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 Post subject: Humming on AA5
PostPosted: May Fri 20, 2022 4:13 pm 
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Joined: May Thu 19, 2022 9:04 pm
Posts: 5
I am new to this, so please be kind. I have a circa 1948 Stromberg Carlson model 1101-01. When it came to me it didn't work so I recapped it as best I could, replacing the "can" electrolytics with discreet caps. It does work now but I have a severe hum which I think is 60HZ. The hum gets louder when turning up the volume and/or tuning in any station. I tried running the unit on DC but the hum is still there. My other (more contemporary) radios do not hum on AM......any help here? :?


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 Post subject: Re: Humming on AA5
PostPosted: May Fri 20, 2022 7:19 pm 
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Posts: 20566
Location: Mountains of Mourne. Ireland.
Are you sure about suffix -01?

Verify that you have not miswired a component.
If you have applied power to an Electrolytic capacitor connected backwards, discard it.
Sams schematic, image: https://tinyurl.com/yt7r69zh

Sams Photofact Set-2 Folder-9 for model 1101 can be downloaded from Tom Bavis' website... in DjVu format.
This link will take you to Tom's Stromberg page. (Made in Rochester).
https://tinyurl.com/made-in-rochester

------------

I use this DjVu reader (safe download from sourceforge.net) works great.
http://www.antiqueradios.com/forums/vie ... 9#p2746819

If you are using a Windows computer, here is a direct link to the DjVu reader .exe file.
https://sourceforge.net/projects/djvu/f ... rror=netix
Save it to your desktop, open it and follow the installation instructions.

------------

Welcome aboard... :)
Greg.

Posting photos to a forum thread.
cartoon→ viewtopic.php?p=3346966#p3346966

(P plate) - (K cathode)


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 Post subject: Re: Humming on AA5
PostPosted: May Fri 20, 2022 10:39 pm 
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Thanks much for the help. The schematics I can find show 14 volt tubes but my unit has 12 volt tubes. For example; My unit has a 12SA7 which is listed on the schematics as 14Q7. So I am assuming that the voltages on the pins would be different on my unit.....sorry so dumb. :?


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 Post subject: Re: Humming on AA5
PostPosted: May Fri 20, 2022 10:48 pm 
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ricardogi248 wrote:
Thanks much for the help. The schematics I can find show 14 volt tubes but my unit has 12 volt tubes. For example; My unit has a 12SA7 which is listed on the schematics as 14Q7. So I am assuming that the voltages on the pins would be different on my unit.....sorry so dumb. :?

The 14v tubes are actually 12.6, voltages will be same. Loktals were assigned different numbers to distinguish from std 12v Octals.

The 6V Loktals were assigned 7v numbers, 35 & 50v tubes used same numbering as octals.

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Last edited by 35Z5 on May Fri 20, 2022 10:51 pm, edited 1 time in total.

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 Post subject: Re: Humming on AA5
PostPosted: May Fri 20, 2022 10:50 pm 
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Location: Mountains of Mourne. Ireland.
There is no 14Q7 tube on the model 1101 schematic.
Have you inadvertently downloaded the service data for 1100H which employs this tube.

Greg.


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 Post subject: Re: Humming on AA5
PostPosted: May Sat 21, 2022 3:01 pm 
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Location: Long Island NY
A heater to cathode short or leakage in one of the tubes will result in a 60-Hz hum. The fact that the hum goes up and down with the volume control strongly suggests that it is in the stages preceding the audio output. The rectifier and filter capacitors are probably fine. You say you tried running the set on DC, how was that accomplished? Unless you have 120 volts' worth of batteries or a very well filtered and isolated power supply, you would not necessarily eliminate enough ripple to change anything.

If it is heater/cathode leakage or a short in a tube, the most likely suspect would be the detector/1st audio tube. This is the 12SQ7 if you have the octal tube version of this set. (If you have the Loktal version then it would be a 14B6). You can try testing it if a tube tester is available, but not all testers are sensitive enough to detect this kind of problem. Swapping the tube with one known to be good is a better approach.

