Hi all, Wondering if anyone can help identify parts on this 1937 stromberg carlson model 537
6a7 ,6k7 80 75 al3 also with magic eye.6g5

This is the first project ive done solo, and any help would be gratefully accepted,as I'm very new to this.

Ive cut power cord, needs replacing and earth, replaced all wax caps, all electrolytic capacitors,and checked all dogbone resistors which are surprisingly good values.The voltage divider resistor, had 2 bad spots so ive replaced equal value across terminals of bad section. which leaves me to the 2 canisters in photo. there was 3, one was clearly marked electrolytic capasitor 8mfd 525v , But I'm not sure on these 2 others, elec caps?,they dont have usually connections at bottom and their joined together ,but they are insulated on the bottom and top, theres rubber or plastic,3 wires comming off them,,1 wire goes to the amp ..ct ,and another to the volume and a 10 μF 40v electrolyic cap also comming of them going to ground?

Thanks for any ideas

On what you've given, closest I can find is model 537 from 1937:

http://www.radiomuseum.org/r/stromberg_537_2.html

There is a single wave model 667 & dual wave model 6237, both from 1937. The valve line-up is as follows:-

6A7, 6K7, EB4 (P-base twin diode), 75, AL3, EZ3 & 6G5 eye tube.

Is there an extra valve you might of missed? The EB4 usually is red and quite small. The bulb is similar dimensions to a 15W light globe.

The 80 rectifier is an odd one. None of the 1937 models listed in the AORSM used them. All the 1937 models used the 6.3 volt P-based EZ3.

Is there an extra valve

That's what I was thinking, too.

I am looking at 1937 Trade annual & neither of those numbers are consistent with it. 6K7 is not a valve commonly found. There were 3 Variants of 6237 which is what I think it will be...there is a C & G but no indication as to what they did? AL3 probably ended up as EL33 & the rectifier was changed.

Two things AL3 has a cathode sleeve and is slow warm up: 80 is not and will create a HV surge. Circuit is in AORSM

Weird things happened during wartime, with a lot of chopping& changing, where manufacturing of domestic radios continued.

The crazy cap setup is logical. The first electrolytic that better be replaced by 500V or better is not grounded. As the set is "Back biased" and the centre tap of the HV secondary will ground via a resistor or part of that multi tap one. That means that the first cap goes between CT and the 80 filaments (Big pins) and that filament is floating also (no ground). The second one grounds (no photo at time of writing). and may be attached to the screen of the AL3 (pin7).

There is a cap CT to chassis, the difference there is it will be positive to chassis 40V is common there. I would expect 6V across it in this set.

be careful AL3 has 4V Heaters on a separate winding.

Marc

Thanks for the fast response,Ive up loaded photos,a bit hard to describe with out pic,but All the valves have been stenciled on to the chassis ,6a7 ,6k7 75,Al3 and 80.

From th AORSM, vol 1 , (copy from library) , only 2 models 6237 and 667, have have the same valve line up but inplace of 80 they list.. EB4 Dem.A.V.C.No other models lists the valve line up

The 2 canisters in question, are connected together,from photos, But dont appear to be grounded anywhere only a 10μF 40v positive side to ground,coming of that same connection.Thats why I just wanted to make sure, electrolytic caps.dont always have to be grounded.

As it is back biased, it is common for the first cap to be hooked to the floating centre tap. As the cap across the backbias is also connected to to the CT, it would be quite logical for both to be in the same can and essential that their negatives do not contact the chassis.

Do consider that when replacing & it is easy to achieve with individual caps, kept away from the chassis.

Marc

Thanks Marcc for your reply,
Yes, just isolate negatives.There is no clear values on the Electrolytic Caps,( faded), going by the 6237 circuit diagram 40 mf and a 10 mf, havent been ticked off,with this being a Variant, would it be possible the values would be the same or at least in that range ?, thereby replacement same or slightly higher μF with higher voltage.
regards John

The model number should also be stencilled somewhere on the chassis. Stromberg Carlson receivers of that era usually incorporate the model designation with the serial number.

In the case of models 667 & 6237 both the 75 valve diode plates are tied to the cathode. The EB4 in these models performs the functions of what you'd think should be done by the 75 diode plates. It seems to be a waste of a valve.

Going through the Mingays 1938 trade annual there is listed a broadcast only model 57 (sorry no circuit) with the valve line-up of 6A7, 6K7, 75, AL3 & 80 (no eye tube). Checked the 57 circuit in the AORSM and the valve line-up differs:- 6A7, 6D6, 75, AL3 & EZ3.

Armed with this information I'd certainly now go with GTC's suggestion of the model 537 for a road map.

Hi MonochromeTV,
numbers stencilled across the back 53757497 a bit of of both?

Model 537 & Serial No. 57497.

Thanks for that information,its much appreciate,will give me an idea what to work on. Back to the library.

In the socket of the eye tube is normally a 1M resistor, the attrition rate with those is around 99.9% out of spec.

Marc

Thanks Marc, will check that out also.

Just wanted to say Thanks,Marcc,MonochromeTV,GTC, for your help and advice,Got the Stromberg/Carlson model 537 up and running,Magic eye working,Sounding Great.Thanks again, Joerik