Rudge wrote:
"Eeyore" wrote in message
...

Rudge wrote:

I need a T039 NPN transistor with an 80 volt BVceo rating such as a
BC142.
My nearest stockist holds the BC141 which has a BVceo rating of 60volt.

If I buy a BC141 and test the breakdown voltage, what are the chances
that
it will exceed 80volt?
No idea, but specific devices are indeed selected by parameters from a
general
device group by testing, so you're in with a chance.

If the yield at higher voltages was good for that batch, you may well find
that
the '141 may meet a '142 spec.

What application is it used in btw ?

Graham

I want an NPN T039 or T05 driver transistor for use in an audio amplifier.
The supply rail is 75volt. Quiesent current is about 10ma I think. 1 Watt
dissipation at 25 C. The original was an RCA 39252 (which I have no data on)
or a 2N2102. They may have been selected to to work at 75volt.

Many thanks,
Rudge


You need to give more details on the circuit. If this is the first
stage of the amplifier, it's a lot easier than if it's the "driver"
for the output stage.
If this thing goes between ground and 75V, you want WAY more than an 80V
transistor.
If it goes between +-75V, you need way more than a 150V transistor.
Unless this is a special transistor, you can't expect to get anywhere
the maximum power dissipation at anywhere near the breakdown voltage.
Take a serious look at the dynamic characteristics, peak voltages
and currents driving the capacitive load and the secondary
breakdown curves. The RCA Power Circuits manual SP-51 has
a whole chapter on this.

And worry about the power numbers too. That 25C number is a metric
that gives you some idea about what's going on. What you really
care about is the die temperature. And it's WAY more than ambient
in a small package like that.
mike

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