>>> I'd like to improve performance on 80 & 160M
>>> QRO and read of one Ham changing the C1 240pf
>>> input series cap to 750pf and C2 114pf to 675pf.
>> Why not add some 250 or 500pF doorknob caps that can be switched in
>> in parallel with the current capacitors?
> Hey! I was going to suggest that.
> Actually it's a good way to increase the range without giving up the
> resolution of the smaller tuning cap.
> There are a number of amps that take that approach with their final tuning
> one being the old HT33 series by hallicrafters that uses a simple knife
> switch tied into the band switch to add capacitance on 80.
>> The actual switches will take some care, but maybe some vacuum relays
>> could be used for an elegant solution, or knife switches with pull
>> cords or push rods through the outside of the case for a cheap
> Take a look at how the old hallicrafters switches work in those HT33s.
> are not much more than a plated copper arm that pivots on a screw through
> piece of plexiglass
As an added note, the Henry HF amps use a series of plastic cams on a shaft
geared to the band switch.
There is a 2KD classic on e-bay that has several photos that show the cams.
Today is 18th and it should be there of a bit over 5 days. Watch for line
wrap on the link.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> There's also a cam on a shaft tied to a knob, or push-pull switch, disk of
> plesiglass with arm mounted on one side. In the case of the old B&W tank
> coils/band switch we tied the caps to the 80 meter position. Let your
> imigination be your guide.
> and good luck,
> Roger Halstead (K8RI and ARRL 40 year Life Member)
> N833R - World's oldest Debonair CD-2
> www.rogerhalstead.com (Use return address from home page)
>> You are certain to give away some high-end tuning capability because
>> the minimum capacitance of a big air variable will probably still
>> present a fairly low reactance on upper HF.
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