To: <amps@contesting.com>
>> Date: Tue, 19 May 1998 10:04:39 -0500
>> From: Jon Ogden <jono@webspun.com>
>
>Hi Jon,
>
>> >Can you explain how lower Rp in the suppressor produces less VHF gain?
>> >If lower Rp means LESS gain, why use a suppressor Jon? What is the Rp
>> >of a dead short?
>>
>> Arrgh! I thought we worked through all that math! Gain is directly
>> proportional to Rp.
>
>I assume you are talking about voltage gain, and not power gain.
They are inexorably related.
>When the tube is delivering power and consuming power from the driver,
However, in a Class AB1 amplifier, the tube consumes virtually no power
from the driver since it draws virtually no current from the driver.
>more plate load resistance can mean either more or less
>power gain.
ok. However if load resistance is low, voltage amplification is low.
>
>> Rp is different from the R of the supressor
>> resistor. Did you not just read Ian's notes?
>
>No, I deleted most of the messages that built up over three days.
>Ian almost never needs checked. By the way, it would be better if we
>avoided jargon like Rp. Rp means different things in different
>applications, and use of excessive jargon can confuse everyone.
In Wes' measurements, Rp means only one thing.
>
> >Anyhow, if gain is proportional to Rp doesn't it makes sense you
>>want to lower it?
>
>If you want to decrease voltage gain, that is true. The problem
>with that statement, perhaps Ian addressed this point, is suppressor
>"Rp" or impedance is one part of system impedance "Rp" seen by the
>anode.
agreed, however, the suppressor remains the principal means of reducing
VHF voltage amplification.
>The suppressor has little effect on the SYSTEM unless the
>impedance of the suppressor approaches or exceeds the impedance
>presented to the tube while "looking into" the tank.
There are two loads presented to the anode: the HF load, and the (VHF)
load at the anode-circuit's VHF self resonance. The HF load is presented
by the tank, and the VHF load is presented by the VHF suppressor, the
anode leads, and by whatever R and X perchance exists in the Tune-C. .
The tube has a HF gain. The tube also has a VHF gain, which is mostly
determined by Mu and by load R, of which VHF-Rp is undoubtedly a part. I
do not see a relationship between the VHF load R and HF load R, as Mr.
Rauch seemingly asserts.
>
>That is why a direct short, with a parallel equivalent resistance of
>zero ohms, will not improve stability in an unstable PA. Lower
>suppressor impedance is not always better, as a matter of fact it is
>almost always worse!
I believe lower suppressor Z is always better for building VHF
oscillators. Curiously, the Ameritron AL-1500 has a zero-ohm VHF
suppressor because it has no suppressor whatsoever.
>It's easy to see a suppressor's impedance
>MUST be a large fraction or more of the impedance of the system it is
>installed in, or it does nothing at all.
>
RRR
>Now imagine all the many layouts using different tubes that all
>require about the same suppressor method and values. Does it
>sound likely that one idea is the ONLY sure-fire cure, works in
>every case, is better than any other metod, and the cure would always
>be a suppressor of "R? + jX?" ohms impedance?
>
Did I say that that there was a sure cure, or that all suppressor's
should always have the same Ls and Rs. . . This whole argument is
laughable. OK, we want to design and build a VHF-lossy device. More R
means more loss. Does it make more sense to make the device out of
silver-strap or to make it out of wire which has 60 or so times more R?
.
>Another thing to consider, and to keep in mind, is the suppressor
>tested was not even the design marketed! The unit tested was of
>totally different construction, with more inductance.
The resistance-wire suppressor that Wes built and measured had
75uH@100MHz. The (W8JI/Tom Rauch) copper-wire suppressor had
101uH@100MHz.
>My puzzlement
>is how anyone can sell something claiming it is a cure or improvement
>with having any data about any impedances, either in the equipment or
>in the replacement part.
Have Wes' measurements been cancelled?
>
>> You cricizie the "hairpins." What difference does it make what kind of
>> inductor one uses? It still has inductance?
>
>The hairpin has less inductance than the suppressor tested.
The inductance of a hairpin/one-turn inductor depends primarily on the
length of the conductor. In an 8877 suppressor, if more than roughly
40uH is used, there can be serious consequences for Rs 28MHz. However,
in a 3-500Z suppressor, roughly 100uH works ok, except for 28MHz
RTTY-broadcasting with a 4000v anode supply.
>IMO, if one is claiming results and misusing the data, he should at least use
>a component similar to the one being marketed.
>
>> Please explain why lower Rp is not always good.
>
>Rp where? What Rp? Plate load impedance or suppressor impedance or
>tank impedance or what? What Rp do you mean?
>
In the world of magic, this is called misdirection.
>This is like calling a pi-net input cap C1. C1 can be any capacitor.
>In many amps, it winds up being a bypass cap on the power line.
>
say what?
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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