Emerson 637A Restoration
 

Time to start another restoration. This one is an Emerson 637A chassis 120095-B. A series string hot chassis.

The cabinet is in nice shape and will clean and polish up nice.

The chassis looks to be in decent shape. There is evidence of prior work being done. Besides the usual electrolytics being changed, a few caps were also changed, the main selenium rectifiers were by-passed with some diodes, and some adjustable resistors were wired in on a terminal strip. The sheet metal needs some cleaning but has very little rust. A lot of the tubes are missing. Mostly 7 and 9 pin miniatures.

As far as I can tell there is no full Sams on this chassis, only a schematic which mirrors the one in Riders V6. Riders V6 has the alignment procedure, and parts list.

The 10BP4 CRT tested a little weak but my Beltron came to the rescue and now shows a 20 second dely before the needle drops. On my BK 467 it shows a good strong 1.2 on the meter. The dag coating is mostly gone and will have to be redone along with gluing the loose base.

It does not have a back. Which leads to the first request. If anybody has one of these with a back, could you send me a picture of it? It would be really appreciated.

Also there is a 5W? resistor sticking out of the tuner near the front. I didn't see it on the schematic. I think it is about 21 ohms. Anybody know what it is used for and if it is OEM?

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"Also there is a 5W? resistor sticking out of the tuner near the front. I didn't see it on the schematic. I think it is about 21 ohms. Anybody know what it is used for and if it is OEM?"

Likely a current shunt for the heaters of the tuner tubes... my 639 has a similar repair, as one section of the under chassis resistor is open and was replaced by a resistor mounted on the top of the tuner.

Nice looking set, one of my favorites (that I have not collected yet).

jr

The 6J6 is a different heater current than the rest of the tubes. It must be less than 300ma as the rest of the tubes are.
Also, the 6S8GT audio tube is missing. Emerson seemed to like that tube.

As I understand it, the series connected 300 ma tubes are arranged in 2 parallel strings to total 600 ma that feed the CRT heater (600 ma) and the 6J6s (450 ma shunted with resistors to make 600 ma).

jr

You are correct. There is a Candohm resistor inside the tuner which is a 2 section resistor. One section is 27 Ohms (measured) in parallel with the 6AG5 300ma heater pins, and the other is 47 Ohms (measured) in parallel with the 6J6 450ma heater pins. This then allows 600ma through the tuner string. There is also that 1 resistor on the outside. That is 15.6 Ohms (measured) which is in series of the entire filament string. Bringing the entire filament string to handle up to 130V.

I didn't get much done today. Did figure out the filament string. It'll work great!

I did manage to label all the resistors, capacitors, pots, inductors, and coils according to the schematics from Riders V6.

It seems that this might not be a 120095-B chassis. There are no markings to tell me what it is. Looking further in Riders V6, I did see another schematic for a 120138-B chassis that does show the correct speaker field and voice coil connector along with some added and subtracted resistors and capacitors that were in my chassis but not on the 120095-B schematic. However, the 120138-B schematic does use a 12BH7 instead of a 12SN7GT and uses a 12AT7 instead of a 12AU7. I did use the combination of the 2 schematics to label the components. I could not find a schematic that really matches my chassis.

Yesterday I drove to Mouser (an easy 20 minute drive) and picked up my E-Caps and some Micas. I had everything else here.

Tomorrow I'll start cleaning the chassis and working on the power supply sections.

Yeah, I pulled the Tuner to figure out what was with that resistor and discovered a Candohm resistor inside the tuner. More on that when I restore the tuner.

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That tuner looks like an Admiral and I have some NOS replacements.

Yeah, that's what I thought. I'll keep you in mind if I need one. Thanks.

I restuffed the E-Caps today. I usually use Nichicon 105 degree caps, but this time Mouser had some from a new supplier. The specs looked good and they all had a 12,000hour rating! So I ordered what I needed. Here is a link:

https://www.mouser.com/ProductDetail...XL451ELL121MM3

I used my usual method of using a PVC sleeve. All of these E-Caps has a cardboard cover so I made the parting surface up from the base. When the can goes back on I'll run a layer of tape over the seam to secure the can and then slide on the cardboard cover.

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Nice set! Those were shunned back in the '80's, but they sure look good today. If you can't find a back, look up perforated steel sheets on eBay. With snips and grinding wheel you can make a real nice convincing back. Some use fiberboard (which was likely used originally), but it's a bear to make the many ventilation holes straight and clean-cut.

I picked up a similar 648A a few years ago that I have since sold but did take some photos.

Here's one of the back. I also
https://flic.kr/p/6okuzE

I also have an Emerson 637A with back but it is in a wooden cabinet and a model 614 in bakelite.

Here are photos of my 637A https://www.flickr.com/photos/700398...57672714173057

Are you sure about your model # ? I'm pretty sure you actually have a model 614D

I got my 614 a while back from the Eli Buk auction but have never taken the back off or looked inside. It may very well have the same series string chassis you have. It's currently in my storage locker. I'll try to take some photos next time I'm out there.

Bob, no I'm not really sure. Rider's index shows 2 models with Ch. 120095-B. A 637A and the 614D. It looks like it might be a 614D model because there is no transformer.
Now your pictures of a 637A has a transformer. If you are sure yours is a 637A, then Riders must be wrong.
It's a challenge sometimes to figure this stuff out.
Your help is appreciated.

Yes, I'm sure mine is a 637. There are numerous photos of 637s out there that match mine like this one on the Radio Attic. https://radioattic.com/item.htm?radio=1310025

I see hwat you mean about the power transformer though. Seems that the 637 'A' should be series strung. I can't say for certain if mine is the original back or maybe it's a factory screw up ?

