[Heath] Fw: SB 200 Parasitic chokes

[Paula Uscian]

Here's what I sent directly to John regarding parasitic chokes for the SB-200, which may be of interest to the larger group.
 
73 Paula k9ir

----- Forwarded Message -----
From: Paula Uscian <pmuscian at sbcglobal.net>
To: John King <k5pgw at yahoo.com> 
Sent: Thursday, January 10, 2013 2:23 PM
Subject: Re: [Heath] SB 200 Parasitic chokes


John, here's the info I have on building replacement parasitic chokes for the SB-200.
 The new parasitic chokes are made from 3 x 150 ohm 2 watt carbon compound resistors--6 reqd in total for 2 chokes, check eBay, You need to get as close as possible to 50 ohms and no less than 6 watts.
 
The new coils are 2 strips of copper plate (for example, copper flashing material) cut 85mm x10mm x1mm and bent around a coax connector body to form a U shaped inductor. Drill a small holein each end.
 
The resistors will all sit next to each otherin a triangle shape with the wires sticking out each end. You can windtwo of the resistor leads (on one side) around the third lead and soldered them in place and cut off the excess wire so only the third lead is its original length.
 
Solder the two leads wound around the third as close to the resistor bundle as possible. Then the bunch of resistors can be fitted in the U with the wires sticking out of the drilled holes, squeeze back together the U so that the ends are next to resistor body ends,and solder the U to the protruding wire.
 
As you noted, it takes a bit of experimenting to find the best fit for the replacement chokes--but it is possible! If you can, try to have the chokes at right angles to each other.
 
I've attached a photo of an installation done along these lines (not mine, but mine looks very similar). I followed these directions and they worked! GL.
 
73 Paula k9ir

From: John King <k5pgw at yahoo.com>
To: "Heath at puck.nether.net" <Heath at puck.nether.net> 
Sent: Wednesday, January 9, 2013 8:44 PM
Subject: [Heath] SB 200 Parasitic chokes


Has anyone changed the parasitic chokes on their SB 200s. I need to change mine because the leads to the chokes are breaking off at the resistors. Has anyone tried chokes made width ferrite beads on wire leads as parasitic chokes? If so how many beads and what mix and size? The 47 ohm 2 watt carbon composition resistors are not available locally and neither is the tinned wire to wind around them. The area around the tube plates doesn't leave much wiggle or working room. What has been your experience with the SB 200? Thanks and 73, John, K5PGW  

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