[Drake] Multimeter Suggestions for Drake Service

Tue Dec 7 15:28:43 EST 2010

Very good advice, Garey. It's a shame so many hams are unfamiliar with the
benefits of using a calibrated oscilloscope (and I couldn't agree more about
your view of most Heathkit oscilloscopes). With a good scope, one actually
doesn't need _any_ other voltage measuring instruments. 

The only thing I'd add to your comments is that, for most ham use, an analog
scope is preferred over a digital scope. Prices have really come down on
excellent analog oscilloscopes in the past few years. In the opinion of
many, the very best analog scope ever made was the Tektronix 2465B, and one
can pick up one in excellent condition for about $400 (new cost was about
$10K). Lesser scopes (which are perfectly appropriate for 99% of ham use)
cost proportionately less.  Over the weekend, a ham buddy brought over a B&K
40MHz scope that he bought for $15 at a hamfest. A few spritzes of DeOxit on
the rotary switches and it worked just fine, with excellent calibration and
very stable triggering.
73,
Jim W8ZR 

> -----Original Message-----
> From: drake-bounces at mailman.qth.net [mailto:drake-bounces at mailman.qth.net]
On
> Behalf Of Garey Barrell
> Sent: Tuesday, December 07, 2010 12:51 PM
> To: Drake
> Subject: Re: [Drake] Multimeter Suggestions for Drake Service
> 
> Richard -
> 
> The key to the multimeter is input impedance.  Ultra-precise voltage
> readings are never really required to service our gear.  Aside from
> Collins or other government supported manufacturers, most repair and
> even design work of Ham gear was done with Heathkit class VTVMs.  Every
> once in a while someone would spring for an RCA VoltOhmyst, but not
> often!  As for reading voltages to two (or three!) decimal places, I
> can't think of a single place where that is necessary.  The only thing
> that comes close is the Drake receiver Sensitivity or AVC threshold
> specified as -1.35 VDC, and it tends to wander a couple of tenths over
> temperature, etc., so not REALLY all that tight.
> 
> The Heathkit IM-11 / IM-18 etc., are perfectly suited.  The better
> commercial equipment such as the HP 427 VTVM and up is great, and
> certainly built to a higher standard.  Some of the HP meters had
> individually printed meter scales for improved accuracy.  They are nicer
> mechanically, are a pleasure to use, and many have come down to a
> reasonable price since just about all commercial test is computer
> controlled these days.  But for our use, there really isn't anything
> better than an IM-18 from a FUNCTIONAL standpoint.
> 
> My second purchase would be a scope.  Here the opposite is true.  All
> but one, or maybe two, of the Heathkit scopes aren't worth the trouble
> to carry them home.  For a scope to be useful, it really needs to be
> 'calibrated', both in time and amplitude, and have 'triggered sweep'.
> Anything else is a frustrating waste of time and energy for anything
> beyond Lissajous or sine wave displays.  They do make good SSB
> modulation monitors with modification, but as a lab scope, no thank
> you.  Here you want to find a good used Tektronix 2215A, 465B, 454A,
> etc. unit.  You can get any one of them for $100-150 if you're patient.
> The surplus labs that refurb and calibrate them to NBS standards cost
> quite a bit more, but they all show up from time to time on the usual
> places at very reasonable prices.  With a good scope, you'll find you
> reach for it FIRST about 90% of the time.  (Remember, it's 'calibrated'
> and with a single touch of a probe you can not only tell if a power
> supply is working and the correct voltage, you can also see just how
> much ripple is present.)
> 
> After the scope, I'd get one of the NORCAL or Elecraft signal
> generators.  They're about the size of an Altoids tin or smaller, and
> generate a calibrated 1 uV and 50 uV signal on a single, crystal
> controlled frequency on the 80, 40, 30 and 20M bands.  The Elecraft is
> only 80, 40 and 20M.  This is all the signal generator you need for
> testing, repairing and even calibrating S-Meters on our stuff, at least
> on those three or four bands.  Wide range, continuous coverage,
> calibrated signal generators are nice, but you'll find that you don't
> use them often.  In a pinch you can always use your modern transceiver
> as a source.  The receiver portion of it also makes a fair spectrum
> analyzer or signal tracer.
> 
> Lastly, I'd invest in one GOOD Fluke DMM to use as a reference source
> for calibration of all the above.  Take care of it and keep it in a safe
> place.  If you want/need a DMM for the car or yard or on the bench, the
> little Harbor Freight $2-3 meters are ok with one caveat.  They have a
> LOW input impedance (~1 Meg) which will mislead you on some tube grid,
> AVC, or other high impedance circuits.  The VTVM is 11 Meg, and is
> hardly ever a loading risk.  A good scope probe (10x) is also 10 Meg.
> 
> Beyond this you're looking at convenience, preference, and how much
> money you want to spend.  But if you have the above, you'll be able to
> do just about anything you need to do!
> 
> 73, Garey - K4OAH
> Glen Allen, VA
> 
> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
> and TR-4/C Service Supplement CDs
> <www.k4oah.com>
> 
> 
> Richard Bell wrote:
> > I know we've been down this path before, but I don't seem to remember
the answer.
> >
> > What would be a good multimeter to be used for servicing our beloved
Drake gear?
> >
> > I know some with say a old school VTVM from Heahkit.  Others will say
buy a Fluke.
> >
> > I'm trying to get the retirement test gear in order before I have no
funds for this sort of
> journey.
> >
> > Feel free to email me off the list, richfbell at sbcglobal.net, if you
desire.
> >
> > TNX&  73 W5BXE
> >
> >
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