of which seem to be either built here or made specifically for export - lots of bug-eyed picture tubes, etc., and the ugliest Sylvanias you ever did see.

Four years and one pandemic later, I finally managed to get this set. :banana: Actually, not this set, but another one just like it. It's been sitting for a while because color sets still intimidate me. But it's time. Cabinet's in bad shape, CRT tests great. Let's get it going; I have a place to put it where it will get some occasional use.

https://i.imgur.com/N0Cpysxl.jpeg

The 9B23P70 chassis seems to be mostly identical to the 12A/B13/14 hybrid American sets, with the odd empty hole in the chassis where the color tubes should be. The 6JD6 and 6EJ7 are missing, along with the 6GH8. There's a second DuraModule underneath a shield where the 6GH8 would otherwise be that has a couple of DIP ICs on it. I'm using the Sams 1157-2 as a reference, though I am trying to track down someone who may have the actual factory schematic.

https://i.imgur.com/rmy8ffSl.jpeg

I already brought the set up on a variac, it produced a picture for about 1 second along with some loud popping from the HV area, and then the screen went dark. Sweep/HV tubes were removed and tested and seemed to be OK. I put them back in the set, powered it on again, but no brief picture and no high voltage, confirmed with a HV probe.

I did some preliminary checks and determined that the Horizontal section is working correctly up to the flyback, voltages on the HO tube are correct, I have about 330V of drive on the grid and it looks right. My first thought, given the brief flash of picture, was that the HV was too high and a failsafe had shut it off. Now that I have the Sams I understand that's not how it works. I did voltage checks around the damper and HV regulator and everything on this side of the flyback seems to be off: both the grid and cathode of the 6HV5 have less than 100 volts, and I don't think there is any boost voltage. I don't have a meter that can read that high and my high voltage probe doesn't even wiggle when I probe the boost source. I also notice that a few of the resistors in the horiz and HV circuit have been cut and tacked back in, and upon opening the HV cage I found the HV rectifier socket had been unscrewed from its mounting though all the wires are attached, the tube is in place, and plate cap is connected. So I'm not the first person wondering why there is no HV.

And I've kind of hit a wall. I don't understand how this part of the HV section works, so I'm not sure where I need to go from here. I've been doing a lot of searching online for descriptions or explanations and mostly I'm just turning up other threads here talking about VDRs, and a mention that the grid voltage on the HV regulator "comes from the horiz oscillator", which I really don't understand.

I would like to understand how this part of the set should work so that I can troubleshoot it, can anyone point me in the right direction? Is there a Zenith service manual that gives some detail?

Thanks everyone.

This is an interesting set and I look forward to reading more about it in the future.

A few notes. You can measure the 875V boost rail (that's what the Sam's for my 12B13C52 claims it is) with a 600V meter. The highest regular B+ rail is 405V (again working off my Sam's)...If that 405V rail is a constant voltage with respect to ground write that voltage down then measure the difference between the 405V rail and boost (meter - on 405, meter + on boost), then add the measurement from the 405 rail to the boost difference measurement to get actual boost voltage...It's kooky l, but it works in a pinch...Ask me how I know.

If the yoke has made in Holland and a phenolic wafer facing the screen under the rear plastic cover it could be a shorted yoke...I just dealt with one of those yokes on a 16" portable (it used electrically the same yoke and connector as my console) it would warm up and short and after 15min slowly kill the HV...the 15 minute warmup time (as well as H out Grid drive dropping with boost as a red herring) made it a PITA to troubleshoot but I fixed it after 2 days...I was lucky to have one older Zenith yoke that was all plastic (no phenolic) to swap in as a replacement.

IIRC the pulse regulator samples the boost voltage ( I think it does so at a specific point in sweep gated by the damper) and adjusts the H output tube bias to reduce or increase HV. Basically the Boost voltage is a VERY good indicator of the load on the flyback. Assuming the HV system is working properly the only thing loading the flyback that will change the amount of loading is the CRT beam current load on the HV so if you adjust horizontal to vary energy supplied to the flyback with a feedback loop that holds boost constant, then you can effectively hold HV constant too. I may be oversimplifying it a bit as it's been ages since I read about it, and it's rare that I need to troubleshoot one of those circuits.

Pretty much all TVs even unregulated monochrome sets get H output grid bias voltage from the oscillator. Basically the AC signal gets rectified by the grid/cathode and that creates the bias...It works similarly to grid leak detector triodes in 20s radios if you are familiar with that.

If this were my set I would put a meeter on the boost use the plate drive of my B&K 1077 to drive the flyback then unplug the yoke and see if boost improves...That would sniff out a bad yoke fast.

