While replacing a 5.0uf electrolytic cap in a 1961 Japanese AM-FM-SW 7-tube hot-chassis radio I decided to measure and compare some of the specs of the four different 4.7uf caps I had in stock. The numbers varied more than I was expecting and choosing the best replacement became that much more difficult. Mind you, this was hardly an exhaustive test. I just wanted to see the relative merits of the four caps I had on hand so basically just measured the out-of-circuit capacitance and ESR values, as well as those of the original cap, at the five different frequencies offered by my DER EE DE-5000 LCR Meter. I know, the DE-5000 is not really a lab quality meter, but one does have to start somewhere.
All caps (except the original) are new and recently purchased. The original cap is a 5.0uf 50V electrolytic cap made by Japanese manufacturer National Radio and the four new ones are; a Topmay 4.7uf 50V cap; two MIEC 4.7uf caps (250V and 450V); and a Rubycon 4.7uf 450V cap. The Topmay was the cheapest and the MIECs the most expensive. Interestingly, however, the Topmay performed the best, especially at high frequencies, and the Rubycon the worst, despite the opposing opinions I sometimes see expressed by the electronics-cognoscenti in some of the online forums (see data in attached spreadsheet). The Rubycon was also the most unstable in that at 100 kHz its capacitance dropped and ESR rose noticeably during a single meter time-out cycle.
In the radio, this cap is placed in parallel with a 120pf cap between the cathode and plates of the 12AL5 FM Detector tube. I don't suppose the capacitance value is particularly critical here, I'm just curious as to the wide variance in readings picked up by my LCR meter and whether you think that any one of them would be better than the others in this location.
The radio was dead when I acquired it so I have no original symptoms to use for comparison.
So, based on the above data, which one of the five caps would you use in this radio?
Thanks.
All caps (except the original) are new and recently purchased. The original cap is a 5.0uf 50V electrolytic cap made by Japanese manufacturer National Radio and the four new ones are; a Topmay 4.7uf 50V cap; two MIEC 4.7uf caps (250V and 450V); and a Rubycon 4.7uf 450V cap. The Topmay was the cheapest and the MIECs the most expensive. Interestingly, however, the Topmay performed the best, especially at high frequencies, and the Rubycon the worst, despite the opposing opinions I sometimes see expressed by the electronics-cognoscenti in some of the online forums (see data in attached spreadsheet). The Rubycon was also the most unstable in that at 100 kHz its capacitance dropped and ESR rose noticeably during a single meter time-out cycle.
In the radio, this cap is placed in parallel with a 120pf cap between the cathode and plates of the 12AL5 FM Detector tube. I don't suppose the capacitance value is particularly critical here, I'm just curious as to the wide variance in readings picked up by my LCR meter and whether you think that any one of them would be better than the others in this location.
The radio was dead when I acquired it so I have no original symptoms to use for comparison.
So, based on the above data, which one of the five caps would you use in this radio?
Thanks.
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