Hi Group,
I got a wild hair, and made a setup to compare a set of used Genalex
KT77's to a new MP (matched pair) of Sovetek EL34's. I was following a note
in the KT77 data sheet that stated when a KT77 is considered bad (< 9.3
ma/volt transconductance when EP, Eg2 = 250 volts held constant, and IP =
100 ma). Following this criteria, I made a test setup. I am not too sure of
my technique as it is a work in progress. I am curious that the Gm can vary
considerably when changing Vg1 +/- 1 volt from the value used to obtain 100
ma plate current. Maybe this is all wrong, but I averaged the two numbers
assuming that is the final answer. Since Genalex stated to run the screen
and plate at 250 volts, I connected them together (Fluke 8012a looks at
plate current only), so this test is in triode mode (or is it not?). For a
high voltage supply I used my Sherwood S8000 stereo amp / FM with a variac
(get ~ 250 vdc at 65 volts AC input). Hey it was there (awaiting a re-cap
job), convenient, and able to do the job!
Is the data I've taken valid? If not, can someone enlighten me? Maybe I
need to vary Vg1 less than +/- 1 volt, for better data?
Regards,
Jim Candela
Test results:
http://pages.prodigy.net/jcandela/KT77/genalex_kt77.htm
KT77 Data Sheet:
http://pages.prodigy.net/jcandela/KT77/kt77.pdf
Test Setup:
http://pages.prodigy.net/jcandela/KT77/PA110015.JPG
