Dave, the 2SC5551 is a bit faster than 300MHz!? A spectrum
analyser is a very useful tool but not necessary to detect
spurious oscillation. Measure the current consumption on an old
analogue multimeter and run a portable broadcast VHF receiver on a
distant weak signal. Touching different parts of an oscillating
amplifier will generally cause a change in current draw and an
audible difference to the broadcast signal.
Another useful trick is to use a simple diode demodulating probe
and audio amplifier to listen to the amplifier output, touching an
oscillating circuit will? be clearly heard. Making fault
conditions something you can hear is very useful as you can then
devote your eyes to what you are touching.
I would agree with the point about high Ft devices, unless you
have a lot of experience in UHF/Microwave thinking there are sound
reasons in using older slower devices. A 1dB difference is
insignificant to most users. The reality is that most users are in
Urban locations with high noise levels slight differences in noise
performance will not be noticeable.
73, Alan G8LCO
