Michael wrote:

Can someone recommend a satisfactory test unit to measure 'peak'
frequency coming from an amplifier.

Thanks

What exactly do you mean by "peak" frequency?

An amplifier typically reproduces the input signal, with a little bit of
distortion and noise added. Are you talking about the frequency response
of the amplifier, or are you looking for oscillations? For the former, a
scope and a function generator works fine. For the latter, you need a
good scope or a spectrum analyzer. In both cases, you need to have a
load that resembles speakers used (assuming you are testing power amps).