Hi All,
I am having difficulty sourcing the above transistor types for an audio project, can anyone please advise on suitable alternatives ?
The devices are specified for both input and intermediate (vas) stages - and are also used in constant current source applications - all within the same project diagram.
Any advice would be hugely appreciated.
I am currently considering using 5401 / 5551, would these be suitable replacements generally ?
Thanks in advance
I am having difficulty sourcing the above transistor types for an audio project, can anyone please advise on suitable alternatives ?The devices are specified for both input and intermediate (vas) stages - and are also used in constant current source applications - all within the same project diagram.
Any advice would be hugely appreciated.
I am currently considering using 5401 / 5551, would these be suitable replacements generally ?
Thanks in advance
On semi MPSA06/56 can have generous gain, specified at 100.
generic 2n5401/5551 can be more pedestrian, specified at 50. Few circuits will require the extreme gain levels.
5401/5551 have more voltage standoff capability, which circuits requiring MPSA06/56 won't need. Possibly slightly noisier.
BC556 (pnp) and BC546 (npn) are pretty close, having vceo 65 instead of 80. But you have to put them in backwards, they go cbe left to right with the flat pointing at you instead of ebc like the ON MPSA06/56. The gain is 110 for the A suffix and more for B & C .
generic 2n5401/5551 can be more pedestrian, specified at 50. Few circuits will require the extreme gain levels.
5401/5551 have more voltage standoff capability, which circuits requiring MPSA06/56 won't need. Possibly slightly noisier.
BC556 (pnp) and BC546 (npn) are pretty close, having vceo 65 instead of 80. But you have to put them in backwards, they go cbe left to right with the flat pointing at you instead of ebc like the ON MPSA06/56. The gain is 110 for the A suffix and more for B & C .
What voltage rails are we talking about?
My general purpose transistors are BC546/556 for rails up to +/- 55V and 2N5401/5551 up to +/-75V
Above that, classic MPSA42/92 .
And why not just stock the higher voltage ones and use them everywhere?
Because each voltage jump is paid for with worsening properties (nothing is "free") as in much reduced Hfe in each case so it´s better to use the one which actually matches needs and not uselessly overkill.
My general purpose transistors are BC546/556 for rails up to +/- 55V and 2N5401/5551 up to +/-75V
Above that, classic MPSA42/92 .
And why not just stock the higher voltage ones and use them everywhere?
Because each voltage jump is paid for with worsening properties (nothing is "free") as in much reduced Hfe in each case so it´s better to use the one which actually matches needs and not uselessly overkill.
Thanks, indianajo !
That helps a lot, I see that RS has hundreds of them at reasonable pricing - and I suppose that being rated at only 100 mA as opposed to the 500 to 600mA of the MPSA types should cause no difficulties .... but I'm thinking that Ic of 100 mA may be a little low for the VAS ?
That helps a lot, I see that RS has hundreds of them at reasonable pricing - and I suppose that being rated at only 100 mA as opposed to the 500 to 600mA of the MPSA types should cause no difficulties .... but I'm thinking that Ic of 100 mA may be a little low for the VAS ?
Gerry, have you tried Communica? Their site lists both the 06 and 56:
Bipolar Junction Transistor [MPSA56] .::. Communica Online
Bipolar Junction Transistor [MPSA06] .::. Communica Online
Not sure what their stock levels are though, might be worth giving them a call.
Bipolar Junction Transistor [MPSA56] .::. Communica Online
Bipolar Junction Transistor [MPSA06] .::. Communica Online
Not sure what their stock levels are though, might be worth giving them a call.
As these are in TO-92 package, with VAS voltages around, anything more than about 5mA will be meltdown
Yes.
TO92 is ample for input pair duty but VAS can dissipateb substanjtial power.
And even if, say, being rated 500 or 600mW then dissipating 300mW "is" within rating, remember that´s at 25C ambient temperature, not guaranteed at all inside a power amp chassis, and to boot they are not happy working hot (even if not dying) so I also suggest TO139 or TO220 cases for VAS duty.
TO5 sits halfway but is not very standard or popular any more.
TO92 is ample for input pair duty but VAS can dissipateb substanjtial power.
And even if, say, being rated 500 or 600mW then dissipating 300mW "is" within rating, remember that´s at 25C ambient temperature, not guaranteed at all inside a power amp chassis, and to boot they are not happy working hot (even if not dying) so I also suggest TO139 or TO220 cases for VAS duty.
TO5 sits halfway but is not very standard or popular any more.
Slightly larger packages are a good idea and a convenient step between teensy T092 and heatsink models like TO212, TO126 or fullpack versions. Typical medium power transistors slow the VAS down and increase distortion with their large amounts of capacitance but you can rate most TO92L package devices such as 2SD667/B647 at twice the TO92 power rating and that's often enough for 70W/8R. There are even better TO92L types (lower Cob) again for the VAS but I'm sure you can search them out and even the cheap copies I've listed here work quite well.
You can have a much cooler running VAS with 2SD669/B649 or H669/H649 which are similar devices in a larger TO126 size package. Note the pinout of Japanese types including TO92L, is ECB - same as TO220 and reverse of TO126, looking at the label faces with pins toward you.
You can have a much cooler running VAS with 2SD669/B649 or H669/H649 which are similar devices in a larger TO126 size package. Note the pinout of Japanese types including TO92L, is ECB - same as TO220 and reverse of TO126, looking at the label faces with pins toward you.