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Stromberg Carlson 1500 Squeal - Printable Version

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RE: Stromberg Carlson 1500 Squeal - David - 10-12-2026

You have 2 caps in the bottom left corner area look to be a 502k an 473k might try moving them away from the chassie just a little. Please be careful using the selenium if it blows the stink!! David

RE: Stromberg Carlson 1500 Squeal - dconant - 10-13-2026

Thanks for the input David. I moved the caps and it made no difference. Also I only had the selenium in just for a test. The 1N4007 is connected again.

I still need to find the foil side of the caps MrFixr55 mentioned. I have a new scope (Rigol DS1202ZE) I am trying to figure out how to use. Way more scope than I needed.

Dan

RE: Stromberg Carlson 1500 Squeal - RodB - 10-13-2026

That scope takes a little to learn but you'll love it. Just like getting a new car you've always wanted.

RE: Stromberg Carlson 1500 Squeal - dconant - 10-13-2026

I would be most grateful if someone could tell me exactly how to connect and set the settings on my Rigol 1202ZE to this radio so I can read the power supply. This is just so I can get some kind of reading on the scope and help me learn how to use the scope.

RE: Stromberg Carlson 1500 Squeal - Jimradio - 10-14-2026

dconant, I have this radio on my bench, just found the schematic, have not done anything to it yet. I will keep an eye on your post.

RE: Stromberg Carlson 1500 Squeal - dconant - 10-14-2026

Jim, Hopefully you don't run into my problem.

Dan

RE: Stromberg Carlson 1500 Squeal - dconant - 10-14-2026

Since I could not find a reliable way to determine the outside foil of the caps I decided to swap the caps around one at a time. There was no change at all. What I have noticed now is when I take the radio upstairs I get a few more stations and they don't have the squeal. It is just one spot on the dial with the squeal. So I'm thinking it is something in the house interacting with that station. If you guys agree I am going to call this one done.

I did not like the 13 volts showing on the first 12BA6 so I removed the CL90 and replaced it with a 120 ohm 5 watt resistor. All the 12 volt tubes now run about 11.6 volts.

RE: Stromberg Carlson 1500 Squeal - Arran - 10-15-2026

I did not think that noting an "outside foil" would make any difference, mainly because poly-film caps don't really have a foil, it's a metallic deposit on two sides of a strip of plastic film. Even on the old style paper caps the manufacturers themselves didn't pay any attention to it, and those actually do have two strips of foil in them. I believe the section of the radio where this may have made a difference was in the audio section, but there they are basically passing AC, and blocking DC, but that would show up as a hum in the audio. The test I have seen in some videos was to connect a cap to a scope probe whilst holding onto the body of the cap, the trouble with this is that your body is acting as a wide band antenna, and your fingers are coupling directly to the outside of the cap, this is like grabbing the loop antenna of your radio with your fingers, the stations often get louder, if the caps are routed properly then they shouldn't have anything coupling to them other then what they are connected to.
The problem with the CL 90 is that it is too large, the 90 stands for 90 volts, so there is a 90 volt drop when they are cold, giving the tubes a chance to heat up. I've normally heard of people using these in series string TV's with a tube chassis, but those often have multiple strings of tubes in series, and they can be 300-400 ma in each string, and apparently they were not intended to work with loads under 500 ma. The string of your Stromberg is 150 ma, plus whatever the B+ is, so maybe 250 ma max. I do not think this has anything to do with the squeal, or lack of gain, I would suspect an open or drifted silver mica cap in one or more of the IF cans, this is a more common problem then the SMD/silver migration one.
Regards
Arran
https://antiqueradios.com/forums/viewtopic.php?t=165042

RE: Stromberg Carlson 1500 Squeal - dconant - 10-16-2026

Thank you Arran. I learned something from your statements about the CL90. The CL90 I put in has been removed and replaced with a 120 5 watt resistor. Voltages are almost the same on the 12 volt tubes (11.5 +-). Trying to measure where the outside might be is pretty hard to do as the harder you grasp the more deflection you get. That is why I did the end to end change on my caps. I did not consider caps in the IF cans. Since the schematic does not list them I would not know what to use. I had Zenith that was not marked but someone suggested 110pf (I think). So I'll open up one and have a go at it.

Dan

RE: Stromberg Carlson 1500 Squeal - dconant - 10-16-2026

Here is a picture of one of the IF cans. I assume the caps are under the wafers near the pins and that I would have to drill out the collar to get at the caps. I also assume at this point there is no going back and I will have to replace the wafers with the appropriate silver mica cap. The big question is what value do I use?

   

RE: Stromberg Carlson 1500 Squeal - Arran - 10-16-2026

I would consult Shango066's channel on Y.T, he has multiple videos where he replaces the caps inside the cans, now he usually uses one of those cheap component testers to measure the values. As you surmised the caps are sandwiched in the base of the assembly that is held together by the brass eyelet. They are not all the same value, which is why they should be measured, if you are lucky you may find a posting somewhere by someone who has already restored one of these sets, but there is no guarantee that yours will be the same, but likely more on point then chucking 110 pf caps at everything. As I mentioned, if you tried aligning the IFs and still had poor gain, open mica caps is likely a cause, the mechanical connection between the silver deposits and the outside world is not exactly the best, plus it can tarnish. Some people have actually fixed these by dropping the sheets in Tarnex (silver polish) but with NP0/C0G caps available, and inexpensive, I think you would have to be desperate to do it.
Regards
Arran

RE: Stromberg Carlson 1500 Squeal - dconant - 10-20-2026

I took the radio to a friends house and tried it out. First thing right off the bat the pilot light blew. Voltage higher over there. It will stay blewed Icon_lol . There was no squeal and I got less noise. So this confirms something in my house is the culprit.

RE: Stromberg Carlson 1500 Squeal - Joe Rossi - 10-20-2026

I would never have thought of making a field trip!  Good work,  Joe

RE: Stromberg Carlson 1500 Squeal - Jimradio - 10-21-2026

Yes, I have a flat screen tv with cable box in my work room sometimes I have to unplug it because it interferes with the radio. Our washing machine used to cause noise until the manufacturer sent me a filter to install in the washer. Anything with a transformer can raise havoc.

RE: Stromberg Carlson 1500 Squeal - dconant - 10-21-2026

Seems like it is more bother than it is worth with some of these radios when you have to go around and unplug everything so you can listen to the radio. All my AA5/6 radios suffer the noise problem probably because I am so far away from stations.