[Amps] solid-state amp "suckout"

[Steve Thompson]

Scott Townley wrote:
> I have a broadband, solid-state amp that seems to have a large-signal "suckout".  The small-signal gain across the HF band is as expected, 10.5dB decreasing to 9.5dB at 30MHz.  But under full drive, the output at 17m is down more than 3dB, and at 15m down about 2dB.  Input VSWR is <1.5:1 for all bands, small and large signal.  This is just the amplifier modules; no bandpass filtering is in place.
> Any ideas or suggestions?  
What are the modules?

Resonances in the transformers or feedback networks can cause this, but 
be prepared for your amplifiers to have unique problems. It might be 
that the fundamental frequency load line has strayed. You haven't added 
any output filtering, but the output transformer and any frequency 
'tweaking' components can cause the same effects once the harmonics get 
outside the frequency range of the transformer and start getting reflected.

It's dead easy to throw you these comments. It's a serious pain trying 
to fix the problem, even with the benefit of lots of test gear.

Steve