Tom,
I haven't really analyzed this problem carefully, but I always find it
helpful to use extremes (as you have) to bracket the problem.
As you point out, if Rp is lowered to zero, then the Xp is shunted
completely and the suppressor does nothing. The other extreme,
very high Rp also leads to the same result as it suggests a
inductor with inductive reactance Xp in parallel with an infinite Rp
which is also a high Q case (in this case the VHF resonance will
be shifted due to the reactance Xp). So I am wondering if you don't
have to consider the ratio of Xp to Rp in order to determine the
efficacy of a suppressor. In other words, for a fixed Xp (equivalent
parallel inductive reactance of the suppressor), if I sweep Rp
from zero to infinite resistance, at what point do I achieve mininum
VHF tank Q? I would argue that both zero Rp and infinite Rp are
both high Q cases, so lowest Q lies somewhere in the middle.
So does it make sense to generalize one way or another without
also considering Xp?
73 de Mike, W4EF...................................................
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: " AMPS" <amps@contesting.com>
Sent: Sunday, March 09, 2003 4:51 PM
Subject: Re: [Amps] AL-80B questions
> > >In that case, lower series resistance means higher Q in the
> > >system.
> >
> > ** True, but high series resistance produces low parallel-equivalent
> > resistance, which lowers amplification. [Ref. figures 12 and 18 on my
> > Web site]
>
> Sorry Rich, that is not true. I don't expect you will answer this point by
> point, but it would be interesting if you could refrain from insults and
> smoke screens and try responding point by point.
>
> First, there are a few meanings of Rp that can confuse people, so I'll
say
> what is what when I use Rp to avoid confusing anyone.
>
> You claim lower Rp means less VHF gain. Lower Rp (plate load resistance)
> does NOT mean less VHF gain, because of shunting reactances.
>
> I can give a very clear example of this, that will help people who want to
> understand the system picture it better. Consider an audio amplifier with
> very high Rp (plate load resistance). It is well known that such
amplifiers
> roll off at high audio frequencies. The cure to high frequency rolloff,
> outside of adding intentional gain compensating feedback, is to reduce Rp
> (plate load resistance). This is because the shunting reactances of wiring
> and the tubes actually roll off an amplifier's gain. This has always been
a
> big problem with broadband amps with tubes, especially big tubes. This is
> why tube-type television sets had to use peaking coils in video
amplifiers,
> and why virtually no one could build a broadband tube amplifier with high
> gain and high power in a single stage!
>
> What we really want in a PA is to prevent low-loss resonances at VHF, or
to
> simply move those resonances to a different spot than where the control
grid
> is resonant.
>
> This is where the problem with your hairpin suppressors, or small one or
two
> turn suppressors, comes in. Those suppressors have a very low Rp (parallel
> equivalent resistance). This parallel equivalent resistance is what the
> parallel combination of R and L "look like". It is in SERIES with the
> impedance of the rest of the anode system. When that Rp (parallel equiv
> resistance) is low, it allows the leads in external connections to have HI
> Q.
>
> Let me give a clear example of where you talk in a circle, this is pretty
> easy to follow.
>
> The AL1500 has a specific brass material used in the anode lead, for the
> entire length of that lead. If I measure Rp (parallel resistance of that
> lead, it is very low.
>
> You claim your suppressors are better because they have low Rp (low
parallel
> resistance), and the anode lead system in the AL1500 has even less Rp
> (parallel resistance)....yet you are especially critical of it. Why is
that?
> Why is GOOD when your suppressor has less Rp and especially bad when
another
> system has the same? The lowest Rp suppressor would be a dead short, or no
> suppressor at all.
>
> To anyone who wonders, different systems require different cures. If the
> entire anode system can have low Q (such as being from brass) and moved to
a
> different frequency than the grid and if the self-neutralizing frequency
is
> made high enough, a PA can be made unconditionally stable without any
> "suppressor".
>
> The problem I have is you claim you are "lowering Q" in long skinny anode
> leads by REDUCING the added parallel equivalent resistance placed in
series
> with the anode lead, which means you have reduced losses. The fact is, in
> most cases your suppressors do the exact opposite of what you claim. They
> reduce HF Q, while increasing VHF Q over stock systems.
>
> This is why you got into such a nasty name-calling fight with N7WS and
> others on an open forum, because they pointed this all out.
>
> That still does not mean your suppressors will ruin amplifiers, because
most
> amps...once the real problems are fixed....behave very well. In some
cases,
> like in an amplifier unstable at HF, your suppressors could actually help
> because they add HF loss. But there are a hundred ways to solve the
problems
> without adding excessive loss or lowering tank system operating Q.
>
> 73 Tom
>
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