[Milsurplus] BC-221 types

[Ian Wilson]

I have seen the issue that John mentions also. My theory (I can't test
this since I don't have that particular unit any more) is that the cathode
bypass capacitor of the 6K8 - a .001uF Micamold I think - has gone
bad. Since the two cathodes of the triode-hexode are common, this
could affect the RF characteristics of the triode grid circuit.

73, ian K3IMW



On Mon, Jul 29, 2013 at 10:08 AM, J. Forster <jfor at quikus.com> wrote:

> I also have an -AK in a wooden case, but it has a very odd issue.
>
> On the high band, the unit is spot on.
> On the lower band, the COMPENSATOR does not have enough range to allow the
> dial and book settings to be matched.
>
> As nearly as I can figure, the horizontal, tubular ceramic inductor must
> have decreased in value, but I just don't see how that's possible.
>
> Any ideas?
>
> -John
>
> ====================
>
>
>
> > I have owned a number of BC-221 freq meters over the years.  If you have
> > a calibration book WHOSE SERIAL NUMBER MATCHES THE INSTRUMENT, these
> > meters are darn near on the money!  I have seen units before at hamfests
> > which had a cal book that been taken from another instrument.  Watch out
> > for that!  The great thing is that the frequency-determining components
> > of these meters are 100% mechanical -- a wax-coated coil and a variable
> > cap milled out of a piece of brass.  Unless there has been physical
> > damage to the meter, it should be within a few Hz of WWV.  I have put a
> > number of the crystals in these units  up against WWV and could barely
> > detect a low-frequency beat note.  The only unit I currently have is an
> > AK model in a lightweight TS-164 aircraft housing.  There's enough room
> > in the back of the TS-164 to build a solid state power supply which puts
> > out 135V at about 20 mA and 6.3V at about an amp.  Watch out for paper
> > caps in these old units - they are notoriously failure-prone - including
> > the 'molded paper caps' that masquerade as micas.  The oil-filled
> > bathtub caps are probably OK unless they're leaking.  Oh, BTW, you
> > really need to use a (relatively) high-Z headset like an HS-30 with
> > these meters.  You won't hear anything if you plug in a modern 8 ohm
> > headset.  Hallicrafters made a tube-type AC supply called the RA-133
> > that fits in the back of one of the big metal-cased BC-221s
> >
> > Here's the definitive reference for the entire series of BC-221 freq
> > meters:
> >
> >     http://w5jgv.com/downloads/BC-221_SCR-211.pdf
> >
> > The half-tone photos aren't too readable, but the book is invaluable for
> > anyone interested in BC-221s.  I've also seen the book (TM-11-300) turn
> > up from time to time on E-Pay.
> >
> > I love these old meters.  Over the years, I've rebuilt and refurbished
> > more than I can remember, including replacing some really badly-hacked
> > homebrew AC power supplies.  I'm sort of a sucker when I see one sitting
> > neglected under a table at a hamfest. They may be 70 years old, but
> > they're still nice to have.  You can't put a receiver on frequency with
> > a counter!
> >
> > If you'd like to have a copy of the pdf for the RA-133 power supply and
> > the TS-164 aircraft housing, please email me direct.
> >
> > Hope this all helps ...
> > Mike, WB0LDJ
> > mharmon at att dot net
> >
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