Wanted: education

[Mark Graalman WB8JKR]

  Hi Ed,

 I think its just the way things were done over the years, typically
you only need enough inductance to cause the choke not effect
the circuit it across, usually an inductive Z of about 5 times the
source Z is quite good enough. A choke of about 250-300 ohms
Z would work fine on the output 2.5 mh certainly isn't needed.
 The same 2.5 mh choke would probably cause too much voltage
drop in the cathode which would have the effect of increasing the
operating bias. You could put a 22 uh choke (483 ohms at 3.5 mhz)
on the output and it would work fine as well. Actually for protection
instead of a choke on the output you could use say a 500 ohm wirewound
resistor and it would work just as well as a DC path in the event the
plate block capacitor failed, it only has to last long enough to blow the
supply
fuse.

73,  Mark  WB8JKR


On Thu, 10 Jul 2003 21:28:14 -0700 Ed Richards <k6uuz at JUNO.COM> writes:
> Hi all;
>
> In working with RF chokes I noticed in several ARRL handbooks the
> circuits for amplifiers frequently use an inductance of 22 uh for
> the
> input choke; grid to ground for grounded cathode, or filament to
> (RF)
> ground for grounded grid amplifiers. However the same circuit uses 1
> to
> 2.5 mh choke across the antenna connector. Why such a large
> difference in
> inductance when the frequency is the same (3-30) mc? An explanation
> would
> be appreciated. Thanks.
>
> Ed Richards K6UUZ
>
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