[AMPS] Clipperton L parasitic choke circuit

Rich Measures measures@vc.net
Mon, 13 Oct 97 02:10:40 -0800

>Hi there Carl.....in a AMPS reflector posting that you made to
>Rich Measures on October 10 concerning B+ glitch resisors you
>briefly mentioned the Clipperton L problem that I have been
>experiencing....mainly that the parasitic choke resistors start
>to smoke when I tune up on 10 meters. The circuit consists of
>a 100 ohm 2 watt carbon resistor with a coil formed around the resistor
>(or in parallel with it) consisting of 5 turns of wire. There is
>one of these on each of the four 572B tubes. I have tried reducing
>the number of turns on the coil to 4, but the resistors still 
>smoke on 10 meters but at a higher power output level than before.
>I am thinking about using a 68 ohm 2 watt carbon resistor and
>reduce the turns on the coil to 3 turns.
>I wonder if you have had any experience with this problem with
>the Clipperton L and if so what you did to fix it.
>I am sending a CC of this to the AMPS reflector to see if
>anybody else out there has figured this one out.
>Thank you for your help es 73 de Mike/W6RW
Designing a VHF suppressor is a bag of compromises.  
-  Adding turns to Ls reduces 10m dissipation in Rs and increases VHF-Rp, 
which increases VHF voltage amplification (Ae).  
-  A suppressor that does not exhibit signs of heating at 28MHz is not 
going to have much of an effect at VHF.  
-  Reducing Rs from 100 ohms to 68 ohms is going to increase VHF-Rp and 
increase VHF-Ae (which decreases VHF stability) -- unless one increases 
-  A better Rs is the Matsushita 3w MOF type.  These resistors will 
dissipate 12w each in free air for 1 hour with no substantive problem.  
We use 100 ohm, 3w units in our suppressor retrofit kits.  The intrinsic 
L is around 11nH according to measurements by Wes, N7WS.  
-  With MOF resistors,  winding Ls on top of the Rs resistor normally 
results in arcing between the coil and the resistive film.  Side by side, 
 with a coupl;e of mm air gap works okay. 

R. L. Measures, 805-386-3734, AG6K   

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