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 Post subject: Re: Humming on AA5
PostPosted: May Sat 21, 2022 5:52 pm 
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Location: Lexington, KY USA
The loktal tube pinouts are different from the octal equivalents, even if they are otherwise identical in function.

What sort of DC did you use for testing the radio?

Ted


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 Post subject: Re: Humming on AA5
PostPosted: May Sat 21, 2022 6:37 pm 
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Location: Long Island NY
Another thing to look at is the antenna connections. On radios of this type both wires to the loop have to be connected to their respective terminals, otherwise the front end of the radio is "running wild" and all sorts of hum and noise will be picked up, along with stations.

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 Post subject: Re: Humming on AA5
PostPosted: May Sat 21, 2022 7:01 pm 
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Check your work is Step #1. A reversed cap could be the problem. As mentioned by Greg, if that is the case, easy fix but the cap is toast.

Check that the negative leads of your new caps are isolated from the chassis. There is a terminal strip that is used for B- connections.

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 Post subject: Re: Humming on AA5
PostPosted: May Sat 21, 2022 7:49 pm 
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Location: SoCal, 91387
We always advise taking one or more pictures of the component side before doing surgery. The factory wiring routes and parts placement could then be followed, as they were designed to eliminate hum.

Lay the chassis on it's side or back, and turn it on. Put one hand in your lap, and using a non-metallic probe, such as a pencil or chopstick, try moving wires and your replacement caps slightly, to see if the hum is affected.

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 Post subject: Re: Humming on AA5
PostPosted: May Sun 22, 2022 2:07 pm 
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Attachment:
Kikasui Power Supply.jpg
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Chris/All
Thanks again for the valuable help. The DC I first used for test was just a 30 amp full wave cube I bought from Newark. However, I heeded your advice and used a Kikasui (excuse spelling) regulated unit and the hum disappeared, radio working good now. So, should I assume that it is the 35Z5GT rectifier or is it as you say, the 12SQ7 first audio..? BTW, one day I turned it over and was poking around (with pencil) to see if I could find the problem but nothing was apparent. Later that day, for some reason unknown, it started to work temporarily, the hum being only slightly detectable (no pun here)..... :)

Rich G


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 Post subject: Re: Humming on AA5
PostPosted: May Sun 22, 2022 4:35 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 5232
Location: Lexington, KY USA
The Newark thingy, whatever it is, may only produce rectified but unfiltered DC, which still has a large AC component. So most things that would cause hum on straight AC power would still cause hum. Though it might sound a little different.

If you still had a hum problem when running on smooth DC, the possible causes would be different.

So no, we don't really know enough to get much beyond guessing as to what's the problem. However, the temporary remission does point to an intermittent bad connection somewhere.

When it is humming, does the volume control turn it down completely, or just reduce the hum somewhat?

Can you measure the AC voltage on the filter capacitors? We may need to work on what sort of instrument you have to do this.

Ted


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 Post subject: Re: Humming on AA5
PostPosted: May Tue 31, 2022 10:33 pm 
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Hello All
I replaced the 12SQ7 but the unit continues to hum when running on AC. The hum stopes when running on regulated DC.
However, there are times when I turn on the unit and it works perfectly either on AC or DC. I tried poking around the wiring to try and expose the issues but no luck there.

The odd thing is that when it hums, I shut it off for the day and the next time I turn it on, it works perfectly on AC. Or, when it works perfectly, I shut it off, come back later and it hums. I have been very careful not to touch or disturb the unit in any way during these instances.....

rich g


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 Post subject: Re: Humming on AA5
PostPosted: Jun Wed 01, 2022 1:19 am 
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I bet there is a cold-soldered joint for one of the electrolytic capacitors. It is important to scrape clean the terminals & wires, "tin" the iron with solder, heat the joints and apply the solder to the joint so it flows smoothly. If you don't heat up the joint, you get a "cold-soldered" connection which becomes intermittent.


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 Post subject: Re: Humming on AA5
PostPosted: Jun Fri 10, 2022 9:25 pm 
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Attachment:
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Thanks for everyone's help, it's fixed and working fine. The problem was with the at the power tube for the output stage.

R Gillespie


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