Tom, W8JI, commented on the suggestion in the QST article (which I haven't seen
yet) of using small 470k resistors across the diodes. I seem to remember
having this discussion previously, and having spoken at the time to the group
in our company who made diodes (and SCRs and triacs and IGBTs in the several
thousand volt, several thousand amp range for traction purposes) their advice
was that unless all the diodes are from the same batch, you couldn't be sure
that they'd all avalanche at about the same voltage. Avalanching can be
controlled, but only to a certain extent, so if you are replacing one diode in
a stack with equalising resistors, it's worth keeping the resistors. Or better,
is to replace the whole string with new controlled avalanche diodes from the
same batch and no resistors. But if using the resistors, they should be rated
for the voltage, which small resistors are unlikely to be. If they are old
carbon resistors, throw them out - more than 10 years old, or be
en heated, they're unlikely to still be within 20% of nominal.
A final point about QST. Like all amateur magazines, it has to appeal to a
generally less technical audience than of yore. But the League is about a lot
more than just QST, and without the League's support of IARU, you wouldn't have
any need for amplifiers, because you wouldn't have any frequencies to use them
on. My gripe about the ARRL (and I am a member) is that they don't blow their
own trumpet enough about the work they do with IARU at the ITU and CITEL. Of
all the national societies, only the JARL come close to doing the amount of
work ARRL does in supporting IARU at the ITU - where it really matters! So in
many ways, foreign amateurs are better represented where it matters as ARRL
members than as members of their own national society.
73
Peter G3RZP
.
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|