6V6 was the quintessential beam power audio output tube of the 1940s through
the 1960s. You can generally "read" the missing numbers if there is
anything left of the imprint by gently rubbing the tube on your hair. THe
oil from your hair will stick to what is left of the printing and make it
readable for a short time. You might take a permanent marker if and when
you finally read the number and mark the tube.


As has been alluded to in several posts, you are not limited to the exact
tube that the original project had in it. For example, the 6U8 was the
VHF/UHF RF oscillator/mixer of choice in thousands of designs. However, a
6J6 oscillator with a 6BE6 mixer will work every bit as good if you aren't
fussy about VHF reception. There are dozens of tricks you can play with mix
& match tube lineups, some better than others.

Jim


You're right, the voltages range anywhere from 3 to 33 volts. Two of
them are 6V6 tubes, so I have some hope there. Most of them are
miniatures, and some of them have the numbers missing, which makes
things really interesting.