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 Post subject: First Project, 1940 Zenith 15S495
PostPosted: Mar Tue 08, 2011 10:55 am 
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Joined: Mar Sun 06, 2011 11:41 pm
Posts: 6
Location: Bellingham, WA
(edited to nix Giant Images)

I've been on the hunt for an affordable project to get my feet wet in the world of old radios. Came across this console on CL and managed to get it home before DW could change her mind.

Really rough cabinet. I would guess that someone had a leaky aquarium or potted plants on top. It is badly delaminated and missing a big chunk.

First exam of the chassis in the cabinet and I felt certain that no one had messed with it before. Totally rotted out rubber wiring, including the patched, spliced and taped up power cord. If anyone had tried to plug it it, it would have instantly shorted in half a dozen places and maybe shocked them for good measure.

When I pulled it out, though, I found that someone had replaced the 10/10 electrolytic located dead center on top of the chassis and also the big 12 mf electro's for the power supply. Not sure how old these Spraques are, but I can't believe it was long enough ago that the wiring was any good. Perhaps an aborted repair attempt?

Looking at the schematic, I'm pretty sure that the twinned together cans were wired incorrectly. First off, they use a pair of 8 mf caps instead of two 12 mf. That seems like a big jump to me. Then they twisted both ends together to make one big 16 mf, when I think it should have been each cap coming off opposite legs of that coil mounted to the chassis (which also looks suspiciously new).

I got the schematic and parts list from Steve Johnson and have it all printed out, but looking into the guts of this beast makes my eyes swim. I'll need to spend some time sorting out this point to point wiring thing. Right now, it is hard to make the leap from diagram to reality and have it make sense.

From what I have read so far, I figure it will need a complete recap and replacement of the bad wires just as a start. That alone will take me awhile!

Any tips on making sense of this rats nest and making my shopping list?

One other thing that puzzles me - are the brightly colored little "pneumo tubes" actually resistors? I had at first thought they were a variety of paper capacitor, but there are way too many of them for that! If they are resistors, how do I decipher their original values?

Thanks!

Ben


Last edited by triple.ratrider on Mar Thu 10, 2011 5:53 am, edited 1 time in total.

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 Post subject:
PostPosted: Mar Tue 08, 2011 12:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1944
Location: OOLTEWAH,TN.
Ben the resistors are body = 1st figure end= 2nd figure dot=multiplier you will need belts do it right and get them from www.Adamsradio.com NOT O rings i have restored over 40 big Zenith's i have never used O rings i have removed a lot of them take your time in restoreing your set it's a very nice set i would put a fuse in the A.C. line also good luck SMITHY


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 Post subject:
PostPosted: Mar Tue 08, 2011 1:25 pm 
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Joined: Mar Sat 06, 2010 3:37 am
Posts: 591
Location: Walton Hills (near Cleveland)
Hey there it is! Glad you bought it. This is a great site and many helpful people here.

Check out Phil's site and this link on recapping:

http://www.antiqueradio.org/recap.htm

I have to admit I am jealous that you got a 15 tube Zenith! They are hard to come by, 1940 had the least amount made.

Lenny


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 Post subject:
PostPosted: Mar Tue 08, 2011 1:53 pm 
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Joined: May Sat 22, 2010 4:42 pm
Posts: 2975
Any wires that have woven insulation on them probably do not need to be replaced-- the woven stuff will hold the somewhat crumbly rubber in place.

I would replace the crumbly wires going to the tube top caps, and any wires carrying line voltage, but not much else of the wiring unless you actually can see crumbling and bare spots.

The yellow caps probably need replacing again. The values are probably okay as the tolerance of the capacitors is like -50 to +200%, and the circuit can tolerate wide swings too. The other side of the filter choke probably has the other capacitor, the yellow one by the speaker plug, as its filter cap.

Just take it slow, one capacitor at a time. I'd turn it up slowly with a variac, then replace the caps going to the output tube grids, then the filter caps, then slowly the rest of the capacitors.


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 Post subject:
PostPosted: Mar Tue 08, 2011 6:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2726
Location: McPherson, Kansas
That is one BIG radio *pic*

And a big one to start learning on. Good luck.


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 Post subject:
PostPosted: Mar Tue 08, 2011 7:07 pm 
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Joined: Mar Sun 06, 2011 11:41 pm
Posts: 6
Location: Bellingham, WA
Thanks guys! I'm trying to read as much as I can find as I go into this, so links and tips are much appreciated!

It's good to know that I won't have to replace every bit of wire. Funny thing, it isn't quite as daunting when I look at the picture I posted.

If I were to knock together a Dim Bulb Tester, will that suffice in place of a proper variac to get me started? I'm not sure where I'd even look to find one around here or what good used variac should cost.

Ben


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 Post subject:
PostPosted: Mar Tue 08, 2011 10:16 pm 
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Joined: Aug Tue 24, 2010 8:56 pm
Posts: 3466
Location: Florida
Don't do the complete recap all in one shot; instead, replace the filter (electrolytics) first, along with any wires in danger of shorting; at that point, you can test it with a dim bulb tester.

