[AMPS] Design of Plate RF Choke

[Lamb]

Question -

Assuming we can control all of the parameters of the plate rf choke (I
realize that is not possible), what are the ideal characteristics?

Primary goals are sufficient impedance throughout the range of the amplifier
and no unwanted resonances.  But, can we ask for more?  The impedance
decreases below the design frequency - which would reduce gain below the
design frequency.  That is good and easy to attain.    The next question is
how do we want the rf choke to look above the design frequency?  If it has
low impedance, that would reduce vhf gain and therefore reduce parasitics.
This characteristic ought to be desirable - but perhaps not attainable.
Perhaps the design of a rf choke that has no resonances and sufficient
impedance throughout the design frequency is all one can hope for.  Perhaps
the inefficiency and stray inductance of the plate bypass capacitor would
render the low vhf-uhf impedance of no real value.

Suppose the rf choke is replaced with a parallel tuned circuit?  Even though
this circuit, in theory. is resonant at one point, we recall that parasitics
were common even when parallel tuned circuits were used rather than
pi-network developed by Collins in the 1930's.  Buddy Alvarez constructed a
4CX1000 amplifier using a home built rf choke wound with Manganin wire (a
resistance wire).  It had no resonance.  He used no parasitic suppressor in
the plate circuit and it ran with no problem.

Another question is:

Has anyone tried to "short out" parasitics rather than "arrest" them.  By
installing a band-pass type filter for all frequencies above the normal
operating range between plate and ground, any undesired oscillations would
be dampened without the loss of a parasitic suppressor.

Comments would be appreciated.

Colin  K7FM


--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm