The way I see it the 200:50 ohm bifilar xfmr reduces the loading cap
value but doubles the voltage requirement and eliminates the need for a
choke to ground in case the plate blocking cap(s) fail. It does not
need to be a super well designed xfmr since a little leakage inductance
can be compensated by the PI network. I have one in an amp (pair of
3CX800s) of mine that is 30 bifilar turns on a T200-2 if I remember
correctly.
73,
Larry, W0QE
On 10/20/2013 11:03 AM, Bill Turner wrote:
ORIGINAL MESSAGE: (may be snipped)
On Sun, 20 Oct 2013 00:51:44 -0700, N7CXI wrote:
Assuming adequate core/wire sizing and airflow, can anyone think of a
solid reason *not* to design a legal-limit HF amp output tank for 200
ohms, then use a 4:1 "un-un" transformer to step it down to 50?
REPLY:
If the only reason to do this is to use a smaller load capacitor, I would
suggest instead to switch in some doorknob type padder caps instead. IMO, a
pi-net is a better impedance matcher than a transformer. Lower loss, less
cost, more reliable. Designing a broadband transformer is tricky business, a
pi-network is relatively easy.
73, Bill W6WRT
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