[AMPS] Suppressors, measurements, and acrimonious blather

measures 2@vc.net
Thu, 3 Aug 2000 08:08:14 -0700

>> 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.
Are you making this stuff up, Tom?.  Anyone who reads Wes' numbers knows 
>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.
VHF Q always decreases when L-supp increases.  However, as L-supp 
increases, dissipation in  R-supp increases exponentially on 10m.      If 
R-supp burns out, trouble could ensue.  As I see it, the advantage of 
resistance-wire is that it decreases the dissipative burden on R-supp.  
Wes is right in that the VHF Q can be reduced similarly with a 
copper-wire suppressor by simply increasing L-supp.  The trick is to keep 
from destroying R-supp.  

>The only difference is nichrome had a lower HF Q.
Please read Wes' measurements to see if Tom is blowin'  smoke.  

>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.
A virtual Porcine Bubblebath.  Hairpin/U-inductors can easily have more 
inductance than a coil inductor.  
>I sit around chuckling at the people who increase VHF Q,  and 
>think it somehow increases VHF stability. 
At 100MHz, the copper-wire suppressor exhibited a Q of 2.2.  The 
resistance-wire suppressor exhibited a Q of 1.2.  
(see Wes' measurements)

>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 
>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.
In G-G service, I know of no tube that has enough feedback C to oscillate 
at HF.  The grid acts as a pretty good shield until grid resonance is 
reached.  For the 3-500Z, this frequency is around 85MHz.  
later, Tom

-  Rich..., 805.386.3734, www.vcnet.com/measures.  

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