Thanks Tom!

Funny you should mention the 1077; I pulled it out last week planning to use it for just the purpose you mention and unfortunately it's got a bad yoke. I suppose I could put it back together and use it just to try to generate H sweep on the Zenith, but it seems like it's probably not worth the hassle if I'm not sure what I'm getting out of there. I wonder if I could borrow the H plate drive from a working TV like a B&W Zenith from the same era.

I think my next step will be to put the HV rectifier socket back in its place, test the boost (great suggestion) and then remove the chassis to test all of the passive components in the section - it's the only part you really can't easily get to when it's stood on its head. Both your explanation of the HO grid bias makes sense, and so does using the boost as a reference for the regulator. Thanks again.

You're welcome.
A few thoughts. You can use the horizontal output of one set to drive another (the 1077 is basically that only it has a second output tube dedicated to the task) as long as there's no hot chassis action going on and you ground the chassis together. A monochrome set will be a little weak to drive a color to normal levels, but honestly so is a 1077 (boost and sweep width won't be full on).

Monochrome yokes are fairly universal (neck size and deflection can be issues) If you have anything that fits over the 1077 neck it might work.

Wow nice set

This is a beyond-interesting thread for sure, I hope you find a schematic. Design changes that are fascinating, starting with the power supply.

The VDR in the 6HV5 circuit should be replaced if you can. That one item is holding me up on all my post-66 tube Zenith color sets, to make sure HV won't go too high. The 66 and earlier Zeniths used a 6BK4 shunt regulator tube with no VDR.

I still have the 12B14C52 my parents bought and the first time I saw the picture of this import model without a Hue knob, I was looking daily for updates on this post. Thank you Alan!

Glad you're enjoying it, Dave! I'll fill in a bit more information you and others might find interesting. Getting back into TVs over here has been a fascinating experience. So much to learn about the way things worked and were built in Europe that I had never been exposed to, and the surprisingly big role some American companies played in the market here. I think the American stuff was likely political in nature. Spain was still a dictatorship until 1975, and I have a feeling that their relative pariah status enabled the US government to help out by setting up American companies here. I don't know for sure that's the case, and the few conversations I've tried to have aren't really something people want to discuss a whole lot.

Anyway.

So, neither my Zenith, nor the others you have seen, were export models. They were built in a Zenith factory right here in Barcelona.
https://d129a85b0t6mus.cloudfront.net/public/DigitalAsset/a7367e4909af5f18ab9b46042eac1667/a7367e4909af5f18ab9b46042eac1667/full/large/0/default.jpg
https://i.imgur.com/8Arfakbl.jpeg

Zenith Radio Corporation set up a joint venture here, bankrolled a factory, and started building sets based on American models with a mix of imported American and European-sourced parts. Pre color, the sets were nearly identical to their US counterparts. I have a couple of boat anchor 12" B&W sets that, aside from an autoformer and switch to select the mains voltage, have identical chassis in every way that I can see to an American set. I have the Sams for a 13M15 chassis, mine is a 13X15, and all the parts - tubes, electrolytics, are American, and all the values of components in the sweep circuits, etc., are unchanged. The text on the back is in Spanish, saying it was built here, and the VHF knob has those dorky European channels like E on it.
https://i.imgur.com/c279uWGl.jpeg



I also have a Philco set based on the American 14J41 ("The Townhouse") chassis. As opposed to setting up their own factory, Philco contracted with a local company to produce sets based on American designs using a mix of parts. My set has all original markings - chassis number, cabinet back with the notice in English about complying with FCC regulations, everything, but the luxury tax stamp on the chassis indicates it was built by Iberia Radio, who sold sets under their own brand and produced for a bunch of others - I have seen Emerson and Westinghouse sets built by them using European designs. My Philco has a different power transformer than the American one, and the power supply has been heavily adapted to work here. The chassis itself, PCBs, and tubes are all identical to the Sams, but almost all the passive components were locally sourced, with Bianchi electrolytics that are all still good. Lots of bodges, capacitors tacked under the PCB, etc., and the tuners are completely different than what's in the Sams. I haven't ever seen a Zenith ad in Spain, but Philco were ALL OVER IT, with heavy print campaigns and they even got Miss America to come over here and pose for a picture with one of their fancy Yankee TV sets. They leaned into the fact that they produced (I think) a camera tube used on one of the moon missions to claim that the US government trusted them for the new era of Philco space exploration. No comment.
https://i.imgur.com/M0xnXzw.jpg

I have tons of pictures of the insides of these weird-o sets if anyone is interested, along with a GE built by Philips.

