[Amps] Cathode input circuit

[Ron Youvan]

Mike Lord wrote:

> A question for the group.  Some time back, ZL1AXB published a circuit for a
> single 813 grounded grid, using a tuned coil input circuit.  He referred to
> it as a "bifilar wound coil."   I built the amp and it works like a champ.
> /*snip*/  Pat's circuit covered 40 - 10 meters.
>   I would like to use this circuit on 80 and 160.
>   Is there a formula for winding the coil?

   Think of it as a plate tank (parallel resonant circuit) for a RF amplifier
100 Watt stage with the plate tank coil wound with very small copper tubing
with a (or two) wires threaded through it.  The resulting inductance and the
accompanying capacitance/s should be quite similar, the coil is tapped in
normal auto-transformer manor.  (used backwards)
   Shorting some turns (at the end furthest from the low impedance tap) should
change bands just like a regular tank circuit.
   Generally a 40 meter coil will have about twice the inductance of a 20 meter
coil and an 80 meter coil will have four times the inductance of a 20 meter coil.
and so fourth.
-- 
    Ron  KA4INM - nothin's quite as sure as change
                  from "look through my window" - The Mamas & The Papas