Here's an original Emerson service manual depicting the various models on it's cover including the 614 and 637.
https://www.manualslib.com/manual/81...erson-614.html

I'm really curious to see what chassis is inside my 614 now!

The 614 on the Emerson Service manual has 4 controls on the front. IIRC there was an Emerson Service Bulletin/Doc? that states the top 2 controls were moved to the back but with no wiring changes. Maybe with the control relocation and going to a series string it became a 614D.

EDIT. The relocation of the controls is indeed in the manual you linked to page 28.

I installed the E-caps and wired them in today. While I was working in the corner I also took care of some of the audio section on the terminal strip and volume & contrast pots.

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Then I did the other E-Cap on the opposite corner of the chassis. This E-Cap was a 3 section cap and was previously replaced with a 2 section cap and a separate 100uf cap just "tacked" in using a terminal strip. It was pretty evident what was done and it was fairly simple to restore that section back to OEM.

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Here's a fun picture for ya. Here is the pile of components that I'll be using during this restoration. Missing are 7 E-Caps.

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Today I ohmed out the transformers and coils. They all checked good!

I then decided to redo the chassis from the HV section back. Basically got all the components from V14 (Damper tube), Fly Back, V12 (H Output Amp), and the safety cap.

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Moving from the H output toward the H. Osc. section. This terminal strip was a toughie. Lots of wires and components. Between church, football, and family, this was pretty much all I got done. BTW, the mica capacitors were changed and the ones I pulled out were C-72 was 17%, C-75 was 17%, and C-76 was 14% out of tolerance. This just reinforces that they do go bad especially in the sweep circuits.

If you haven't noticed, when I remove a wire from a terminal, the end gets cleaned up and then a small 3/16 or so length of clear heat shrink is put over the insulation to prevent any future fraying. It sure neatens up the job.

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Took are of V11 and the H. Osc. section today.

On to V10 and the Vertical section.

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Moving upstream I've completed V9, V4, and V5. Next up V6, V7, and V8.

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Getting close.

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Oh no! On power up I wasn't getting any audio. So I wiggled the tubes in their sockets. Still no joy. Then I pulled each tube to clean the pins again and to inspect each socket.

Look what happened! Yeah, pin #1 on the 6J6 tube stayed with the tube. Now I have to pull the tuner again and see if I can fix it. Any helpful hints will be appreciated.

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Also on another note. No high voltage either. I'm thinking that the H. Oscillator isn't running. But I'll check into that later.

Just pull the bottom solder tab down a bit slide a new contact from a similar socket in from the top and solder the tabs together under chassis. That is the least intrusive method.

I have to pull the tuner so it'll be a few days before I report back. Thx

I found the time tonight. I had an old Motorola chassis that had a similar tube socket. After robbing the socket, I cleaned off the solder on one of the pins, then I used some short needle nosed pliers to "flatten" the small indentation in the contact. I then used some small narrow duck bill pliers to push it up and out of the socket.

I then cleaned up the contact. Ready for the tuner.

I pulled the tuner and removed the turret. Lucky me. the #1 pin on the 6J6 was the easiest one to get too! I removed the solder and the resistor and jumper wire from the old contact.

I inserted the "new" contact and used a small flat 1/8 dia. pin punch and a small hammer to drive it home. It felt secure.

Then I rewired the contact with the jumper wire and resistor.

I then tried the tube in and out several times. Good to go!

Thanks to ElectronicM for the suggestion.

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I reinstalled the tuner and now I have sound.

I then found a 12SN7GT bad. I had it listed as bad but installed it anyway! I replaced the tube and now I have HV!

I put in the 10BP4 CRT that I cleaned up and restored the DAG with Slip-plate.

A few tweaks on the back panel controls and here is what I have. The CRT works very well! Of course I'll have to take some time to align it and set it up.

I do have an annoying 60 cycle hum/buzz in the sound. After I align it if it is still there, then I'll look into it.

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That chassis probably looks better than it did when it rolled off the line. Great work!

I love following your restos. Photos are so clear and your method so logical. A pity that vintage TV's are so rare in Aus. Only done one so far but itching to do more after following yours.

How did you get that chassis to look so good? It almost looks like you re-plated it.

After I cleaned and took care of the rust spots, I primered it and then used Rust-Oleum Matte Nickle spray paint.

Did a little adjusting today. Tomorrow I'll start the alignment.

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Been busy with other things.

Here's a picture of all the caps and resistors that I changed out.

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Update!
The chassis is finished. It's been aligned and detailed. The final set up will have to be done once it is installed in the cabinet.

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I've cleaned the cabinet inside and out. I also polished the outside. I filled in the lettering on the front knobs and the logo with gold paint. I'll spray on a new coat of gold that surrounds the CRT tomorrow. I got the paint from the craft section at the local Walmart.

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That is looking very sharp. Personally I'm not a huge fan of painting chassis and parts. I guess I just like seeing some patina on old things. I can live without the dirt, but all the little blemishes just add to the nostalgia experience for me. But I have to admit you have an awesome skill set and you make these look about as perfect as anyone could possibly ask for. The gold paint really makes that lettering pop. Overall you've done a knockout restoration. :thmbsp:

Gorgeous!

Excellent!

Thanks guys.

Excellent work. I can't wait to see it completely assembled.

A couple of questions!
What was that small selenium rectifier used for?
The octal tube base next to the 19BG6 has what in it. I saw one 60 years ago and that set had one that had a neat little perforated metal cover on it.
It seemed to be a surge limiting resistor in it, but a tiny one.

Looks like it is used to create the -150V buss.

That socket is for a Ballast resistor. On this chassis, it was just a piece of wire.

Both can be seen on the schematic below.

BTW, Emerson had drawn the symbols for the diodes backwards. My pencil marks are the correct way.

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