> It appears that the suppressors that Wes tested are not the same
> suppressors that Rich provides today. Rich advises that the length of
> wire in today's supressors is the same as the length of wire used in the
> unit Wes tested. But the one Wes tested was wound about a resistor,
> whereas "today's" suppressors apparently are hairpins.
Wes' goal was to prove if nichrome made the suppressor better at
VHF. He measurements show it does not, but then that's what
anyone who understands parallel R/L circuits would already know.
If you look at the page where Wes graphs the results, the bottom
sentence concludes that a simple slight re-adjustment in resistor
value would make the two suppressors be IDENTICAL at VHF.
The only difference is nichrome had a lower HF Q.
Rich's hairpin, as you pointed out, is not the suppressor tested.
The hairpin would have less inductance, and thus higher system Q,
when installed in the anode system than a conventional suppressor.
I sit around chuckling at the people who increase VHF Q, and
think it somehow increases VHF stability.
Nichrome suppressors do have an advantage in PA's that have
tubes that oscillate at HF or just above HF. That is the reason they
used nichrome in the 20's.
In the pre-WWII era, many tubes were unstable at 10-50 Mhz...very
near the operating frequency. With poor layouts, thin long leads
and coarse grids in the tubes, and floating plate tuning capacitors
in link coupled tanks...HF and lower VHF stability was a severe
problem. The systems needed de-Q'ed at HF and lower VHF.
If you are using 100TH's or even 250TH's, a wooden or bakelite
chassis, and a tuning cap floated from ground through bypass
capacitors and a RF choke, nichrome suppressors are absolutely
necessary.
Nichrome or other distributed loss systems can be very helpful
when the PA oscillates near the operating frequency, and you have
some gain and power to waste.
73, Tom W8JI
w8ji@contesting.com
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