On Wed, Mar 12, 2025 at 07:31 PM, DerekK wrote:
The issue is that the circuit I have is not bench performing the way one would expect. Thus I am wondering if it is possibly the mica caps that are use; though I have not heard of mica caps going bad as often as tantalum and electrolytics.
I do not remember ever hearing of mica caps going bad.? I do not think they age, or fail except by over-voltage stress.
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But one hears about electrolytics (both Al and Ta) aging and/or going bad all the time.? It seems to be in their nature.? Chemical reactions, and all that.
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Do you have a DC problem?? Might the circuit board need cleaning?
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I would like to know the real story about the LM121 - why they discontinued it, and why someone had the gall to re-use the part number.? If the chip itself disappeared from all production in the late 1970s, it is possible nobody ever made its SPICE model.? I do remember that AppNote (AN-79), but at the time I was much less interested in the use of chopper stabilized amps, so I probably gave little attention to the original LM121 series.
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Andy
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