You can get a variac on ebay.


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 Post subject:
PostPosted: Mar Tue 08, 2011 10:19 pm 
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Location: New York USA
The dim bulb tester is even safer than a Variac, as the bulb limits current, a short in the radio won't damage anything, just makes the bulb get brighter.
Don


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 Post subject:
PostPosted: Mar Tue 08, 2011 10:45 pm 
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Joined: Feb Wed 02, 2011 5:59 am
Posts: 875
Location: Newton NJ
Nice radio to get started on! Will be a really good player when done. I have a similar Zenith that can really belt out music. First thing I would do, check your tubes. Not only as to good and bad, but as to placed in the sockets they belong. Next, get the lay of the chassis. Find your audio output tubes, your rectifiers, and so on. Like others have said, don't do a complete recap right off the bat. Definitely replace the rotten wiring, one piece at a time. I usually remove one wire, measure a new one to fit and install. You can take a marker and dot the terminal where you take the wire off. When you solder back the new wire, chances are the dot will vanish too.

Start with the power supply. Replace filters with as close to correct values as you can. 8uf can be replaced with 10uf, 4 with a 4.7 and so on. Check component wiring vs schematic, before and after you replace it, especially if someone else was in there. Bring power supply up slowly, variac or the dim bulb route works great. Power supply and Audio out ckts are the hardest working ckts and will usually need most attention. Do the audio amp next, and then work your way back to the rf amp and osc etc. Take lots of pictures before you dismantle things.

Nostalgia Air has an excellent tube resource manual on thier site.

http://www.nostalgiaair.org/

http://www.nostalgiaair.org/Tubes/

Various other links will get you schematics etc.


Look up your tubes, get the correct pinout and mark schematic accordingly. Will help in identifying pins. Ask lots of questions as you go. Take your time, and enjoy restoring this beauty!!!

Rick


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 Post subject:
PostPosted: Mar Wed 09, 2011 12:34 am 
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Joined: May Mon 25, 2009 10:53 pm
Posts: 113
Location: Clinton, MI
Congratulations on finding a unique set. I have that same model. I found it about 16 years ago at a barn sale 6 miles from the small town I live in. I happened to stop by and couldn't believe my eyes! I had to count the tubes 3 times before I convinced myself what I was actually looking at.

My set was still owned by its original owner and they had consigned it to be sold at this barn which sold antiques.

Everything was pretty solid except for some flaking of finish at the bottom of the cabinet. The chassis was a different story. Some repairman in the past had done a fair amount of work and there were some mistakes as some of the parts were not replaced correctly. Once I got through the radio plays like a dream.

Power supply capacitors are a first! After you are through with that then replace the audio coupling capacitors in the audio output stage. The coupling caps can become leaky and it changes the bias on the tube causing it to conduct all the time. This condition can cause real problems to the output transformer and output tubes. So, before you apply power to the set make sure those are replace too. If the coupling caps are leaky it can also cause distortion in the audio.

Your radio is the only other one I have seen besides the one I own! Good luck with your restoration and keep us posted.

Take your time and do it right!!


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 Post subject:
PostPosted: Mar Wed 09, 2011 3:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 15757
Location: ID 83301
You do not need any variac or dim buld tester . You also do not need to replace ''all'' the wires in it . I have seen way to many threads where new people read and fall for this stuff and the radio ends up never working again .

As a new guy to this what you should do is first replace only the filter capacitors and the power cord if its bad then plug the radio in and see if it works and slowly work up from there .


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 Post subject:
PostPosted: Mar Wed 09, 2011 3:16 am 
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Joined: Aug Tue 24, 2010 8:56 pm
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Location: Florida
C'mon Ken, can't we at least give the power transformer a soft start? :cry:


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 Post subject:
PostPosted: Mar Wed 09, 2011 3:21 am 
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Location: Aurora Colorado
Welcome to the club, the chassis is nice and open, will be easy to work with.

Head out and get yourself a multimeter, that can measure up to 600v, a good solder gun and solder, and enjoy the ride.

David

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 Post subject:
PostPosted: Mar Wed 09, 2011 5:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 789
Location: Lawrence, KS,
Ben, A great find.

I have a 15S495 myself. It is a rare one, to be sure. Frank Rasada of Los Angeles had only seen one before I got mine. A total of 750 chassis were built and allocated between the 15S479 and 15S495. The larger 15S495 has the record changer in the belly.

It took some time to restore the original hookup wiring for the phonograph and to also get the original phonograph operating like new.

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 Post subject:
PostPosted: Mar Wed 09, 2011 5:23 am 
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Joined: Aug Thu 27, 2009 7:47 am
Posts: 2129
Location: Seattle
Ah this radio! We were looking at it and commenting, actually. Glad it's found its way to someone who will show us pictures of it during the fixing process!


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 Post subject:
PostPosted: Mar Wed 09, 2011 6:55 am 
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Joined: Feb Tue 02, 2010 5:20 am
Posts: 154
Location: Vancouver, BC
Hi there and welcome! You're going to learn a lot and have fun.

