Hello Phil,
This is my first time to write to you directly but I read this e-mail
with some interest and after a night of thinking about it I had too many
questions to ask.
Lets start with something that made me ask HUH?
> > People really get far too carried away with Q, because efficiency
> > changes very little with Q as long as tank losses are low. Factually
> > the lower the loaded or operating Q becomes, the higher the
> > efficiency becomes until Q is the square root of the impedance
> > ratios plus a tiny bit. When loaded Q drops below that value,
> > network phase shift is 90 degrees or less and the network no
> > longer behaves like a Pi Network.
OK so far. Not being an engineer I have to accept it as fact and I have
no problem there.
> This is easily observed when one has the luxury of a roller inductor
> in the tank circuit. If you are looking for a big peak when the Q is set
> to 12, you are in for a disappointment. Makes more sense to tune for
> "max. clean" on the 'scope.
OK now I am a bit confused. What does max clean on the scope mean in
this case? Are we talking about a spectrum analyzer? What?
In the past few amps that I built, (pair of 813's in GG/ 6 sweep tubes
in GG/ 10ea. 1625's in parallel GG) all I did was use a small pi matching
network or some type of input tuning system (tube exciter days) and move the
tap on the output tank around a bit while tuning up into a dummy load in the
middle of the band while noticing the output power with drive and the
position of the tune C. More tune C meant a higher Q as it also coincided
with less L. The position of the tap was moved back and forth across a
range until the power output dropped off on either end of the coil tap
setting with the same input power and drive. The center position of the two
extremes was where things got hard wired and we went on our merry way. I
have no idea what the Q was but I did see a place where things did sort of
peak, or perhaps I should say where they didn't fall off. If I read you
correctly, you say that isn't the case. If that is so, then how do you tune
up an amp with a roller inductor? What am I missing here? Enlighten me,
please?
Mike Baker K7DD
k7dd@earthlink.net
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