[Eric]

I have a Stromberg Carlson 1121 Series 11 console it has been recapped and plays but has the 60cycle hum which is louder than it should be. Should I increase the filter cap value? Most of the tubes are metal enclosed is there a resistor that I should look at? Any Ideas??


Eric

[TA Forbes]

Take a look at the filter circuitry and power transformer. Never assume previous technician's work was correct. Is placement/polarity/value in accordance with schematic?

Is power transformer a replacement?

What are filter cap replacement's values compared to what is called for on schematic?

Was radio totally recapped or just electrolytics in filter circuity?

[TA Forbes]

Terry, am I forgetting anything?

[codefox1]

Agree, and please post image or link to schematic. Old repairs may or may have not been done correctly. There is little to gain from increasing values of filter capacitors unless a field coil choke has been cut out and a PM speaker installed. Then, yes, but mind the specs for the rectifier tube.

If you can, swap the output tube(s) with known good ones. Many times gas or other defects cause hum. Of course lots of "modern" gadgets cause all kinds of havoc with antique equipment. Dimmers, battery chargers, computers, portable phones, flourescent lamps, new lamps, modems, etc....

[TA Forbes]

Good point. 6V6 output tubes may have been replaced with 6F6 or 6K6s.

[Eric]

The one of the cap values was light should be 40 and it came in at 33 so I changed it seems to be better. the speaker is not original. Also I'm finding that the phono has a pretty good buzz when it's on I can soften it with the tone adj. will open up the amp and see what is in there. The print is in Riders 15-17

[Arran]

Test your tubes for heater to cathode short circuits as well, if you don't have a tester try substituting one tube for another. I'm betting that the problem is likely an incorrect negative connection on a filter cap, it's a very common mistake. Many people wrongly assume that the B- connection is always to the chassis, but 1930s era radios ( and some 1940s era ones) often used a fixed bias supply with large wire wound resistors, so the chassis is slightly less negative then the center tap of the power transformer. Another mistake that people often make is that they assume that the field coil of the loudspeaker is always in the B+ circuitry, sometimes it's in the B- circuitry, but it does still act as a filter choke regardless of where it is connected.
Regards
Arran

[TA Forbes]

If the speaker is not oiginal, was it replaced with a PM speaker? If so, what was used to replace the field coil?

[Eric]

Speaker is not a PM and resistance of the coil is 958ohms print calls for 950 so that looks good. the console is from 1947
Have a Hickok 6000a and will run through the tubes. Thanks

[Arran]

I sort of figured that your set may have been from the 1940s, I have a model 231 and it's from around 1937-38 vintage so if they were consistent then the model numbers would go higher as new models came out. In which case since it's a late 1940s set then the original filter cap was probably a multi section twist lock can with the can grounded to the chassis, by the way the set should also have a filter choke but if it were open the set would not play at all.
Regards
Arran

[Radioroslyn]

Hey Tom
Yous guys are doin' fine.
Terry

[Conelrad]

If it is indeed 60 Hz hum, it most likely isn't the power supply area...that would have 120 Hz ripple if it derives from a full-wave rectifier.

60 Hz stuff usually comes from filament circuitry, or an external ground loop.

Dennis

[Eric]

Changed the filter caps to bring the one up to the proper rating also changed the 5u4 and the hum is gone. Thanks for the help.

[codefox1]

Yupp!

[TA Forbes]