It's not too easy to design a pi output network that has a Q of 12
from 160 through 10 meters. Usually for a RF amplifier that is band
switched, output (efficiency) suffers, usually at the ends of the
frequency coverage range. The thing that usually gets a ham amplifier
on 160 is that the fixed value output loading caps can't handle the
current and change value. If cathode driven, then the filament choke
may not be big enough on 160 also.
I am not aware of a low cost source of production quantity edge wound
coil stock, of the type made by EF Johnson using mycalex, and coil
clips and other hardware if purchased new, are pretty expensive also.
You can't reasonably make a recommendation for construction based on
flea market purchases, when a manufacturer's designer has to think of
a design in terms of production parts availability and purchases in
amounts of 1000 of each item. There are some great parts out there
but if you want to make 1000 amplifiers you may not be able to use
them and pass the economy of scale cost on to the customer.
Hams who want high efficiency all across HF and 160 probably need to
run three amplifiers each optimized for part of the coverage, or use
plug in coils. There's nothing wrong with plug in coils and they
really help with Q. The problems are that most users want a switch on
the front panel or everything automatic, liability, running the amp or
transmitter with an access panel etc.
73
Rob
K5UJ
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