Connect it exactly the same as you would an NPN, but reverse the
polarity of the power supply voltage. If there's a bias circuit using a
diode, the diode (and bias supply polarity, if it's a separate supply)
should also be reversed.

If it's necessary for you to use the PNP with a positive supply voltage,
it's still possible, but it complicates the circuit, and adequate
bypassing becomes essential and sometimes difficult. In that case, a
diagram (and preferably a layout) of a known working circuit is desirable.

All other things being equal, a PNP generally has lower ft and higher
capacitance than an NPN, which is probably why they're less commonly
used. This difference is due to the basic physics of the device (lower
mobility of the carriers, as I recall).

Roy Lewallen, W7EL

PaoloC wrote:
Hi,
I feel a little lazy today, and Mr. Google didn't return anything useful
to my searches.

Can anyone point me to a circuit diagram of an HF amplifier that uses a
PNP transistor instead of NPN?

I know that they behave the opposite, but unfortunately I haven't been
designing BJT amplifiers in the past years and I'm now a bit lost.

I have some spare PNP power transistors with a decent GBW (or ft), and
I'd like to see what happens if I use them as the PA stage of my
homebrew CW transmitters.

Thanks,
Paolo IK1ZYW