I see you are in Bellingham, WA. I'd strongly recommend a visit to the radio museum on Bay St. downtown, they would be able to give you great in-person advice in addition to the great help you will get from those in this forum.

It's the American Museum of Radio and Electricity, I think it is in the 1300 block of Bay. Friendly folks, and a thousand old radios plus schematics and advice.

My wife and I are members of the museum. We live just over the border in Vancouver BC.

Kevin

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 Post subject:
PostPosted: Mar Wed 09, 2011 9:23 pm 
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Joined: Mar Sun 06, 2011 11:41 pm
Posts: 6
Location: Bellingham, WA
Funny how forums have the same dynamics from place to place. I'm a longtime member of a motorcycle-related forum (Yamaha Triples) and it has a very similar flavor. Lots of friendly voices and welcoming advice - some conflicting :) I bet there's even the equivilent here to the infamous Gas/Oil/Tire "discussions" that pop up time to time and get people all revved up.

I have read numerous sources that say all paper and electrolytic caps need to be replaced - a thrilling prospect when I look at this. I think that regardless of whether I have to do them all or not, I'm going to start with the power supply side and one cap at a time. Too easy to predict what would happen if I tried to make a huge leap all at once!

Hey Kevin - it's probably a few too many visits to the AMRE that got me started on this lark. I have their broadcast streaming at work and usually listen to them at night when I'm wrenching in the garage.

As for where to start, I'm going to spend some quality time getting to know the schematic and sorting that against the physical layout. Just the way my brain works. I always need a solid mental picture of what I'm working on.

I've already found that someone swapped the rectifier tubes from the original pair of 5y4 to 5y3's. I gather that they are functionally the same, just a different pin-out. Haven't yet confirmed that they bridged the pins properly to make the different tubes work. Would there be any reason to change back to the 5y4 tubes?

Also, a question for Daveo50 and Martin - in the chassis picture I posted, there is a nice, shiny transformer at the far right. Is this the item labeled "spkr field, 275 ohms (hot)"? It makes sense as per the schematic and the way it's wired, but there is no part number given - which makes me wonder if that is really what I'm looking at.


Thanks everybody!

Ben


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 Post subject:
PostPosted: Mar Wed 09, 2011 9:38 pm 
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Joined: Aug Thu 27, 2009 7:47 am
Posts: 2129
Location: Seattle
triple.ratrider wrote:
Funny how forums have the same dynamics from place to place. I'm a longtime member of a motorcycle-related forum (Yamaha Triples) and it has a very similar flavor. Lots of friendly voices and welcoming advice - some conflicting :) I bet there's even the equivilent here to the infamous Gas/Oil/Tire "discussions" that pop up time to time and get people all revved up.

I have read numerous sources that say all paper and electrolytic caps need to be replaced - a thrilling prospect when I look at this. I think that regardless of whether I have to do them all or not, I'm going to start with the power supply side and one cap at a time. Too easy to predict what would happen if I tried to make a huge leap all at once!

Hey Kevin - it's probably a few too many visits to the AMRE that got me started on this lark. I have their broadcast streaming at work and usually listen to them at night when I'm wrenching in the garage.

As for where to start, I'm going to spend some quality time getting to know the schematic and sorting that against the physical layout. Just the way my brain works. I always need a solid mental picture of what I'm working on.

I've already found that someone swapped the rectifier tubes from the original pair of 5y4 to 5y3's. I gather that they are functionally the same, just a different pin-out. Haven't yet confirmed that they bridged the pins properly to make the different tubes work. Would there be any reason to change back to the 5y4 tubes?

Also, a question for Daveo50 and Martin - in the chassis picture I posted, there is a nice, shiny transformer at the far right. Is this the item labeled "spkr field, 275 ohms (hot)"? It makes sense as per the schematic and the way it's wired, but there is no part number given - which makes me wonder if that is really what I'm looking at.


Thanks everybody!

Ben


Spkr Field is the Field Coil on the back of the speaker. This radio was made before permanent magnets were of high enough quality to provide the magnetic field for a speaker to operate, so radios from this time used a field coil through which the B+ was fed to set up a field (and also serve as a choke.)

Not sure what that transformer is...the bottom of the power transformer poking through the chassis, or the output transformer?


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 Post subject:
PostPosted: Mar Thu 10, 2011 3:19 am 
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Posts: 4314
Location: New York USA
Here is a link to the schematic on Nostalgiaair http://www.nostalgiaair.org/Resources/770/M0024770.htm
The shiny "transformer" on the right is actually the filter choke, with only 2 leads, connected between electrolytic capacitors C23 & C24. The speaker field is connected between C24 and C25 for more filtering. Note C22 is not an electrolytic, but a paper capacitor that should be replaced too. This set should sound awesome when it is finished.
Don


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 Post subject:
PostPosted: Mar Thu 10, 2011 3:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 216
Location: Newark, OH
Gawd, resize those pictures! Much, much too large.

Having to scroll to read this subject is a real PITA. :x


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