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Stromberg-Carlson 225-H - Printable Version

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Stromberg-Carlson 225-H - morzh - 09-16-2013

Well, here goes....

I started on it today. I am not in any rush, will take my time.
As I wrote before, the ballast tube, despite its rusty looks, is actually fine.
Need to clean it up with something that would remove the rust.

The radio was repaired before, hence the two DC filter electrolytics missing - replaced beneath with tubulars. One of the electrolytics, the one that is not used in the DC filter, is still conencted. All tubular paper caps are original, though 3 or 4 have been replaced.

Now, the speaker: the output xfmr is there, but the speaker is a PM, a new type, probably 50-s / 60-s.
In the schematic the field coil is plugged as a load - in parallel to the B+ voltage and is not used as filter, there is a separate choke for that.
Now this got me thinking: I do not know if the Field Coil was enough of a load to somewhat lower the DC (B+) voltage, and if it was, then I might be running at a higher voltage. Which probably is not good. I would not know that without knowing what resistance the Field Coil was.
I also do not know what voice coil impedance is expected from the original speaker and whether the new one I have is the same.
Good thing, since the voice coil is not used as a filter I do not have to come up with stupid things like replacing it with ballast resistors etc.

Well, here's the start.
If someone has the info on my questions - could use help here.

RE: Stromberg-Carlson 225-H - BrendaAnnD - 09-16-2013

The FC in my Monarch table model, close to the same circuit, was, IIRC, 7000 ohms. Seeing as you're using a half wave rectifier circuit off the line, your B+ is limited to around 130V or so. Given that, there should be no problem without that FC in the circuit. On mine, it was on the other half of the rectifier (designed as a full wave rectifier tube (25Z5?)) from the main B+ supplied to the radio.

On the ballast, naval jelly is good for removing and stopping the rust. Then use Krylon grill paint (high temp) to repaint the ballast

RE: Stromberg-Carlson 225-H - Mondial - 09-16-2013

As Brenda said, there should be no problem with not having the load of the parallel field coil. In fact the set should work better without the extra load on the power supply.

Keep in mind the same tubes would operate with a 250 v supply in a transformer set, so if your DC supply voltage goes from 120V to 130V all the better as to performance. You can always run the set on a variac and confirm that the tubes are operating within ratings as you bring up the line voltage.

I would not be too concerned as to the actual match between the voice coil and output transformer. Its really not that critical. Most speakers from the mid 30's to early 60's were 3 to 4 ohms, so the replacement probably is close to the original.

RE: Stromberg-Carlson 225-H - morzh - 09-16-2013

Brenda

Coke contains H3PO4 so maybe I just dip it in a glass of Coke Icon_smile

I have black enamel for Kenmore gas range top, shoud be temp resistant.

Need a couple of old bad electrolytic cans to plug the holes in the chassis....maybe I will buy those replacement caps they sell.

RE: Stromberg-Carlson 225-H - morzh - 09-17-2013

Bough Naval Jelly in Home Depot, the tube cleaned up pretty well, then I used the black enamel for my range top to paint it.
I am sure the paint job will not look pro but as long as it is protects the tube that's what matters.
And the odour is minimal.

Brenda, thanks for the advice. Never used that stuff before.

PS. The color of it (pepto-bismol) and the smell may actually make someone taste it. Though thinking of it, it is corrosive but not really toxic.

RE: Stromberg-Carlson 225-H - morzh - 10-02-2013

Almost finished replacing parts - all caps are done but lytics, and almost all resistors that need to be changed.
I am looking for a couple of junk 1-3/8" diameter lytic caps to re-stuff, does not matter what's written on them.
I do not have any junk ones.

I of course could temporarily just solder regular Al. can lytics in place......but I'd like to finish it properly, otherwise i will have that gnawing feeling of unfinished chassis restoration.

RE: Stromberg-Carlson 225-H - morzh - 10-15-2013

These caps really hold me up. Anyone!!!!!!!!!!! Need a couple of bad can caps. Will buy!!!!!

RE: Stromberg-Carlson 225-H - Jamie - 10-15-2013

Morzh,
I've got a couple of spare chassis from some 1946 consoles. Sorry for the blurry photo, but both chassis have the same can. If these look like they'll work, you can have them both for free. I can get 'em in the mail tomorrow or the next day. Let me know..

   

RE: Stromberg-Carlson 225-H - morzh - 10-15-2013

PuhPow

Thanks, the diameter I have is anywhere from 1-3/8" to 1-1/2", need two. It does not even matter what type it is, insulated or not, it is held by a clamp and the stuffing will be fully insulated.

Mike.

RE: Stromberg-Carlson 225-H - Jamie - 10-15-2013

Well, quit fretting over it. I've got a lot of radios here to work on. If no one else offers you any, I'll get some for you in the next week or so. Temp solder them in and don't worry about it.

RE: Stromberg-Carlson 225-H - morzh - 10-15-2013

I'll just wait - I am in no real hurry, but the way that chassis is done, the busses and bunch of wires were actually held by those caps' leads, so wiring the temps is a waste as the leads are real thin.
Actually this is the first time I see that: they used really thick rigid wires for busses. So far I have just seen the wires starred together in old radios.

RE: Stromberg-Carlson 225-H - Arran - 10-16-2013

What kind of filter cans did the Stromberg use? Was it the kind with a threaded nipple on the bottom or were then held in with a clamp?
Regards
Arran

RE: Stromberg-Carlson 225-H - morzh - 10-16-2013

There are two types. The one I am missing are the two rectifier filter caps, and they are clamp-held, from which I surmise they were two-terminal type.
The other is still in place and it is a screw type with 4 wires coming out, as it contains 3 caps inside, with the common negative referenced to B-.
Interesting thing is that although it does not look like an insulated type it in fact is as though the can is in contact with the chassis (and it is a screw type), the chassis itself is not connected to either of the power nodes. That is the chassis is not really "hot". It is connected to the negative via 0.2uF cap and serves as RF part's common, I think.

RE: Stromberg-Carlson 225-H - morzh - 11-10-2013

OK, so I stuffed all the caps, fully disassembled the dial, took naval jelly to it....then I realized it cleans it really bright.
And the Windex left most dirt in the chassis. Alcohol was better at it but not all the way.
I took a little Naval Jelly....and applied it, a little, to the top of the chassis. The result is spectacular. I washed the rest off with many towels and alcohol.
I also soaked the tuning cap in the dishwashing liquid. Came out sparkling.

That was yesterday.
Today I reconnected everything, soldered in the new cord, and after making sure the rectifier works (I need all tubes for that, that's the AA5 for you with serialized filaments), soldered in the speaker.
I have a small pigtail for an antenna.

It starting whistling and whining and eventually received my local station right about where it should be.
It is still whining, so I think I will have to spend some quality time with it although first I will try a longer antenna first.

But....it is alive!

RE: Stromberg-Carlson 225-H - Paul Philco322 - 11-10-2013

Nice work Dr. Morzhenstein! Now how bout that big green dude on the table...

Paul