I thought some of you might enjoy my experiments with a tube of a different color. You may have read about using Vacuum Fluorescent Display (VFD) tubes in amplifier or oscillator circuits - I've been fooling with one in a Hartley and it works surprisingly well. You can find some info here:
https://docs.google.com/?hl=en&tab=wo&authuser=0#folders/folder.0.0B98akUlPIomlYWE0YTlhZmYtYjJkNy00ODExLTgwYjMtYzM1ODMwYjZlZGVkAll VFDs seem to behave differently - and none work like we expect (just look at the transfer function curve). But as long as there's power gain it'll oscillate just dandy - drawing about 3.5 ma from a 50 volt B+ supply for 170mW input. It works fine on BC band thru 80 meters but I haven't tried to go any higher. This VFD came from an old microwave oven control board, and has all anodes and grids wired in parallel.
At this power level, I get pretty decent-sounding AM audio by using a universal output transformer in series with the B+ as a mod transformer, with the 8 ohm winding driven from the output of a CD or MP3 player. Makes a unique way to send old time radio programs around the house (or the Massacree, in four-part harmony!)
73 and HTD,
Bob W9RAN