Tremolo design options

1. Several different power-amp bias modulators: http://www.lynx.bc.ca/~jc/tremoloCircuits.html
2. Input stage bias modulator: http://www.lynx.bc.ca/~jc/supro_s6616.pdf This one is interesting because the LFO drives a source follower connected to the cathode of the input tube! Have to look at that carefully.
3. Typical Fender LDR tremolo. extensive analysis: http://terrydownsmusic.com/technotes/vibratocircuits/tremolo_circuits.htm