[ARC5] BC-230 Transmitter- 5-6 MC Coil on 40 Mtrs

[David Stinson]

The 5-6 MC tuning coil for the BS-230 / -430 transmitter
is easy to non-destructively "tweak" to 40 meters.

First check:  Neutralization Coil Continuity.
Neutralization coils are open on about half of these coil sets.
It's the little coil form inside the PA/ANT coil.
I don't know what kind of wire they used to wind it, 
but it decays and goes open.  The winding will often
litterly crumble off the form.

Check for continutity (can be 15-40 Ohms or so) across
these two terminals:
http://home.netcom.com/~arc5/SCR-183/neut1.jpg
If it's open, scroll down and fix this first.}
Don't try to use the transmitter with a proper 
neutralizing coil.

We move the Oscillator coil (the shielded one) to 7MC
by moving the top coil connection down four turns:
http://home.netcom.com/~arc5/SCR-183/5-6OscCoil.JPG
You will need a really hot soldering iron.  The coil form
wicks-away a great deal of heat.  I scraped the wire for 
the new tap so it would tin.  This needed so much heat,
I pulled the tip off my Weller and pushed the two 
ends across the wire, effectively making the coil wire
the heating element.  That made it take solder quickly.
The Osc. should now cover all of 40 meters in the 
range of 2000 on the freq control calibration.

I haven't found any need to change the PA/ANT coil.
Perhaps you'd get a little more power out if you move
the PA tap down and turn or two but I haven't done this.
Set the "tapping wheel" eight positions up from the bottom:
http://home.netcom.com/~arc5/SCR-183/5-6PACoil.JPG
In my transmitter with original tubes (VT-25, -52), I get 
a little over 3 Watts out with a "stiff" 330 VDC supply.
It will have a little chirp.  
If you want crystal control, it's easy to do.
You need a good, active FT-243.
----------------------------

If your neutralizing coil is open:
You'll have to rewind it.  It's not as hard as it seems.
The coil form (inside the PA/ANT coil form) is fragile.
Don't panic if you break it ( I"ve broken a few and
broke the one in the photos).  The form takes glue fine.

Remove the PA/ANT coil from the mount and its
black base.  Mark the "top" and "bottom" terminals- 
"bottom" being the wire nearest the mounting rods-
from the Neutralizing coil as shown in the photo.
"Bottom view:"
http://home.netcom.com/~arc5/SCR-183/NCoilRepair1.JPG

The support rods are soldered at their juction.
No matter how hard you try, you aren't going to be
able to remove every bit of that solder.  You can't 
just unsolder the support rods and try to pull them
straight out.  The added diameter of the solder coat
will break the form.  Carefully cut-out the junction
and pull the rob pieces *inward* to remove them.
Don't panic if the fragile form breaks.  You'll note
I broke this one.  It takes glue well.
Once you unsolder the wires and pull the rods out,
the small form will come out the "top" (non-terminal)
end of the PA/ANT coil.  

Count the number of turns.  Mark the Neutralizing coil form
 with the winding direction, start and end points and 
the number of turns:
http://home.netcom.com/~arc5/SCR-183/NCoilRepair2.JPG
This one had 14 turns.
Remove the rotten wire.   Rewind the coil with any good
enamalled wire.  You don't need to get it "perfect."  
Space it to full the area of the original coil.  
http://home.netcom.com/~arc5/SCR-183/NCoilRepair3.JPG

Drop the coil down through the top of the PA/ANT coil.
Turn the mounting rod pieces around, clipped-ends 
out and run them back through the holes so they hold
the little coil form in place.  Give them a daub of hot glue
or silicon to hold them.  Resolder the wires to the terminals
and reassemble the coil.