Simple Microphony sensor for valves (tubes)

[Jon Snell]

Don't caps and transistors make noise when you tap on them ?

Capacitors can, depending on their placement and type, transistors are generally quiet unless damaged.

[Enzo]

Caps can be noisy like that but mostly not. I'd say ceramic disc caps are most likely to get that way, but not always certainly. And if a disc were one of the feedback caps in a trem oscillator, who cares if it is a little microphonic? Semiconductors? I am surprised if I run into one of those that react to mechanical.

[Leo_Gnardo]

Don't caps and transistors make noise when you tap on them ?

Disc caps, definitely. Especially cheap old ones. Larger values, too, say the .01 to .1 uF you find in funky old amps & even Fenders in the 60's & 70's. Film caps, if there's enough gain in following stages you'll hear them respond if tapped with a hard probe like screwdriver tip. Transistors? So rare I've seen/heard it only a handful of times. More like half a handful, 3 or so in 50+ years.

[vintagekiki]

Preamp Tube Tester and Power Amp Driver
http://priceamp.dotster.com/diypreamp.htm
Schematic
Concept