2N3055-2N2955 or C5200-A1943 or TIP41-TIP42 better to use in audio amplifier?
2N3055/2N2955: Reliable work-horses, cheap and abundant. Very little spec. Runs out of hFE quite soon as IC increases. You never know what is in the can, the spec is so loose (not rip-off).
TIP41/TIP42: Nice delicate little 'power' transistor. Current gain drops off quite quickly. Don't mess with the boys in the TIP range just go for the TIP35C/TIP36C. They are about the same price, but even the TIP35C/TIP36C are delicate and not well speced. TIP3055/TIP2955 more rugged.
C5200/A1943:
Now you are talking. Good for 5A maximum in your application when you take into account the SOAR and current gain graphs, so you would need least 4 in parallel. These are probably based on the Toshiba originals. It was a sad day in the audio field when Tosh stopped making audio power transistors.
Here is a recommended procedure for choosing audio power transistors:.
(1) Check if there is a compliment to the transistor. In fact, there is no such thing as a complement; it's an allusion. By definition the two types are made differently using different materials. Normally the NPN version has the better characteristics but not always. With MOSFETs the situation is not so definite. It's not unusual for so called complementary pairs to have radically different specifications.
(2) Google to see if it both NPN and PNP (N type and P) types, are available at a price you are prepared to pay.
(3) Google for any problems with either NPN or PNP versions Ask around.
(4) Check that the manufacturer is continuing to make the device, or is it on 'one-time-buy' notice or 'not recommended for new design' notice or even obsolete.
(5) Does the data sheet say that the transistor is intended for high quality audio. Alternatively is it used in any top end gear or mentioned on audio sites as being good, diyaudio for example. Do any of the text books say it is good?
(6) Check maxim current required. In your case 18A
(7) Check that VCE is it at least 2x the voltage of the power lines of your propose amp plus 10V minimum. In your case, assuming +- 75V rails, you get (75 *2)+10 = 160V
(8) Check the hFE linearity against IC, the flatter the better for two reasons: low distortion and ease of driving especially at 40KHz. Most power transistors suffer from hFE drop-off as IC increase, often severely, same for low currents which is right in the croos-over region on class AB amps. The 2N3055 suffers badly from hFE droop for example, and who knows what happens at low currents.
(9) Check the SOAR graph. To an approximation VC= one supply line/2. IC = max output current/2. In your case VC= 75/2=37.5V and IC =18/2=9A.
Those are the basics more or less in the correct order.
Once you have focused on a complimentary pair of power transistors:
(10) Check the FT: 30MHz or over should be OK.
(11) Check capacitances, the lower the better. MOSFETs have massive capacitances, 1.5 nF for example. And the capacitance changes acording to VC and IC so thy cause distortion and make life difficult in many ways.
(12) Check thermal resistance junction to case and case to heat sink
(13) Do the thermal budget to find out what size heat sink will be required
(14) Have a beer
(15) Start looking at the spec details
This may sound like an awful rigmarole, but once you have done it a few times, it isn't that bad and doesn't take too long either. In fact you should carry out the same procedure for every component you design in. Of course, the parameters to check would be different.
Notes:
(1) Because of the undesirable characteristics of power transistors, it is best to stay with an emitter-follower (source- followwer) configuration.
(2) The hFE and VEB of the complementary pair you actually use need to be matched to obtain low distortion.
After all that a bit of light relief:
**broken link removed**
Data Sheets
2N3055_MJ2955 (2N2955) (NPN_PNP)
https://www.onsemi.com/pub_link/Collateral/2N3055-D.PDF
TIP41 (NPN)
https://www.fairchildsemi.com/datasheets/TI/TIP41C.pdf
TIP42 (PNP)
https://www.fairchildsemi.com/datasheets/TI/TIP42.pdf
2SC5200_FJL4315 (NPN)
https://www.fairchildsemi.com/datasheets/2S/2SC5200.pdf
2SA1943_FJL4215 (PNP)
https://www.fairchildsemi.com/datasheets/2S/2SA1943.pdf