[Hallicrafters] My First Boat Anchor Restoration: SX101 MkIII

Wed Nov 16 08:45:06 EST 2011

The URM-25D hung from one of my hands for about 3 years as a USN ET and it 
did an excellent job keeping our country safe.

National had the GR 1001A's and they drifted so bad we used discrete crystal 
oscillators to do calibration. The only thing they were good for was IF and 
filter alignment along with general tracking and spot sensitivity tests. The 
coax adaptors can get pretty pricey also and signal leakage can be a problem 
when doing sensitivity measurements on the better receivers.

With the NCX-3/NCX-5 and HRO-500 they were useless.

The HP-606A replaced them and it is still one of the best generators even 
today. I have a pair of them and save the fragile 8640B for other work.

Before getting the 606A's I rebuilt a URM-25D and used that for many years. 
They drift a bit but certainly not as bad as the GR.

A good 25D will run $50-100 unrestored and around $40-75 for a 606A from 
what Ive seen at New England hamfests and several forums. Ebay is usually 
much higher.

Carl
KM1H

----- Original Message ----- 
From: "Mike Everette" <radiocompass at yahoo.com>
To: "T David Cohen" <tdavid at eatel.net>; "Jason Hissong" <jhissong at gmail.com>
Cc: <hallicrafters at mailman.qth.net>
Sent: Tuesday, November 15, 2011 10:49 PM
Subject: Re: [Hallicrafters] My First Boat Anchor Restoration: SX101 MkIII

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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