Eddy asked,
"Good Morning All,
Am I missing something here...?
Extensive research here into years & years of ARRL HANDBOOKS, Bill Orr
HANDBOOKS, and the internet have shed precious little light in the matter of
optimum / minimum values of inductance for plate chokes in the B+ leads of
our tube-type linear amplifiers.
Have a look-see yourself: in designs that feature amplifiers that only go as
low as 3.5-MHz, you'll see chokes that range in value anywhere & everywhere
from 200-uh, to 50-uh. On 160-meters, I've seen quoted values as high as
1.0-mh., and others as low as 200-uh.
Just what, exactly, is a "...minimum reactance" for a choke, on a given
frequency band, to do its job effectively, anyway...?
I know confusion can creep in in the form of the self-destruction of these
parts if the hapless home brewer happens upon a band where there's
self-resonance in the choke...but that issue aside, is this all some matter
of "...by gosh & by golly black magic", or are there very real minimum
standards & parameters that we should adhere to...? And if so, where are
said standards published...?
I certainly can't find them via "...the usual" routes --- but again, I must
be missing something here..."
~73~ Eddy VE3CUI
Eddy,
Minimum value is mainly the concern on 160M. A simple test can be performed
with a dip meter coupled into the tank coil, while connecting and
disconnecting your plate choke. A choke of ample inductance will hardly
change the resonant frequency of the tank circuit at all. A too small value
will reflect "negative reactance" into the tank, and that will be manifested
as requiring more capacitance setting of C1 in the pi-net, a result of too
much RF current flowing in the choke's winding. The best plate chokes are
'invisible' to the tank circuit.
73, Roy, K6XK
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