An Introduction and a Philco 90 issue.
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Got it! When I reattached one of the Bakelite blocks I rebuilt to the chassis, I pinched some bare transistor leads going to the socket you said was shorted under the nut. Corrected it and the radio started working. Unfortunately, the only electrolytics I have include the one that vented badly the last time I powered it up so it started steaming about a minute after the radio began playing. No problem...I have 10uf 450V Nichicon caps coming in a day or two. I had my multimeter attached to the BC resistor terminal one and I was measuring volts and there was no more bouncing around and no burning. Next step, install the new filter caps when they come and then I'm going to rebuild the 2 capacitor cans, 30 and 24. Right now I just have film caps tacked in. Steve, your help is so appreciated. I'm sure I'll be back with more help needed requests!
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Very good!
You will also want to replace those caps in the tone control. If one of them becomes shorted, it will take out the output transformer or the filter choke. Good luck with your project.
Steve
M R Radios C M Tubes
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I will...and in my previous post I meant to say resistor...not transistor. No transistors in 1932 Philcos!
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I finished the recap and rebuilt the electrolytic cans with the 12uf Nichicon electrolytic caps and did the alignment and the radio sounds fantastic. Then I moved the chassis upstairs from my basement shop and installed it in the cabinet. When I turned it on, it had the same sensitivity and volume but there was a faint but audible low level hum that was constant if the radio was playing broadcast AM or if the Bluetooth was playing clean music from my cellphone. The radio is on an extension cord but other than that, the setup is the same. The basement shop is full of fluorescent lights and potential interference producing electronics and the radio played clean. Any suggestions as to where I can begin troubleshooting?
(This post was last modified: 12-06-2021, 12:56 PM by cknob.)
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The hum is probably normal. I just fired up a Crosley 66TC yesterday and it had a PS hum, constant, but not noticeable over any level of audio except almost-off.
I would not mess with it. They did as good as they could with low value caps and that is the historic result. Anything less would be modified.
It has other audio issues. Ron has discussed them a lot and a change to the detector you could also do, but I would not.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
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My question is why now...all I did was move it from downstairs to upstairs and this hum appears. Maybe it was there and I couldn't hear it until I installed it in the big cabinet and then it began to resonate? This isn't the cathedral set...it's the lowboy and stands about 4 feet high.
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The speaker "in the cabinet" is going to produce better bass response, particularly directly in front of the cabinet.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
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What does the "PS" in PS hum mean? Power source?
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Power supply.
Russ is 100% correct - your radio's speaker will always sound better in the cabinet, and then you will notice more bass response and, consequently, more hum.
As Russ said, if you only notice hum with the volume all the way down but do not notice it otherwise, ignore it as this is the best it can be.
--
Ron Ramirez
Ferdinand IN
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As Ron said, this is probably as low as the hum gets. I have the same 90 lowboy and there is always a slight hum in the background.
Most likely the inherent background hum is caused by the directly heated filament in the output tube. Regardless of whether you have the model with the PP 45 tubes or the PP or single 47's, they both have the same type of filament heated by AC. The reversing polarity AC filament voltage modulates the bias voltage between the filament and control grid, effectively adding a slight hum signal to the input.
Ideally, if everything is perfectly balanced, the hum should cancel, but rarely is this the case. Radios like the 37-116 with directly heated triode outputs have a hum balance pot to null out the filament induced hum. It's the worst with a single 47 because there is some hum cancellation with a push pull output stage. Also the 47 is a more sensitive tube than the 45 as it requires much less input signal for the same output, so the filament hum will be more noticeable.
The ultimate solution was the introduction of indirectly heated cathode tubes like the 59, 42 and 2A5. Radios with these tubes do not suffer from this effect and have a lower inherent hum level.
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Got it...sounds like I've gotten it as good as it's gonna get. Thanks for all the help guys.
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You might want to try plugging into an outlet on a different circuit in your house. Ive found that some of my home's circuits are noisier than others. Some folks are able to track down the source of the noises in their homes, but Ive never been able to do that with complete success. What I do now is to use a "central" (known to be quiet) outlet when playing my radios.
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Quite often the source of noise will be a computer and/or monitor or a wall wort. Computer equipment and TVs will generate noise just plugged in the wall.
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