> From: Rich Measures <measures@vc.net>
I wrote:
> >If you look at N7WS's data, and his conclusions, the stock AL-80B
> >suppressor is essentially equal to the nichrome model near
> >the frequency where stability is a problem, although the stock
> >suppressor does lower SYSTEM Q at VHF slightly more than the
> >nichrome replacement.
Rich replied:
> Good advice, Mr. Rauch. I looked. How could Wes have been measuring
> 'SYSTEM Q'?
System Q can be calculated from the parallel impedance value of the
suppressor components, and the knowledge of the rest of the system's
impedance.
Even without knowing the exact value of the rest of the system's
impedance, one thing is certain. A higher value of parallel
resistance in the suppressor system decreases system Q, since the
suppressor is placed in SERIES with the anode path.
> It seems that Mr. Rauch admittedly missed the boat on admittance (Y). A
> direct short sends Rp up through the roof.
What definition of Rp are you using Rich?
Are you really claiming if I parallel a zero resistance wire with a
50 ohm resistor, the parallel resistance of the two components is
infinite?
Wes was measuring two components in parallel. Look at the impedance
of the nichrome by itself (8333 ohms) at 200 MHz, and the tinned
copper wire by itself (43478 ohms). When that impedance is placed in
PARALLEL with the fixed resistors (both approximately 100 ohms), the
result is the terminal to terminal impedance of the suppressor as
viewed from the outside world. It is THAT impedance that is
considered to be in series with the anode system.
The higher the value of that resistance (since it is in SERIES with
the anode impedance), the LOWER the system Q.
In both cases, it is VERY close to the same result. The suppressors
are essentially the same at VHF, but the nichrome has much lower Q at
HF.
By the way Carl, you may not be familiar with network analyzers.
Components don't get "hot" and change value on a network analyzer.
The 109 ohms was the value of the resistor that happened to be used,
because of resistance tolerances in the components. What Wes was
saying was the actual value was 109 ohms, normal tolerance for a +
- 10% 100 ohm part.
Peter, you are correct about using a "different suppressor for
different applications or tubes". Tubes like the 572B and 811A
require larger suppressor inductance and higher resistance values
than other transmitting tubes because the tube's internal leads are
so long.
73, Tom W8JI
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