[Milsurplus] BC-221 types

[J. Forster]

I'll look at the voltages next time I have the thing open, but if it was
something in the tube, wouldn't the effect be larger on the high band?

-John

==============


> Looking at the schematic again I see that the capacitor I suspected
> is actually the bypass capacitor for g2+g4. Agree that it seems unlikely
> that bandswitching would affect the triode RF characteristics much as
> a result of this capacitor's failure.
>
> A simpler mechanism that occurs to me is that the tubes are oscillating
> more strongly on the lower band, hence drawing more current on average,
> and this results in different DC operating characteristics for low vs high
> range.
>
> 73, ian K3IMW
>
>
> On Mon, Jul 29, 2013 at 11:31 AM, J. Forster <jfor at quikus.com> wrote:
>
>> When you say 'gone bad' what do you mean? Open? Leaky? Short?
>>
>> If you look at the print, only LC components are bandswitched.
>>
>> -John
>>
>> =============
>>
>>
>>
>> > 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
>> >> >
>> >> > ______________________________________________________________
>> >> > Milsurplus mailing list
>> >> > Home: http://mailman.qth.net/mailman/listinfo/milsurplus
>> >> > Help: http://mailman.qth.net/mmfaq.htm
>> >> > Post: mailto:Milsurplus at mailman.qth.net
>> >> >
>> >> > This list hosted by: http://www.qsl.net
>> >> > Please help support this email list: http://www.qsl.net/donate.html
>> >> >
>> >> >
>> >>
>> >>
>> >> ______________________________________________________________
>> >> Milsurplus mailing list
>> >> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
>> >> Help: http://mailman.qth.net/mmfaq.htm
>> >> Post: mailto:Milsurplus at mailman.qth.net
>> >>
>> >> This list hosted by: http://www.qsl.net
>> >> Please help support this email list: http://www.qsl.net/donate.html
>> >>
>> >
>>
>>
>>
>