For years I have struggled with the task of selecting transistor substitutes
with varying degrees of success. NTE/ECG is sometimes right but many times
they fail to perform anything like the original. What is a good way to
figure out which transistor *will* work without re-engineering the circuit?

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

On Sat, 19 Jun 2004 03:30:03 -0000, "Rich.Andrews"
wrote:

For years I have struggled with the task of selecting transistor substitutes
with varying degrees of success. NTE/ECG is sometimes right but many times
they fail to perform anything like the original. What is a good way to
figure out which transistor *will* work without re-engineering the circuit?

r

If you use an actual NTE/ECG match, it should work. People make the
mistake of thinking that all transistors with the same NTE/ECG match
are the same, and they aren't.

Tom

"Rich.Andrews" bravely wrote to "All" (19 Jun 04 03:30:03)
--- on the heady topic of "transistor substitutes"

Ri From: "Rich.Andrews"

Ri For years I have struggled with the task of selecting transistor
Ri substitutes with varying degrees of success. NTE/ECG is sometimes
Ri right but many times they fail to perform anything like the original.
Ri What is a good way to figure out which transistor *will* work without
Ri re-engineering the circuit?

The original transistor is often the best choice but sometimes it is
impossible to find or simply uneconomical. Substitution is sometimes
the only logical way to go and for this to be successful one has to
consider a number of factors.

The first thing to think about is that very often the original
transistor was either specially designed for the intended device or
sometimes the device was designed around an already available
transistor. Obviously the latter is the easier to substitute and the
first case is the more difficult.

- One important factor is to look for a transistor intended for a
specific task and a good example of this is a TV's Horizontal Output
Transistor. Thus one has to choose between a switching application or
a linear amplifier, perhaps an RF device, low noise preamp, etc.

- One has to match or exceed the original ratings for power, voltage,
current, gain, and speed.

- One has to decide if the new transistor will fit in the space occupied
by the original with the same pinout if possible.

Manufacters make it easy to select a sub by publishing tables of their
transistor specs sorted by their parameters. Motorola for example
offers programs which will try to match one of their transistors by
the parameters one enters as most important. Of course it tends to be
a more costly transistor but it gives a good idea what to look for.

A*s*i*m*o*v

.... When I was your age, we carved transistors out of wood.

Tom MacIntyre wrote in
news
On Sat, 19 Jun 2004 03:30:03 -0000, "Rich.Andrews"
wrote:

For years I have struggled with the task of selecting transistor
substitutes with varying degrees of success. NTE/ECG is sometimes right
but many times they fail to perform anything like the original. What is
a good way to figure out which transistor *will* work without
re-engineering the circuit?

r

If you use an actual NTE/ECG match, it should work. People make the
mistake of thinking that all transistors with the same NTE/ECG match
are the same, and they aren't.

Tom

I have tried the NTE/ECG approach and have had the least amount of success
with that. Small signal IF or RF transistors is what usually gives me
fits. Either it works marginally or doesn't work at all. Base current
requirements threw things off the last time. I will just keep plugging at
things until I get them figured out. The sheer number of choices make it
even tougher.

Thanks all!

r



--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.