catman Posted October 22, 2019 Share Posted October 22, 2019 (edited) G'day all, again this is not strictly 'hi fi' but it is interesting to me regarding capacitor behaviour. I was getting some reports of hum on one of my Ham Radio transmitters through my DIY microphone preamplifier. Someone suggested putting a capacitor across the supply rail, which I eventually tried. I found a large 2200 uf 50 v electrolytic capacitor in my components parts box, and tried that in the circuit and immediately noticed significant hum reduction, so I properly soldered it in and left it powered up whilst I did something else for an hour or so. I came back a couple of hours later and checked the transmitter audio again and I was stunned to observe that all hum had 'gone'! Did that large electrolytic capacitor need some time to properly 'form' and work optimally? Apparently so! Regards, Felix. Edited October 22, 2019 by catman Spelling. Link to comment Share on other sites More sharing options...
F18 Posted October 22, 2019 Share Posted October 22, 2019 Ideally old capacitors should be reformed in conjunction with a circuit and variac before using. Apply voltages by steps. 1 Link to comment Share on other sites More sharing options...
Monkeyboi Posted October 25, 2019 Share Posted October 25, 2019 It depends. I have some Elna 2500uF 25V axial leaded capacitors that were purchased in the 1970s that tested okay on the LCR meter for capacitance, ESR and leakage. However as @F18 said, it's good practice to "reform" them prior to placing them into service. My method to reform aluminium electrolytics is to wire in a series resistor and slowly raise the d.c. voltage to the full rated operating voltage for the cap whilst monitoring the leakage current through the capacitor and the voltage across it. If all goes well, I repeatedly discharge the capacitor to remove any residual charge and then retest it on the LCR meter, once again for capacitance, ESR and leakage. These steps are by far a better approach than installing an old aluminium electrolytic of unknown condition and risking it leak or vent the remaining electrolyte throughout the equipment or worse still explode! As for the reduction in hum level after one hour of in-circuit use. Yes it is possible the capacitor did some additional reforming from the supply voltage whilst in use. Anyhow, it looks like you solved the hum problem which pretty well much was the objective of the exercise. Cheers, Alan R. Link to comment Share on other sites More sharing options...
Decky Posted November 7, 2019 Share Posted November 7, 2019 No. Fake news. 2 1 Link to comment Share on other sites More sharing options...
Guest scumbag Posted November 10, 2019 Share Posted November 10, 2019 On 08/11/2019 at 9:41 AM, Decky said: No. Fake news. It sounds like you're turning into the Donald Trump of Stereonet. Link to comment Share on other sites More sharing options...
Decky Posted November 10, 2019 Share Posted November 10, 2019 19 hours ago, scumbag said: It sounds like you're turning into the Donald Trump of Stereonet. Funny that you say that, since I always perceived these quasi-scientific auiophiliac fantasies that are so often propagated on SNA as being very much aligned with Trump's evangelical capitalism creed. There must be something there - we just need to find some radical left axes of evil and we can wait for a multi-channel Armageddon - we just need to remember to use at list 4 stage ADC and DAC conversion just to record the whole event on a cassette tape and enjoy it fully. Link to comment Share on other sites More sharing options...
Wozza_Lee Posted November 11, 2019 Share Posted November 11, 2019 It sounds like you're turning into the Donald Trump of Stereonet. Ooofff..... That's a rough thing to say.I mean I don't know the man but he can't be that bad Link to comment Share on other sites More sharing options...
Guest scumbag Posted November 11, 2019 Share Posted November 11, 2019 10 hours ago, Decky said: Funny that you say that, since I always perceived these quasi-scientific auiophiliac fantasies that are so often propagated on SNA as being very much aligned with Trump's evangelical capitalism creed. There must be something there - we just need to find some radical left axes of evil and we can wait for a multi-channel Armageddon - we just need to remember to use at list 4 stage ADC and DAC conversion just to record the whole event on a cassette tape and enjoy it fully. Word vomit. Link to comment Share on other sites More sharing options...
Uncle Seth Posted November 11, 2019 Share Posted November 11, 2019 43 minutes ago, Wozza_Lee said: Ooofff..... That's a rough thing to say. I mean I don't know the man but he can't be that bad I believe it's entirely possible that Trump is worse than people are aware, and by extension... @Decky, this is not the only source that I have heard quote similar properties of capacitors. What do I know? I'm a scientist. Link to comment Share on other sites More sharing options...
Wozza_Lee Posted November 11, 2019 Share Posted November 11, 2019 It was a reference to decky. Not trump, he is actually the worst Link to comment Share on other sites More sharing options...
Monkeyboi Posted January 5, 2020 Share Posted January 5, 2020 On 08/11/2019 at 7:41 AM, Decky said: No. Fake news. Fake news? How so Decky? Care to enlighten us all with your pearls of wisdom as the rationale that aluminium electrolytic capacitors can't or should not be reformed in the context of @catman's post? Link to comment Share on other sites More sharing options...
Decky Posted January 5, 2020 Share Posted January 5, 2020 1 hour ago, Monkeyboi said: Fake news? How so Decky? Care to enlighten us all with your pearls of wisdom as the rationale that aluminium electrolytic capacitors can't or should not be reformed in the context of @catman's post? Do not take life so seriously. Link to comment Share on other sites More sharing options...
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