82 What sort of tools and test equipment do I need.
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This article is from the Antique Radios And Phonographs FAQ, by Hank van Cleef vancleef@netcom with numerous contributions by others.
82 What sort of tools and test equipment do I need.
A 20,000 ohms/volt multimeter is indispensible. They are relatively
inexpensive, and modern multimeters have protection circuits in them.
You can trouble-shoot and fix almost anything discussed in this
newsgroup with a multimeter and some knowledge of circuit theory. Many
prefer an analog meter with a needle over digital. You can watch the
needle move and see what's happening.
While not "test equipment," tools for unsoldering and soldering
components and wire are also mandatory. Soldering is discussed in
another FAQ question.
Other small hand tools include screwdrivers, allen wrenches (for knobs
with setscrews), nut drivers, and small diagonal cutters and
needle-nosed pliers. There is only one kind of tool, a good quality
tool. Buy the best. They'll last forever, and do their jobs well.
Don't buy cheap knucklebusters. They are hard to use, will make
scratches, bend, and break, and scar up the work. Buy the best---many
of the good tool manufactures have sold the same tools for over fifty
years, and many of us use tools that old today.
Beyond the basics are the following:
a. Oscilloscope. This has become the primary instrument for use in
electronics work of all sorts. While they were not commonly used for
radio repair in the 1930's and '40's. There are a great variety of
scopes, ranging from the old relaxation oscillator sweep type used in
the thirties (and sold by Heath as late as the 70's) to the very latest
solid state scopes with triggered delaying sweep and multiple trace
vertical inputs. Almost any scope that works is fine for working on old
radios and vacuum tube amplifiers. While you can get old vacuum tube
scopes for very low prices, keep in mind that you may find yourself
trouble-shooting and fixing it.
b. RF signal generator. Once again, these come in many sizes and
shapes. These are used for aligning tuned circuits (RF and IF
amplifiers). For an AM-shortwave radio, you need 100 kc. to around
15-20 mc, with AM modulation capability, and for FM, you should have
88-108 capability as well. A sweep signal generator (i.e., able to
swing the frequency back-and-forth over a small range electronically,
with a voltage output to drive an oscilloscope horizontal amplifier) and
a suitable scope are very nice to have but not mandatory.
c. Tube tester. The value of tube testers as a primary diagnostic tool
tends to be overrated, but a good mutual conductance tester (Hickock
made several) can be of value if it is used appropriately. Cheap "tube
checkers" will test filaments (an ohmmeter will do as well) and whether
the tube conducts or not, and may detect hard short circuits (these do
happen). A Tektronix 570 curve tracer (a specialty oscilloscope that
gives graphic displays of tube characteristics) is the ultimate in test
devices. However, the ultimate "tube tester" is the equipment in which
the tube is used. The function of tube testers, more than anything
else, was to sell replacement vacuum tubes. And many really nasty
tube-related problems will only show up in the socket in the equipment
where they are supposed to function properly.
If you have a good scope, multimeter, and signal generator, and know how
to use them, you have all the tools you need for radio work. Here are
some other items, some of which were popular as radio shop tools, and
some of which aren't primarily test equipment.
d. Signal analyzer, signal tracer. These were very popular in radio
shops. They are an AF amplifier, small speaker, and a diode detector
that can be switched in and out of the probe circuit---in essence, a
small radio without any tuned circuits. If signal is getting into the
antenna, you can probe each stage and hear it, and quickly locate a
"dead" or "distorted" stage.
e. Condenser tester. Also "radio shop" stuff from the 1930-50 era.
An inexpensive L-R-C bridge with an electronic oscillator. Used
properly, it can be a handy tool. I use the term "condensor" because
it was the standard term for a "capacitor" in the US until the late
1950's.
f. VTVM (stands for "Vacuum Tube Voltmeter"). The virtue of these is
the high input impedance (generally megohms) and their ability to
measure resistances into the megohms range. Largely supplanted by
oscilloscopes, which draw a picture of the signal, but of value today
for their ability to measure high resistance.
g. Grid dip meter. This is a small oscillator that comes with a set of
plug-in oscillator coils that can be poked into tuned circuits. They
rely on the fact that a resonant circuit near the oscillator coil will
cause the grid current of the oscillator tube to drop, hence "grid-dip."
A very simple and handy little device, though generally used with things
like transmitters that have to be tuned before power is applied. Since
they oscillate, they are also a fine "poor man's signal generator."
There were several specialty houses in the US in the 1930-50 era that
built very good measurement equipment. I'll mention them by name:
Boonton Radio, built Q-meters and R-X bridges. These measure the
inductance and other characteristics of RF coils and tuned circuits.
Generally used to support coil design efforts. The British Marconi
Q-meters are excellent as well.
Measurements Corp. Built very nice signal generators, much higher
quality than those from repair equipment manufacturers like Hickock.
General Radio (Cambridge, Mass.). This company moved to the suburbs in
the late 1950's and is now known as Genrad. Their 650 impedance bridge
was the general use DC/400 cps L-R-C bridge. It used a small battery
and a 400 cps "hummer" (a small vibrator) to generate AC for measuring
impedance of things like audio transformers. Over the years, General
Radio built a broad line of devices, primarily for engineering use, only
some of which are applicable to radio electronics.
Guildline of Canada. I mention them because they built some of the very
best calibration standards. Their potentiometers and other products are
not only "not test equipment" but can easily be damaged if used for
testing things. The proper use of such equipment is calibration of
working equipment, and the appropriate place for it is a calibration
shop.
While I mention equipment common in the US, I am familiar with products
of Marconi in England, who built engineering support products similar to
the Boonton, Measurements, and General Radio products. I believe that
Telefunken, Phillips, and Thompson-CSF (spelling?---French company) also
built and sold similar equipment. The US stuff often shows up at things
like ham swapfests, and is bought and sold by several companies, notably
Tucker, of Dallas, Texas.
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