> Phil, thanks for the following:
>
> "A roller coil gives the advantage of being able to tune the tank
> for maximum efficiency at any power setting and frees one from many
> hours of tapping a fixed coil in place in a new amp.
>
> It is very simple; you tune the tank circuit for maximum power output.
> With a roller coil, you just have one more item to tune.
>
> Antenna tuners with roller coils work the same way. A tapped coil
> may not be close enough to give a perfect match in every case."
>
> (((73)))
> Phil, K5PC
>
> BUT,
>
> Couldn't (wouldn't) maximum output likely correspond to a rather low-Q
> setting of L1, rather than the usual 10 or 12? With a high L to C ratio
> in the pi-net, efficiency is improved at the expense of harmonic
> attenuation (low, loaded tank Q).
During the testing stages of a new amp, the second harmonic is
looked at to see that it is down around 35 db for a Pi and around
50 db for a Pi-L network. The position of the roller coil is noted on
the turns-counter, and noted for future use as a starting point when
returning to that particular band of operation. On the larger low bands
(80 and 160m) several readings of harmonic suppression can be
logged accross the band. for future refrence. There is nothing magic
about a Q of 10 or 12, as you have a fairly wide berth of good
suppression of harmonics if you are in the ball park. (Q's of 6 to 16
are reasonable) IOW, you will have a turn or two of the tank coil
to peak your output before you start affecting harmonics.
> So, it seems to me, just tuning all three components for maximum, full
> bore output, could end a person up with an undesireable loaded Q tank
> situation.
Only if you start off with the components positioned far away from your
origonally logged settings.
The most efficient amp I own is a Henry 4-K Ultra. The tuned input
roller coil an capacitors, the Pi coil, the L coil and C1 are all ganged
together on one knob, so that on any frequency between 3 and 30mhz,
all the components are exactly where they need to be for very high
efficiency and high harmonic suppression. Do not attempt this at
home! It must have taken the guys @ Henry many hours to get this
design right, but you get the point.
I hope this helps, Roy....
(((73)))
Phil, K5PC
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