This has me puzzled (resistor change)

tubeguy · 2019-01-20T22:33:41+00:00

There is a video on youtube, where a guy re-caps and repairs and tests out a late 1940's Precision Apparatus E-200 signal generator. Video name: "Repair of a late-'40's Precision E-200-C RF signal generator" This sig gen has a built in audio tone modulator (oscillator). He replaced a resistor in that circuit, which was out of tolerance. He replaced it with a modern film type resistor. The audio modulation did not work afterwards. After testing everything, he went and replaced that resistor (again) with an old style carbon resisstor, and after that, the modulation worked. What the heck????? I was always under the impression that film resistors are identical (electrically), and their only difference is appearance. Now I learn that is not true..... WHY?????

Jan 20, 2019 23 Replies

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Phil Allison 7 years ago

** If you find an electro well above its marked capacitance value - what do you conclude ??

... Phil

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Sjouke Burry 7 years ago

That the oxide layer has degraded, and might be about to fail?

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John-Del 7 years ago

Back when I used to carry a big box of tubes (valves) for on site repair, I could spot any tube out of hundreds in seconds. After a long time using them, we don't "read" the tube number as much as just flat out recognize it - just like when reading words.

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Phil Allison 7 years ago

** How do you check for this?

..... Phil

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