[Heath] More SB-200 joys...

[Kenneth G. Gordon]

On 13 Jan 2012 at 22:15, gjcollins at cox.net wrote:

> Where can I find the details on Carl's SB-200 parasitic suppressors? 
> A quick search didn't locate anything on-line.

Hello, George:

I don't think they are on line. I got the info directly from Carl. He 
modifies SB-200s for 6 meters, and does a LOT of repair, 
refurbishment, and mod of other amps.

> I'm just finishing up a rehab of a SB-200, so your posts have been
> very interesting.

Thank you. I was hoping some of my info would help others.

OK.

Here is how you make the parasitic chokes:

Buy some 100 pfd 1KV mica caps, and some 50 ohm 5 watt MOX resistors 
from Mouser or your supplier of choice. I can supply part numbers if 
you need them.

Get some perf board and mount the parts on it in the following 
manner:

               4 turn coil 
HV<_____()()()()_______>TUBE PLATE
  100pfd_|_        _|_100pfd
                T           T
                 /\/\/\/\/\/\/\
                 50 ohms

I hope the above is clear...

In words:

Build a Pi-filter. 

Use the original coil, or wind a new one of 4 turns, #18, #16, or #14 
solid copper wire. I preferred to wind a new one of exactly 4 turns 
out of #14 wire.

Connect ONE lead of each capacitor at opposite ends of the coil. 
There should be one lead of each capacitor connected to opposite ends 
of the coil and the other lead of each capacitor should not be 
connected to anything at this point. 

Connect the OTHER LEAD of each capacitor to one of the ends of the 
resistor. There should be one of the remaining (free) leads of each 
capacitor connected to opposite ends of the resistor.

Or to explain another way, the resistor should be in parallel with 
the coil, and there should be a capacitor connected between the coil 
and resistor at each end. The whole should form a rectangle with the 
caps forming the ends and the coil and resistor forming the top and 
bottom. The turns of the coil should be spread so that the coil is as 
long as the resistor.

Mount all parts on a bit of perf board.

Since these chokes are larger than the original ones, you will have 
to mount one choke ABOVE and to the RIGHT of the LEFT tube, and one 
choke BELOW and to the LEFT of the RIGHT tube.

Keep all leads as short as you possibly can.

I'll be happy to send photos of the chokes and how I mounted them to 
any interested party if needed.

Ken W7EKB