Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Rectangular Screen Tube Televisions

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 07-21-2018, 08:06 AM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
Help me identify this Zenith?

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?

Reply With Quote
  #2  
Old 07-21-2018, 09:19 AM
init4fun's Avatar
init4fun init4fun is offline
VideoKarma Member
 
Join Date: Mar 2011
Posts: 1,169
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 !!!!

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 !

Hopefully the 14 hours is round trip , as in 7 hours each way ?
Reply With Quote
  #3  
Old 07-21-2018, 09:44 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by AlanInSitges View 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?

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.
Reply With Quote
  #4  
Old 07-21-2018, 10:25 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
Quote:
Originally Posted by dieseljeep View Post
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.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #5  
Old 07-21-2018, 12:40 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 7,562
Quote:
Originally Posted by Electronic M View Post
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.
Reply With Quote
Audiokarma
  #6  
Old 07-21-2018, 02:31 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
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.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #7  
Old 07-21-2018, 05:57 PM
Jon A.'s Avatar
Jon A. Jon A. is offline
Don't mess with Esther.
 
Join Date: Jun 2013
Location: Canada
Posts: 4,267
Quote:
Originally Posted by init4fun View Post
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 !

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.
Reply With Quote
  #8  
Old 07-21-2018, 08:24 PM
NowhereMan 1966's Avatar
NowhereMan 1966 NowhereMan 1966 is offline
Slave to 1 Cat
 
Join Date: Dec 2004
Location: Tiltonsville, OH
Posts: 884
Quote:
Originally Posted by AlanInSitges View 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?

Looks like a 23 inch Zenith Chromacolor, circa 1970/1971. We had almost the same exact model, it was called the Boyden IIRC.
__________________
Mom (1938 - 2013) - RIP, I miss you
Spunky, (1999 - 2016) - RIP, pretty girl!
Rascal, (2007 - 2021) RIP, miss you very much
Reply With Quote
  #9  
Old 07-22-2018, 07:01 AM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
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.
Reply With Quote
  #10  
Old 07-25-2018, 11:41 AM
tritwi's Avatar
tritwi tritwi is offline
zenith mad
 
Join Date: Sep 2005
Location: Florence (Italy)
Posts: 125
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.
Reply With Quote
Audiokarma
  #11  
Old 07-26-2018, 08:37 AM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
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
LFOD !
Reply With Quote
  #12  
Old 07-27-2018, 05:20 AM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
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.
Reply With Quote
  #13  
Old 04-11-2022, 04:20 PM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
Four years and one pandemic later, I finally managed to get this set. 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.



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.



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.
Reply With Quote
  #14  
Old 04-11-2022, 06:10 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
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.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Last edited by Electronic M; 04-11-2022 at 06:16 PM.
Reply With Quote
  #15  
Old 04-12-2022, 09:55 AM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
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.
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:12 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.