OK, some great and very helpful answers here. I am under manic presure from work, I will post in detail with some scope shots and a full run down of why I need it and what i want it to do, but VERY briefly I think it has more gain than I expected and / or was led to believe. I was seeing wedge shaped waveforms, almost square, out, when fed with 0 dBm sine waves from my 9good quality) sig gen. i was expecting a higher amplitude sine wave. Dropping the input level to about -19dBm results in sine waves, so i guess it's "clipping" very badly? Now whilst the exciter (my Kenwood TS-590 Drive output, meant for either amplifying for 136kHz and for feeding a transverter for other amateur bands higher than it's 6 metre maximum, is supposed to be 0 dBm, I can, by adjusting the modulation level via the PC sound card, which is how it's fed in digital modes, to a lower level, get sine waves out. So basically I am not sure how Kenwood rate this "0 dBm exciter output level". It may be i can adjust audio modulation to suit the gain of the amp. the other thing i don't undertstand is why a symmetrical square wave, when the amp feeds the x2 frequency converter it has to drive, and which is designed to go from sine to square output, shows the square waveform go to rectangular with longer top and bottoms, if you see what I mean, as the gain is changed via the amps input level. Only over a narrow input signal level do i get true square waves out.
I attach below the circuit this amp feeds, to double the 136kHz tpo 272kHz, and convert to square wave. This is required as the Class D main amp drives power FETS, and the driver chip needs double the frequency as it itself halves it.....
Thanks for all the help!