[Drake] Multimeter Suggestions for Drake Service

[Garey Barrell]

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
>
>