Topband: Re: Vactrols and Flag

[Mike Knowlton]

  On my Flag I used a VTL3A27 that I got from Steve Byan.
I got a range of 390 ohms to 1450ohms by using the following.
I put a 1,330 ohm resistor in Parallel with the photocell---then a
300 ohm resistor in series with the parallel resistor and photocell.
  Second at my control box I put a 270 ohm resistor in series with
the bulb, I used a 500ohm variable resistor to control the brightness of =
the
bulb. I used a 12 V supply. The 270ohm resistor limits the
current to my bulb, I did that to extend the life. If you want your
termination to go lower just reduce the 270ohm resistor.
  The temination control does tighten up at the high end, I had a
note to install a 50ohm fine tune pot in series with the 500ohm control =
pot
but I never did, it wasn't that tight. A ten turn pot
would give you a fine tune.
  The resistor values are a bit strange because I had a box of surplus =
1%
tolerance resistors. I think standard values will get
you a good termination range.
   While writing this letter I did a web search and saw a couple of =
notes
saying the VTL3A27 is no longer available, If that is true, I
think the parallel/series combo is useful to give you the range you want
with several of the vactrols available.
  I was very pleased with my rotatable variable termination flag, I use =
it
mostly for BCB. It was neat to turn the termination control
and listen to the offending station go into the noise.
 Did I say -was- , yes about two weeks after getting the antenna
up it rotated on the mast and broke my control wire. I'll be getting
it fixed soon. I have some pictures on  my web site, take a look.
                   http://home.att.net/~amdx/
  I also have a question about rotating the Flag vertically for repairs
and mods. It's detailed on the web site.
                                          Mike Knowlton

                   http://home.att.net/~amdx/




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