> >You claim lower Rp means less VHF gain. Lower Rp (plate load resistance)
> >does NOT mean less VHF gain, because of shunting reactances.
> >
> ** what shunting reactances? How can reactance effect R ?
Anyone who has tuned a tuning control on a transmitter understands reactance
can affect gain.
>
> The brass strip is in parallel with the anode?
We took everything to a parallel mode, which is the parallel equivalent
impedance of a two-terminal device.
Any system like this can be expressed in a series-equivalent impedance or a
parallel-equvalent impedance.
When we comnpare two systems, we must look at them the same way and use the
same terms to avoid confusion.
> ** Wes' table shows that the W8JI suppressor had c. 60% more Rp than the
> other guy's suppressor.
That's great news, because when the higher resistance suppressor is placed
in series with the anode lead it has more de-Qing effect.
The lowest Rp suppressor would be a dead short, and the Measures nichrome
suppressor is closest to a dead short.
The irony of this is the nichrome suppressor Wes tested actually would have
MORE Rp than the stock suppressors you sell!
> >The lowest Rp suppressor would be a dead short, or no
> >suppressor at all.
>
> ** Downtown Backwardsville. A virtual dead short in series with the
> anode would have a high parallel-equivalent resistance. A high series R
> means a low parallel-equivalent resistance, or Rp. This subject is
> covered in AC circuit analysis.
You are mixing the models.
The two-terminal device consisting of a resistor and inductor by itself had
a low Rp. We are NOT placing the low Rp of the suppressor directly from the
anode to ground, it is in SERIES with the long anode lead! It is the long
anode lead impedance it must modify.
> >
> ** so what caused the gold to evaporate off of the 8877 grid in Fig. 24
> on my Web site ? Can you name another 8877 HF amp designer who does not
> use a vhf parasitic suppressor?
Gold migration is a common problem. It is explained on my web page in the
vacuum tube failures section.
It does NOT prove an oscillation. It is actually caused either by excessive
grid current or by manufacturing defects in the tube.
> ** I do not recommend putting low-Q suppressors in series with the
> tank-L.
Your suppressors, like most suppressors, are in series between the tube
capacitance and tank input. Like it or not, that places them in series with
the tank and de-Q's the system. This is especially noticable on 15 and ten
meters, when the anode capacitance is a large portion of tank input
capacitance.
73 Tom
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