Back to the Zenith at hand. I'm taking the yoke off of an old Philips I have and will see if I can get the 1077 going. That's the plan for today.

Hey made some progress today. I put the HV rectifier back in its place, and removed, cleaned pins, sockets, and re-seated the sweep tubes, and powered it up again, with a meter across C146. It rose to an indicated 460V (so adding the 400V B+, that would give 860V, just about the 875V Boost in the Sams) and I heard the HV come up for about 2 seconds, then the Boost started dropping down to an indicated 160V, again referenced to B+, where it pretty much stayed for a few minutes.

Click to embiggen:
https://i.imgur.com/biQbjyal.png (https://i.imgur.com/biQbjya.png)

I repeated the test a couple of times more and the HV never returned, and the Boost never rose above that indicated 160V. I'm going to let the set cool down completely and try again.

This is the behavior I saw on first power-up, and so I think the completely dead HV was an anomaly caused by removing the tubes and moving things around. Now that I know it can make HV I don't have to hassle with putting a yoke in my 1077, and can hopefully go on to troubleshoot the actual problem.

Another thing I noticed: the 400V B+ is low, about 360V. This 400V source goes only to the Boost filter, and is derived from the main B+ that goes through the vertical centering control. I'm not sure why that is, that control is also connected inline with the yoke and it seems to me there would be an awful lot of noise on that 400V line, no? Anyway unless the source of the 400V is pertinent to the problem at hand I'd prefer not to worry about the why for right now. I'm going to connect another meter to the 400V source at the cold power-up and see if it's normal before the boost starts dropping, that may help me figure out if this is due to excessive current draw or something else.

This set has two varistors, one off the grid of the HO tube and the other between Boost and the grid of the HV reg. Is it possible one of these could develop a thermal intermittent causing...something? My theory right now is that the dropping boost is a symptom of whatever is really going on, and that low B+ is probably a clue. I'm reading the articles I've found in old Photofact Reporters about this circuit but still don't have my head around it.

Anyway thanks again for the all the suggestions, help and encouragement. As a thank you, here is a picture of the PAL DuraModule where the 6GH8 ought to be. I'm wondering if this is "real" PAL or some kind of reverse-engineered faux-PAL.
https://i.imgur.com/wnBBNBWl.jpeg

Interesting stuff. A few notes:
Modelo B4519W KT Following US convention
B is model year "B line"
45 means 23" US size. ( 19" is 40, 25" is 47 )
19 is a consecutive ## the higher the better.
W is walnut ( X is white, M maple, P pecan etc )
KT must mean kit, never seen that.
Chassis numbering UP TO B line. example 4B25Z19
4 is tube count ( not inc CRT)
B is B line
The rest I do not know
Set is one step below the 4 tube hybrid that came out the same year.
Color module takes the place of our 9-27 but looks different. If your
manual shows a 6GH8 its probably the wrong one.

Check the ground lugs for the terminal strips. They can crack & cause ints.
Check the damper & HV reg against the tube chart. You need the right
pair for it to regulate. I dont remember why.

73 Zeno:smoke:
LFOD !

Some additional notes to Zeno's. I believe the hybrid chassis numbers up to B line included both tube count and transistor count. For example my 15Y6C15 IIRC has 15 tubes and 6 transistors.

Zenith didn't want the set to work without the HV regulator installed so they wired the damper and reg heaters in series. However there were 2 different heater current HV regs and 2 different heater current dampers....If you didn't use a pair with matched heater current one tube wouldn't warm up properly and the other would have excessive heater voltage...I don't know how it effected the HV but it obviously wouldn't be good.

Your boost is actually 820 since the 400V rail is only measuring 360V.

IIRC it's possible to run one of these sets without the HV regulator if you use clip leads to connect only the heater of the regulator. HV will be as high as it can be that way but if you need a go/no-go on the flyback that is a way to get it.
I have a 20CC50 that years ago I wanted to fix but didn't have the IIRC one and only HV reg it needed. I think I briefly ran it like that to make sure the fly was OK, then I figured out I could add or swap a wire for a cathode, plate or grid to make a 6HV5 work in it.

Well, my set has 11 tubes so who knows! I've also found a few other discrepancies, the Sams shows a 6Z10 for audio detector and audio output, but my set just has a 6BQ5. Dunno what's doing the detecting...

I have found a guy here who thinks he has the original service manual for that set, he's going to look for it this weekend.

Meanwhile, I did some more tests. It's not just the 400V that's low, it's all the B+, including the main 405V line. With a cold startup it goes up to about 400V and then drops quickly to around 350V once the various circuits start working.

