I think a lot of it is down to how you were "brought up" with Electronics. I grew up with RA Penfold and I'm pretty sure my first electronics book wa= s=20 by an author called "Sparkes" but I'll have to dig it out to verify this.=20 BC5xx transistors were widely used in these books and magazine articles. I used to buy surplus bags of BC series transistors from a little model sho= p=20 in Mill Hill when we visited my Grandparents who lived there. That was just= =20 about the only opportunity I had of buying cheap electronic components as a= =20 kid as Tandy were too expensive. In fact ..... its only in the past few years that I've actually started=20 using PNP transistors as during my early years, my only exposure was to NPN= =20 devices lol. I'm nearly 40 now so this shows how far back I'm going ..... Dom ----- Original Message -----=20 From: "Philip Pemberton" To: "Microcontroller discussion list - Public." Sent: Friday, January 21, 2011 6:25 PM Subject: [EE] Jellybean transistors > Hi guys, > > At the risk of starting another holy war or Mass Thread of Off-Topicness > as I seem apt to do... > > I was recently chatting with a friend, and we got onto the subject of > 'jellybean' parts, via a discussion on the construction of read-write > amplifiers for disc drives (seriously!) > > Anyway. He proposed a current-mirror with two switches, good to 1MHz or > so, based on a bunch of 2N3904s. I commented "That's great, but I don't > have any 3904s, just a box full of BC547s and BC847s". To which he > replied "Are you serious? 3904s are jellybean NPNs and you don't even > have one of them?"... He proposed that I get a box of 2N3904s and > 2N3906s as a matter of some urgency... > > So I'm skimming the datasheets for the 3904 and the 547, and they don't > seem all that different.... > * Vceo is slightly better on the 547 (45V vs 40V) > * Vcbo is slightly worse on the 547 (50V vs 60V) > * Vebo is still the same old 6V on both > * Max collector current is worse on the 547 (100mA vs 200mA) > * Hfe is roughly the same, assuming we're talking about the B-spec > BC547 (aka BC547B) > * Slightly less input and output capacitance on the BC547 > * Better typical noise figure on the BC547 (2dB vs 5dB) > * They both have the same Ft (gain-bandwidth product) of 300MHz, > suggesting they'll both go to 100MHz if the current gain is kept below 3x > * Fairchild don't tell you as much about the 547 (no detailed on-off > characteristics, just a few vague graphs). No details on rise/fall time, > breakdown voltages or cutoff current. > * The pinouts are mirrored -- the 547 is C/B/E, the 3904 is E/B/C. So > you could put one in a socket intended for the other by rotating the > transistor 180 degrees... > > But other than that they seem to be basically the same thing by a > different name -- "a rose by any other name". Which brings me to my > questions: > > - Is there any point to getting some 3904s and 3906es? So far the > best reason I've got is "so I've got a few to play with" (which isn't > that good a reason). All my R. A. Penfold books call for the BC547 (or > one of its brethren), Horowitz & Hill demands the 3904. > - Are there any other jellybean parts I should look into keeping > around? I already have some BD139 and BD141 medium-power parts and a few > MJE3055 and MJE2955 TO220 high-power parts, and some 2N7000 MOSFETs, but > that's mostly it (aside from a few ST and IRF high-power FETs, and some > BF998 dual-gate MOSFETs and 2N3819 JFETs)... > > Thanks, > --=20 > Phil. > piclist@philpem.me.uk > http://www.philpem.me.uk/ > --=20 > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist >=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .