[Hallicrafters] My First Boat Anchor Restoration: SX101 MkIII

Tue Nov 15 22:49:03 EST 2011

Two very fine signal generators are the General Radio 1001-A and the military URM-25 series, both of which will go down to 50 KHz.  The GR generator is big and not-too-heavy but because of its size, many people turn up their noses at it.  The URM-25 can be pricey because that's the one most everyone wants; and they often need some restoration before they can be used.

The military BC-221 and LM-series heterodyne frequency meters make excellent signal generators; but they only go down to 125 KHz (some early LMs only go to 195 KHz).  These units are only "calibrated" to 20 MHz on HF; but don't despair.  They are perfectly usable to at least 54 MHz on harmonics.  They are very stable and highly accurate.  And they are plentiful and CHEAP.

73

Mike
W4DSE

--- On Tue, 11/15/11, Jason Hissong <jhissong at gmail.com> wrote:

> From: Jason Hissong <jhissong at gmail.com>
> Subject: Re: [Hallicrafters] My First Boat Anchor Restoration: SX101 MkIII
> To: "T David Cohen" <tdavid at eatel.net>
> Cc: hallicrafters at mailman.qth.net
> Date: Tuesday, November 15, 2011, 2:58 PM
> Dave,
> 
> Thanks for your email.  My dad gave me an HP 5302A a
> while back that
> was collecting dust in my closet.  I finally pulled it
> out to use it.
> A V7A is on the way (got it for 21.00 on EBay, just needs a
> DC probe
> which I will build).
> 
> As for a signal generator, I will look for one and make
> sure it can do
> at least 50Khz.
> 
> Jason
> 
> On Tue, Nov 15, 2011 at 1:37 PM, T David Cohen <tdavid at eatel.net>
> wrote:
> > Jason,
> >
> > Good luck with your "restoration" project.  The
> SX-101 is a great receiver
> > (as long as you don't have to move it very far).
> >
> > If you're going to do any significant troubleshooting,
> you'll need a
> > suitable meter.  For the most part a VOM is OK when
> you're measuring B+,
> > line voltage or filament voltage.  Where a VOM
> becomes a problem is when
> > you're trying to measure voltage in a circuit where
> the input resistance of
> > the meter itself imposes a significant "load" on the
> circuit you're trying
> > to measure and that load has an impact on the
> operation of the circuit.  An
> > example might be measuring the grid bias on a tube
> circuit. Sometimes the
> > voltage source you're measuring is current limited
> (maybe passes through a
> > high value resistor) and the load imposed by the VOM
> will give inaccurate
> > readings.
> >
> > The solution to the problem is the VTVM.   The vacuum
> tube in the VTVM
> > imposes a VERY SMALL load on the circuit it's
> measuring and consequently, it
> > has almost no effect on the circuit being tested.
>  Fortunately, you can find
> > very capable VTVM's on eBay for practically nothing.
>  The Heath V-7A is a
> > great meter and I think the equivalent Eico instrument
> is the 232.  If you
> > watch the auctions, you can probably get one for $20
> including shipping.
> > The HPs are very nice in an old sort of way but are
> expensive unless you
> > just want one.
> >
> > If you've got some money to spend, a new digital meter
> is a good bet.  Make
> > sure the input resistance is > 10 megohms.  The
> down side of one of these
> > new meters is that they are inconvenient when used as
> output indicators
> > during an adjustment process (an i.f. alignment for
> example).  There, the
> > trend you can easily visualize on an analog meter is
> missing.  As the
> > sampling rate goes down, the problem becomes worse.
> >
> > You'll probably want a signal generator.  You can
> find cheap ones on eBay.
> > The problem you face with Hallicrafters receivers (and
> some others too) is
> > the 50 kHz second i.f. frequency.  Most common signal
> generators don't go
> > that far down so your choices become limited (actually
> Hallicrafters made a
> > signal generator just for that very purpose).  The
> military surplus URM-25s
> > work fine but a rebuilt one (and almost all of them
> need a thorough going
> > through) is going to be fairly expensive.   Another
> one that you can find
> > from time to time that works fine for old tube gear is
> the Aul Instruments
> > SG-1144u (they have their problems too -- particularly
> the power supplies).
> > The SG-1144's when they are working are very stable
> solid state generators
> > and are a real asset if you're working on old
> receivers.
> >
> > Finally, a counter might be helpful.  They do a great
> job is setting up
> > signal generators AND I use 'em all the time to check
> the output frequency
> > of local oscillators in receivers.  They make
> alignment MUCH easier.  Here
> > I'm partial to used HPs.  They work great, are
> inexpensive and are fairly
> > easy to find.  The Chinese alternatives you can find
> on eBay work fine too.
> >
> > Again, good luck with your project.
> >
> > Dave Cohen
> >
> >
> > -----Original Message-----
> > From: hallicrafters-bounces at mailman.qth.net
> > [mailto:hallicrafters-bounces at mailman.qth.net]
> On Behalf Of Jason Hissong
> > Sent: Tuesday, November 15, 2011 10:51 AM
> > To: rbethman
> > Cc: hallicrafters at mailman.qth.net
> > Subject: Re: [Hallicrafters] My First Boat Anchor
> Restoration: SX101 MkIII
> >
> > Glad I mentioned the meter I had.  Looks like I need
> to find a VTVM like a
> > Heathkit or an HP previously mentioned.
> >
> > So much to learn!  It is a different world.
> >
> > Jason N8XE
> >
> > On 11/15/11, rbethman <rbethman at comcast.net>
> wrote:
> >> Pay careful attention to the MANUAL!
> >>
> >> AC is read with a 1000 Ohm/Volt meter!  DC is
> read with a VTVM!
> >>
> >> There is a BIG difference.
> >>
> >> The B+ is 280VDC.  It will bite you worse than
> 120/240 VAC!  DC WILL
> >> cause the muscle(s) to clamp down.  If you get it
> in the palm, and are
> >> grounded, you will NOT be able to let go!
> >>
> >> This is different than AC.
> >>
> >>
> >>
> >>
> >
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