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I am having a problem making electrets work in various circuits I’ve taken from Charles Platt”s “Make: More Electronics,” 2016. The simplest is on page 59. It connects an electret to ground on a breadboard, and also to a 4.7K resistor. The latter is attached to the positive bus. I then measure AC volts between ground and a point between the electret and the resistor. I first tried using this brand: HiLetgo 10pcs Electret Condenser Microphone 52dB MP3 Microphone Accessories 6x2.2mm, which I got from Amazon. The first of these electrets worked the first couple of times I spoke aloud to test it, then didn’t work. The next couple of electrets were the same, so I sent them all back. I then got, also from Amazon, this brand: BOJACK 9767 Cylindrical Electret Microphone 2 Pins 9.7 x 6.7 mm Microphone for Intelligent Robot (Pack of 10 Pcs), which hasn’t worked at all. The book says to measure AC voltage both before, and while, speaking aloud. I should register, the book says, .1 (point one) millivolts before speaking and 10-20 mV while speaking. I have gotten a stable reading (about 5 mV with the first brand and 9 mV with the second) before speaking. With the first brand I got a higher reading when I spoke, but the readout varied quickly. I think it was maybe 2-3 volts. With the second brand I get no increase at all. It seems doubtful that both brands would be defective and, rather, that I’m somehow getting the procedure wrong. I’d be grateful for any opinions.

You have the datasheet for the electret(s) that you use? Some are very basic, some include an opAmp IC built in, some operates at 1.5V, other at 10V, so they don't all behave the same.

Without seeing the datasheet, I would presume that your circuit killed the component(s) from over power (voltage time amperage) consideration, or by destruction of the capacitor internal insulation.

Thank you for your response.