Marshon wrote:
Hi guys,

Throw me a bone here.......
Although I only have my UK Foundation licence, I'm not quite a novice
when it comes to circuits. I worked for many years as an IT systems
engineer, can read a schematic, and understand what a circuit is
doing.
What is really starting to bug me is trying to locate a source of
information for alternative parts, especially transistors. I have
acumulated literally hundreds of parts, but I can guarantee that for
any given project I wont have the exact quoted part and will have to
order in a part costing pennies with handling and delivery in pounds.
Maddening to be sure.
Does anyone know of a site that gives a list of alternative or
equivalent parts? As an example, I have hundreds of 2N2222 transistors
but the requirement is for a single BC547 of which I have none. The
datasheets would suggest that the 2N2222 would do the job, but is it
always going to be a 'suck it and see'?

Any advice gratefully received.

Simon (MW3CUR)
When looking at transistors to see if one on hand would be a suitable
sub for one called for in a design the important paramters are the
max voltage ratings (VCBO, VEBO and VCEO), the current gain (Hfe) and
the transfer or cutoff frequency Ft ratings. If the device must handle
any power then look at the power dissipation rating (PD) and max current
ratings (Ic). Be aware that some ratings such as Hfe and Ft are
made under certain operating conditions, IE: a transistor could have a
low current gain at low collector current, but a moderate to high gain
at high currents. That's great for a power amp, but not so good for a
small signal amplifier. If you have a curve tracer (Heath IT-1121 is a
nice inexpensive unit that shows up on ebay from time to time, you need
an external scope for this one) you can identify unknown transistors.