Hi all,
have just obtained a Stromberg-Carlson the model I think is a M-41. Valve line-up is 6JB6, 6U7G, 6B6G, EL3G, 5Y3G, although the 6JBG has been replaced with a EK2G and the EL3G replaced with a EL3N.
I'm after a wiring diagram for this and any tips, comments re this radio.
Also I would like opinions on capacitors, ie replace all paper wax & electros, replace only non-spec or defective, replace none if radio works fine.

AORSM's only show M-40 you may be lucky and it also built in America? Check Nostalgia Air.

The converter will be a 6J8G, the one in it is a Philips equivalent.
M40 used a 6V6 EL3 Philips is a higher gain valve & will have different circuit values than 6V6.

Standard practice is to get rid of all of the paper capacitors, the Mica rarely fail. Electrolytics tend to dry out. noticeable hum or evidence of leakage, will give the kiss of death to the electrolytics. Some of these may already have been changed. In an old set like that. I tend to change all electrolytics.

Also pay attention to the power cable and its anchorage. Nowdays one changes to a three wire cable.

Resistors can be checked if they are unsoldered to change caps. You can get errors if you test in circuit and there is a DC path.

Also check the condition of the wire as some of this in many sets deteriorates and risks shorting.

Marc

Thanks Marc for input
I assumed model No. from the no. on the back- M4183988 with the 41 printed slightly differently. The date of assembly 9/7/1942, written in pencil on the back of the transformer (very difficult to see, need the light in the right direction).
I then used Paul Ledger's web site and the model m-41 seemed to fit.
A M-41 is listed there.
http://www.keypoint.com.au/~pauledgr/Stromberg_Carlson.pdf

OK I have sprung the circuit for both, the page was missing.

Both of these circuits show 6V6 as the output. Only a real early model shows the EL3N.

EL3N requires around half the grid bias of 6V6. The only way to tell from the circuit I see is to measure the grid voltage. It may be a factory mod. due to wartime shortage?

Marcc

I agree with Marcc's approach as it is a basic but essential safety routine. Back when I started collecting twenty years ago it was more common to plug in a radio you just acquired and expect it to still work.

It is still hard for me to imagine though that many of the radios we all love having in our collections are now more than 60 years old and these are still the commonly available brands and models. Sadly after 60 years of service something has to give and yes, it is usually the condensers and the power cord.

The valve line-up printed on the chassis has the EL3N printed differently as though it was an addon, so your idea of a wartime shortage makes sense.
Marcc could you send circuit to me?
My email is flyinghigh747aapt.net.au

Three (related to one another, so you need the lot) sent.

Do read the notes on the bottom of the sheets there is reference to how they established the self bias on the 6V6. The resistances will be different for the Philips valve.

Do not put an knot in the power cable, that is no longer legal.
In many sets (not all) a gland is much more effective.

If you look at July & August "Silicon Chip" you will see how I did those two. You can have the gland stick in or out and it just as effective, if there is room. There are other forms of clamp.

Marc

As a rule I still use rubber grommets to keep the look original but attach the cable inside the set with one of those nylon strap type clamps similar to Jaycar Cat. #: HP0752 kept in place with an existing machine screw and nut.

Brad, I not this site & passwords in Firefox have issues, awitced to IE7.

I tend not to use that type unless I can get an anchor. I will use grommets, if there is a space issue. As I tend to use three wire cord the IP68 gland will stop the cable from rotating as will HP0716 (not preffered. A burndy will stop any chance of it "pulling".

The IP68 long end inside does not look all that out of place. The Object here is safety above all else. Also leave the earth leg longer.

If it the cable gets used for a tow rope, and the wire breaks; There is a better chance of the earth being the last to go, preventing live chassis.

Marc

Have already replaced cord with 3 core and went down the grommet & clamp path but as you say Marc glands do make a lot a sense, also sleeved the transformers primary (bare conductors) then did an electrical safety check (shorts, loose wires etc)

Radio was then fired up and after a nervous warm-up the footy came on. There is a slight power hum is this usual or is it the ageing filters? I will be replacing caps in time

Marc I got the circuits and would like to thank you for notes and making the time to send them and to Brad for his input.

I have got a bit of homework to do on valve radios as my experience is in solid state electronics (was an electrician in an earlier life) everything is bigger and relatively simple though. Valves just seem to be oversized inefficient transistors

There are a few things that valves can do, that transistors will not and with a lot less of them,despite so called inneficiency.

Some hum will be evident in some sets due to "hum modulation" via the heaters. It can also be caused by the transformer being overloaded and of course dried out filter caps.

The newer type caps sometimes reform, however, I have only left about six electrolytic caps unchanged, in the last 130 Radio's. Replacement is the best policy.

Marc