The problem of suppressors becomes a deal when the VHF parasitic is enough
close to the operating frequency of the amplifier.
When the ipotetical VHF parasitic happens very off the HF range, let's say
UHF as it is with most modern ceramic triodes, any suppressor or even no
suppressors work fine.
When the suppressor has to be effective not very much off the operating
frequency one has to realize that, or the stability won't be 100% achieved,
or some power will be lost in the highest bands.
Incidentally, at the operating frequency (i.e. 10m) the lost power by wire
ohmic resistance could be exactly the same lost in a suppressor with
resistor, if the inductance is the same.
To compare a classic suppressor with one using a resistive wire it's enough
to transform the parallel resistance (shunt) to its series equivalent.
73,
Mauri I4JMY
----- Original Message -----
From: "measures" <2@vc.net>
To: "Tom Rauch" <W8JI@contesting.com>; "Jon Ogden" <na9d@mindspring.com>;
"Peter Chadwick" <Peter_Chadwick@mitel.com>
Cc: "amps" <amps@contesting.com>
Sent: Friday, March 23, 2001 5:11 PM
Subject: RE: [AMPS] SB-220 Amplifiers and Garage Sales!!
>
> >
> >Are you guys playing Rich's word games again?
> >
> >Wes, the person who made the measurements, concluded there
> >was no advantage to using nichrome. Rich, despite making an
> >agreement to not "cook" Wes' data, did exactly that.
> >
>
> >Rich re-worded things.
> >
> Rich did not change any measurement.
>
> >> Rich says:
> >>
> >> > Rp was 101-ohms for a resistance-wire suppresor vs. 166-ohms for a
> >> >copper-wire suppressor.
> >>
> >> Something puzzles me here. If the suppressor provided the whole plate
> >> load impedance at the parasitic frequency, then the gain would be
> >> reduced by only 4.3dB by lowering the parallel resistance from 160 to
> >> 101 ohms. This may be enough to just stop the parasitic, but doesn't
> >> appear to my mind to give enough margin to ensure stability.
> >
> >A lot of things should puzzle you Peter:
> >
> >1.) The frequency Rich selected is LOWER than the frequency
> >where the amplifier actually would oscillate.
>
> Wes choose 100MHz. This is close to where parasites typically occur.
>
> >This makes the
> >difference larger than it really is, since Rich's suppressors lower
> >the Q most at low frequencies.
> >
> >2.) The suppressor Wes tested was NOT the hairpin Rich
> >recommends, it was a larger inductor made exactly the same as
> >the stock suppressor except with nichrome. If you actually use
> >Rich's hairpin, VHF Q actually INCREASES over the stock
> >suppressor when the whole system is considered.
> >
> 100nH with a coil-inductor is the same as 100nH with a U-inductor.
>
> >> But in reality, the suppressor is only part of the plate load
> >> impedance. As a result, the change (percentage reduction) in the load
> >> that the plate sees is even smaller, so the gain margin between
> >> oscillation and stable operation becomes even less.
> >
> >Bingo. You won't find that on Rich's web page.
> >
> >The entire thing is nonsense. I measured the VHF anode Q of a
> >amplifier with a pair of 3CX800's with a stock suppressor, and again
> >with Rich's nichrome. The VHF Q increased when the Measure's
> >suppressor was used.
>
> . Resistance wire produces a higher Q than copper or silver?
> >
> >That's because Rich's suppressor has less Rp, and when that Rp
> >is placed in series
>
> the "p" in Rp stands for parallel.
>
> > ...with anode lead the reactance of the anode lead
> >dominates the system.
> >
> jabberwocky
>
> >Rich focuses on Rp because he can make a pathological argument
> >that "less Rp is better".
> >
> is less VHF gain is better?
>
> >Of course anyone who understands the system also knows the
> >exact opposite is true. When a lower Rp is inserted in series with a
> >fixed reactance, system Q increases.
> >
> welcome to the Rauchian world.
> >........
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
>
>
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