I found an Astable multivibrator schematic online and the transistor they used was a NPN 2n2222 and I didn't have one so I was just wondering if it's a must to use a specific NPN or PNP for circuits or can they all work if the transistor has a close enough current gain and power output .

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    \$\begingroup\$ You've provided no reference schematic. But chances are that you can use a wide variety of BJTs. If it doesn't work, get back to us about what you actually tried to do and we may be able to help. \$\endgroup\$ – jonk Dec 19 '18 at 19:10
  • \$\begingroup\$ yes, as along as the specs match or are even close it should work just fine, edge cases aside. \$\endgroup\$ – dandavis Dec 19 '18 at 19:29
  • \$\begingroup\$ A 2N2222 is a general-purpose silicon NPN transistor. You could probably use any smallish silicon NPN in there, and it's a near certainty that another general-purpose one would work. You do need to substitute NPN for NPN and PNP for PNP -- mixing those won't lead to joy. \$\endgroup\$ – TimWescott Dec 19 '18 at 20:04
  • \$\begingroup\$ Some transistors have lower Cob (capacitance from output-to-base (also known as collector-to-base) and thus provide more isolation between input and output. And also, what with Miller Effect usually a big consumer of input signal energy, allow better use of precious signal power. We tend to call those transistors "RF transistors". If the transistors have specially wide regions between the base-bond-wire and the base region between collector and emitter, so the base charges can be QUICKLY removed, the Boltsmann (thermal, KT) noise tends to be lower, and we call those "low noise" transistors. \$\endgroup\$ – analogsystemsrf Dec 20 '18 at 4:48

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