Parasitic oscillations look beautiful but sound horrible. Even if you can't actually hear them (ultrasonic) they sap power and can severely damage an amplifier!!

Musicman RP 112 Sixty-five            JMI Vox AC 10
Elpico AC52                                     Carlsbro CS 60
Filmosound Amplifiers                      Hiwatt Lead 50R
Lab Series L2                                   Burns
Lab Series L5                                   Fender Twin Reverb
Selmer Constellation 20                   Fender Musicmaster Bass
Selmer Treble & Bass Mk 2              Impact 60
Schaller KV40                                   Northcourt 50
Fender 5F1 Champ                           RSC Bass Major
Traynor YGL 3 - Mark 3                     Mystery Amp
Watkins Westminster                         Denco 912-Plus
Denco 912-Plus                                 Interesting Waveforms
Wem Dominator Mk 3                        Mullard 5-10
Wem Watkins Copicat Mk 3               Decca Amp