So in the meantime my big question: is the low B+ a symptom of the problem with the HV? Or is the HV a symptom of a problem with the B+? Or are they likely two unrelated problems and that low B+ may not have anything to do with the lack of HV? Which to tackle first?

I've checked that none of the filters are getting hot, and there's a big 18W dropping resistor in the power supply that isn't getting any hotter than I would expect it to.

Both systems are capable of effecting the performance of each other.

I would check the horizontal output cathode current. If it is excessive it could be lugging down the B+.... Likewise if the H output tube or damper is removed and the horizontal output stops drawing B+ current entirely then the B+ should increase beyond it's nominal design voltage.

The Horizontal output is typically the largest current draw on the B+ so B+ won't be normal if H output current isn't reasonably close to normal.

HV can also be reduced (though you should still get raster) by low B+. If you ever run a set on a Variac and observe reduced HV and usually either blooming or shrunken raster you can see that in action.

I tracked down the schematic! It's in the Spanish equivalent of Riders, looks like. Anyway the book is on its way. The chassis number doesn't match but the guys on the local forum assure me this is it, in fact it's all the color chassis Zenith made here.


https://cdn.wallapop.com/images/10420/9n/6l/__/c10420p583134011/i1793987384.jpg?pictureSize=W640

Regardless I have some time today I'm going to dedicate to tracking down what Tom said above.

As an aside, the GEE logo was classic GE minimal effort

As an aside to that aside, GEE was at least partly owned by the state back then.

The choice of color system was a pretty big deal politically because it allowed the main players, USA, Germany, France, a degree of influence over technical policy in the countries that chose their system. It was almost always a political choice rather than a technical one.

Spain had decided on SECAM as their color system in the mid 1960s after a few years of trialing PAL, SECAM and NTSC. Once the decision had been announced, nothing happened and the people were asking why there was none of this promised color on the single (state-controlled) channel that existed at the time.

After three years of non-action, the Ministry of Culture said oops our bad, we meant PAL. At the same time, but totally unrelated, the German government handed over 200 million Deutsch Marks to the Spanish government as a loan (wink wink). The French were livid. As a consolation prize, Spain "gave" GEE to Thomson. All the press I can find from the era just say things like "gave" or that they "received" GEE. It's not super clear if it was just a gift or they paid something for it. Anyway, French Thomson wound up with half-ish-Spanish GEE, who didn't make anything* and had been selling TV sets based on a Dutch design built in a factory in Barcelona, as the consolation prize after Spain chose a German color system. Europe!

And yeah, that logo is not at all surprising coming from GE and Spain.



*Evidently they made industrial motors for trains, and still do, but no consumer electronics, those were all farmed out to the lowest bidder.

As an aside to that aside, GEE was at least partly owned by the state back then.

The choice of color system was a pretty big deal politically because it allowed the main players, USA, Germany, France, a degree of influence over technical policy in the countries that chose their system. It was almost always a political choice rather than a technical one.

Spain had decided on SECAM as their color system in the mid 1960s after a few years of trialing PAL, SECAM and NTSC. Once the decision had been announced, nothing happened and the people were asking why there was none of this promised color on the single (state-controlled) channel that existed at the time.

After three years of non-action, the Ministry of Culture said oops our bad, we meant PAL. At the same time, but totally unrelated, the German government handed over 200 million Deutsch Marks to the Spanish government as a loan (wink wink). The French were livid. As a consolation prize, Spain "gave" GEE to Thomson. All the press I can find from the era just say things like "gave" or that they "received" GEE. It's not super clear if it was just a gift or they paid something for it. Anyway, French Thomson wound up with half-ish-Spanish GEE, who didn't make anything* and had been selling TV sets based on a Dutch design built in a factory in Barcelona, as the consolation prize after Spain chose a German color system. Europe!

And yeah, that logo is not at all surprising coming from GE and Spain.



*Evidently they made industrial motors for trains, and still do, but no consumer electronics, those were all farmed out to the lowest bidder.
Fascinating. I have to wonder if this helped contribute to Thompson buying American GE/RCAs consumer electronics division in the late 80s early 90s...We already have a foot in the door of owning them let's just buy whole shebang since twiddle dee is selling his company piece meal.

Europe seems to have been almost as dysfunctional as the US was back then! Interestingly, Spain trialed French nuclear technology (CO2 cooling, already obsolete) and US designs (including the only one loop PWR Westinghouse ever sold). I don’t know if Westinghouse had any other involvement over there (they sure did in France, Framatome was born out of Westinghouse’s four loop reactor)

Spanish electric locomotives are 3,000 volt DC power. GE in the US (and South America) was a big proponent of 3,000 volt power. A few Spanish electrics in the early days were built by Alco in the US, who had close ties to GE.

