[Hallicrafters] My First Boat Anchor Restoration: SX101 MkIII

[Jason Hissong]

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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