From a FB group Building Transistor Radios
Markku Vuorensivu
Tell me more! I’m all ears!
I got a thousand 2N3904 BJTs from Mouser, and ten packs of 100 from eBay. I selected a dozen from each and measured their current gain using two methods: a cheap DMM, and a ‘transistor tester’ which has the ZIF socket and the OLED display.
The specs for the hFE say 100 to 300, and the ones from Mouser are all grouped around 200, right in the middle of the range. The ones from eBay are all over 300, typically 320 to 360. That’s more than the specs and out of range. I haven’t measured any other parameter, except for Vf, which was around 0.69V for the Mousers and around 0.63 volts for the eBay. I think the 0.69V is high for any silicon transistor, but within specs.
I have read that BJTs are made with a series of compromises. If one parameter is maximized, some others may be compromised. If that’s true, the eBays with higher gain may have some other parameters that have been compromised. I won’t know until I do tests. One thing I thought about doing is make a jig with a socket and coil and capacitors to make a Colpitts oscillator that oscillates at 300 or more MHz, to see how high the BJTs will oscillate. They should be able to do 350 MHz or maybe more, up to 400 or 500 MHz. 😁
2018-06-21 More from FB
Dror Gluska
I bought a thousand 2N3904 transistors from Mouser, and ten packs of 100 from a China seller on eBay. A dozen of the Mousers current gain, specified between 100 and 300, were all around 200. A dozen of the Chinese ones measured around 330 to 360, which is too high. That may sound like it’s good, but transistor chip making involves compromises. If there is one of the specifications that’s out of spec, there is usually other specs that are compromised.
Yes, the Chinese ones were a bit cheaper than the Mousers, but I prefer the legit parts from Mouser.
Also, all of the through hole parts are getting more difficult to obtain. The industry has converted to surface mount parts and someday that’s all that you’ll be able to get from legit companies like Mouser. The only places that will still sell through hole parts will be overseas.
