> Hello Steve
> what i have is 500pf@10kv ,1000pf@10kv, the roller inductor is 103uh rated
> 10kv.
>
[Steve Katz] Holy mackeral! You can fit all that in a chassis?
103 uH?? At what current?? (The voltage rating isn't important, unless the
turns are spaced so closely they arc to each other, which is doubtful.)
Most roller inductors used in amateur amps are about 28uH.
> I have 4 doorknobs 1000pf@12kv and some 500pf
> The band switch is a switch craft model 88 13kv rated.
> This is my first amp of this sort so i am still not sure about some
> things.
> I have built 813s 811s and 572b amps but nothing like this the GU-84B
>
[Steve Katz] What makes the GU-84B any different from some 572B's
in parallel? Same requirements, other than I guess people using GU-84Bs are
often doing it without sockets. Plate load impedance is Ep/Ip, regardless
of the tube(s)....
> So i can use the bandswitch to switch the doorknobs in and out.
>
[Steve Katz] Normally, one would do this with 572B's, also.
Problem with a 1000pF vacuum variable is that, usually, it requires an awful
lot of shaft rotations (turns) to go from min to max; compared with an
air-variable that does it in 180 degrees. So, unless you have interesting
circuit alternatives, going from, say, the high end of 10 meters to the low
end of 80 meters could be a lot of work (crank, crank, crank).
> I am still trying to get a mental picture. I feel pretty stupid right now
> :)
> Can you explain a little bit more in detail how i would hook it up to use
> all 4 compnets?
>
[Steve Katz] Assume you're building a pi-net? I figure all the
component parameters needed for reasonable Q at full power (reasonable might
be in the 4~6 range) and determine how much padding C I might want to switch
in for plate tuning, or loading, or both; normally this is only desirable on
the lower bands like 80 and 160m, but even on 40m it can be advantageous to
switch in some padding rather than having to crank a vacuum cap through 20
rotations. Then, wire up the bandswitch to switch in those padders as
required. Obviously, in a pi-net one end of any capacitor is always at
ground potential, so you only need to switch in "one end" of any cap you're
adding. -WB2WIK/6
> Thanks for taking time to help out
> 73
> Chris NI4L
>
> Steve Katz wrote:
>
>
>
>
> Hello All
> I have a question that maybe someone can help me out with.
> I am in the process of building a GU84B amp.
> I have a 2 vac var caps and a roller inductor, I have a
> bandswitch also
> but is there really a need to use the bandswitch when you
> use vac caps
> and a roller inductor. Pro/Cons?
>
>
> [Steve Katz] Normally a bandswitch is used at a minimum to
> switch
> input tuned circuits per band. Additionally, unless you have an
> awfully
> large "load" vacuum variable, a bandswitch is useful to switch in
> loading
> padder capacitors for the lower bands like 80 and 160 meters...a
> typical
> vacuum cap can't offer the kind of maximum capacitance normally
> required to
> load into 50 Ohms on those bands. -WB2WIK/6
>
>
>
> I am still a babe in the woods on this so any help would be
> greatly
> appreciated.
> Chris
>
>
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