Good info Ian.
I was looking around trying to learn more about the various bias circuits in
use.
maybe people can provide historical views on some things I was curious about:
-This 1971 Eimac paper on a 8877 triode for 144Mhz, had a 1N3311 50 W 12V zener
for the bias.
Makes me wonder why R. Sutherland decided on 50W for that diode.
http://www.landfall.net/Radio/8877-1.htm
-The junction to case C/W is much better for the zeners in the larger DO-5
stud package..just 2 C/W max (1.5 C/W typical)
compared to 10 C/W (typical) for the DO-4 stud package. I wonder if that's
what's interesting...not that it can
tolerate 50W but that it has lower junction temps to start with, for a given DC
dissipation..because of the
better/larger package. Note that it doesn't matter how good your heatsink is,
if the junction to case thermal resistance
is the problem.
-The ability to tolerate power spikes depends on junction temperature rise in
the zener, right?. So starting from a low
junction temp adds margin?
-rfparts.com has the reverse polarity 1N3306B (50W 7.5V) for a reasonable
price, and claims to have the mounting hw. So
I ordered a pair. It seems easier to drill larger 1/4" holes and use the stud
diodes, then use say the flatter TO-3
packages and say TO-3 heatsinks or something like that. So I ordered a pair of
those to try.
It appears that some amps do use the TO-3 packages though?
-The 1971 Eimac paper mentioned using a smaller zener with a 2N3055 transistor
on a heatsink, instead of the 50W zener.
I thought that was funny, because some web sites I've read mention something
similar, like it's a new idea.
Also saw people mentioning using zener plus mosfet, at least for audio amps...
I guess you could size a pretty large power transistor? How come we don't see
more of these simple lower power
zener+transistor circuits? or do people do this?
Ah, I'm reading Ian's Triode Board manual. I guess that's an example of taking
that to more extremes.
-kevin
AD6Z
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