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.