Stromberg-Carlson Model 125

[TC Chris]

This radio is the current resident of the shop space.  It's a 5-tube, AC-DC set from 1937, with 2 SW bands.  It's basically an AA5 on steroids.  The RF section looks really serious.  But S-C makes it hard to service.  The capacitors don't have values on them.  They have part nos.  So you have to look up the location of the device on one page to verify that it has the right part number, then look it up  on the parts list on another page to get the value, and then check that o the schematic to make sure the numbers match.  The schematic is not one of those rational Sams layouts, where you can follow the circuits.  It has lines going all over, and the old fuzzy schematic I printed makes it hard to tell whether a line shows a connection to the ones it crosses or just goes past them. 

Then there's the extra filtering S-C used.  There's a 3 section electrolytic in addition to the 2 others in the power supply.  The can shows its values but not the color coding for the wires.  The schematic shows the color coding for the wires but not the values of the section they go to.  Tonight after relaxing my mind I went out to study it.  I followed the colored wires on the schematic and on the chassis it self to figure out which one was the low-voltage cathode bypass.  That means the other two are high voltage filters.  But I wanted to double check and make sure.  Think I've got it now.  Next step is to see if my capacitor stash has all the values I need.

Chris Campbell

[TC Chris]

I spent some time tracing out the wiring to make sure I knew which wires from the mystery filter cap were which.  The one that was 12 mfd/25V  was obviously the cathode bypass on the output tube, so each of the other wires must be 4 mfd./w150V.  I had close values but not quite exact, so I went to order them from Sal. Oops, Sal was on pause to catch up on orders. So I went to Mouser.  Found the right values and ordered a bunch extra, because (1) it's nice to have  stash of parts, and (2) the shipping was a large component of the total price, and adding little caps doesn't change the shipping cost.  Might as well fill up the box.

But then Mouser had its own issues, delaying the order for several days to catch up.  I just got notice that they were shipping today.  I ordered a week ago.

Meanwhile, the next time you're looking at a Sams schematic, KISS IT.  Be grateful for the full and complete info it provides and the logical way the circuit is laid out on paper.   The 1937 Stromberg-Carlson pages require you to look at all three pages--the schematic, the parts diagram, the parts list--to figure out what a component is and where it's located and what its value is.  What a pain.  And the schematic shows what's connected where, but it takes a lot of tracing with colored pencils to figure it out.  Nothing logical at all about the way it's drawn.

Chris Campbell

[TJ]

Mouser was running behind on my last two orders with them.  I ended up doing an order with Digikey after waiting a week and a half and got everything before mouser even was ready to ship, the mouser parts are now in the parts stockpile.

Are you using riders schematics?  Sounds like what I have had to do on the Philcos that I have worked on.  Multiple pages to make sure I was doing the right part.

The 1932 Motorola radio I did only had a rough schematic pasted to the inside of the cabinet.  I had to redraw it by hand, write the pin numbers of the tubes as they were not listed, and do some guesswork on how to interpret some of the work from the schematics and how it was in the cabinet. 

[Bill]

Trevor, 

Are you aware, or have you heard of Nostalgia Air?  I have had real good luck finding vintage service info on that site.

http://www.nostalgiaair.org/

Bill

[TJ]

Trevor, 

Are you aware, or have you heard of Nostalgia Air?  I have had real good luck finding vintage service info on that site.

http://www.nostalgiaair.org/

Bill

Yes, I looked everywhere, it was a relatively rare early Motorola table top, when they were still focusing on Car radios.  I was able to find the same crude schematic online, but that was it.  This was one of the radios I redid for my Uncle, I also redid his '37 Philco tabletop.

[TC Chris]

My Mouser order arrived yesterday so I could re-stuff the 3-section electrolytic and I got that done today.  A new dial glass is on order because the original was was broken when my Scoutmaster gave the radio long ago.  The parts were all there and I glued them together, but they looked awful.  So even before making sure the radio was going to work, I ordered a new one.

Last night I tested the tubes; all OK.  It reminded me that when the radio came to me, several tubes were missing or dead.  That was long before the internet, when you had to know tube suppliers and get their periodic lists in the mail, or write to them with a request, get an answer back in the mail, then send a check, and wait for the tubes.  Wow, folks, let's appreciate the internet!   

As far as I can tell, none of the tubes are original, so this old radio has either had lots of use since 1937 or it got zapped by lightning at some point.

At any rate, as soon as the caps were in (and mind you, this radio has four filter caps and two filter chokes in the power supply), I decided to plug it in. It is an AC-DC model, so no transformer to burn up.  I connected an antenna wire, plugged it in and turned it on, and damn! It works!

Now what it needs is a felt gasket that goes between the speaker's cardboard gasket and the cabinet--about 1/4" thick.  (The whole thing is 5-1/2" ID, 6-1/4" OD).  Any suggestions for sources?

As soon as the dial glass arrives and I work out some sort of edge seal for the speaker, I'll work up a little YouTube video and post a link.

Chris Campbell

[Bill]

Being a person that has worked on pipe organs, felt is something that I'm familiar with.  When I needed felt, and it depended what size and thickness I needed, I would first start at a fabric store.  If they did not have what I needed I would turn to either a piano supply company or an organ supply company.  Try:

www.organsuppy.com
www.arndtorgansupply.com
www.schaffpiano.com

Good luck Chris,
Bill

[TC Chris]

Thanks for the tips.  The Schaff site had some felt options that might work.
Chris

[Bill]

 

Bill

[TC Chris]

Here's a link to a YouTube video on the S-C 125H restoration.

https://www.youtube.com/watch?v=btqPZvnVCzY

The radio was a gift from my scoutmaster over 40 years ago.  He also gave me the  Philco 38-15 that's in another one of my YouTube videos and got done first.

Chris Campbell

[Bill]

That's a good looking Radio Chris, and it sounds good too.

Bill

[Motorola Minion]

I can appreciate your difficulty with that S-C schematic. A Crosley, RCA, GE or Philco from the same time would be similar. I bet that different departments wanted their own document to reference. One was assembly, the other supplied parts and the

Rebuilding those condenser blocks in a Philco requires cross referencing and figuring out what parts Crosley used in some of the "fiver" series was equally challenging with those wiring maps.

That said, the variable condensers really are a sweet detail on that S-C. For a 5-tube set, that level of quality to fine-tune its RF and IF is seldom seen.