On Thu, 22 Oct 1998 19:41:08 -0400 "W/Z Kornienko" <zak@goes.com> writes:
>
>How does one minimize circulating currents in the pi-net
>of an amplifier, especially on 10M?
>
>
> 73 de Walt Kornienko - K2WK
Circulating currents are not as much a problem ( with a decent Q design)
as RF heating losses thru undersized components at 10M.
The primary problem with the Q is when the amp is designed to cover
160-10M and the Tune cap is 250pf or larger. ( I am talking about air
caps only) The typical minimum C is then 20-25pf just in the capacitor.
Add in stray C and the tube C and suddenly the 10M tank coil becomes very
small, the Q goes to hell and the smoke begins.
One way to get around this is to tap the Tune cap in the middle ot the
10M coil. This has the effect of requiring 4X the C previously so you
can now design a decent Pi-Net. BTW, the other bands thru about 20M are
affected in decreasing amounts so their L will have to be slightly
increased to compensate for the loss of half the 10M coil. This was an
"easy" way to get around the expense of vacuum variables and using large
bread slicers in a pair of 4-1000A's.
73 Carl KM1H
>
>
>
>
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>
>
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