None of this has much to do with TV, but might be interesting to someone…

Oh, I think most history is interesting! I have wondered about the Thomson/GE connection too...

Funnily enough, Westinghouse operated here in the 60s and 70s selling the exact same rebadged Philips/Miniwatt-made TVs that GEE did. I have one of the GEEs but the Westinghouse are harder to come by.

Ladies and gentlemen, BEHOLD

The (slightly blurry) schematic for a PAL Zenith. It has some important differences from the Sams I've been using as a reference. I'll do a clearer scan later today.

Crossing my fingers I'll be able to get this going.

That's a unique slice of time, with tubes, transistors, and analog bipolar ICs.
Very nice!

Here's a cleaned up and more legible schematic. The entire sweep and HV section is different than what I've seen in the Sams, including the damper and HV Regulator tubes, which had the numbers illegible in the set. B+ is lower than the Sams version, and it's exactly what I have measured, so hopefully things will make more sense now :) . I'm going to start again using Tom's suggestions and the new schematic and values and see where that leads.

Zenith B4519WKT - 1 (PS, Sweep, IF) (https://www.dropbox.com/s/d697iy2ukchioco/Zenith%20B4519WKT%20-%201%20%28PS%2C%20Sweep%2C%20IF%29.pdf?dl=0)

Zenith B4519WKT - 2 (Video, Chroma, Sound) (https://www.dropbox.com/s/akhdtc29qcpn3s2/Zenith%20B4519WKT%20-%202%20%28Video%2C%20Chroma%2C%20Sound%29.pdf?dl=0 )

OK, I could use a little more help here...

B+ is low across the board. Main B+ is supposed to be 390V, I have 350V even with the HO tube removed. I only have 355V before the choke. Adding the HO tube makes it drop by a couple of volts. So there is either something wrong with the B+ supply or there is something dragging it down. The filter cans don't get warm even after 15 minutes, R399 that big dropper resistor is hot but not more than I would expect for a 15W resistor. And even though the B+ is low, if everything else were working, I should still have HV, right?

Moving on to the horiz/HV section: the HO output tube is hot, but according to two different meters I put in series with that cathode fuse it's not drawing any current. Well, one says 0 and the other says 1mA. Fuse is good. There is drive on the grid, measured -48V and about 300V drive from the 6U10 that looks like the Sams picture. However! The screen is quite high, at 160V. Now here is where I could use some help. Please disabuse me of my misconceptions and half-understood leaps of logic:

1. If the B+ is low, and the screen, which is fed from the 390V B+ through a couple of resistors, is high, that would indicate that the tube isn't conducting, right?

2. If the cathode current measures 0, that would also indicate that the tube isn't conducting, right again?

3. Where does the HO tube get its plate voltage? The only path I can find is the 390V on the secondary of the vertical output transformer, that goes through the vertical centering control and makes its way to the plate of the damper. It would follow that the damper is conducting from plate to cathode, over to the flyback, and then to the plate of the 6LB6. Am I right? That seems...convoluted. It must be for a good reason.

4. I am starting to suspect there might not be plate voltage on the horizontal output tube. Except! When the damper is in the set, I can hear the vertical output transformer thumping away. When the damper is removed, no more vertical. Since the vertical output tube gets its plate voltage from the selfsame 390V that's on the plate of damper, that means the VO tube isn't directly dependent upon Boost being present. However! The vert osc gets its plate voltage from Boost and nowhere else, so this must mean that there is Boost present, which must mean that the HO tube is indeed conducting, or there wouldn't be boost present. Which means my plate voltage theory is wrong. But I want to verify before I just stick a probe on there and vaporize a perfectly good $15 DMM.

OR, is there enough of that 390V dribbling through the damper circuit to run the vert oscillator? In which case it would be safe to measure the plate on the HO tube and get a clue where to go next.

I cannot figure out for the life of me where the 870V Boost is coming from. I have re-read both Grob and Gulati on this subject but I'm getting lost.

Thanks everyone for your guidance.

Question: who's got two thumbs, enough knowledge to be dangerous, and a Zenith with high voltage?

Answer: 👍 this guy 👍

https://i.imgur.com/f6uIIEYl.jpeg

'Twas the HV regulator socket, had come unsoldered from the chassis and ungrounded several things. Tomorrow I'll clean the tuner, send it a real signal, and see if it makes any color. Very exciting. thanks again for the help everyone.

Great news there.