It's a pretty good bet that most RF Cafe visitors are not overly interested in
vacuum tube testers. Today they are collectors' items with some actually still being
used for maintaining vintage electronics gear; however, in the days before semiconductor
components they were the life blood of service men. Because tubes (aka "valves"
in other parts of the world) are by nature one of the most vulnerable parts of any
product in which they are used, often the first step in troubleshooting a radio,
television, record player, etc., was to test suspected tubes for sub par performance.
As mentioned often in
Mac's Radio Service Shop stories, customers balked at service centers charging
for their expertise but didn't mind as much paying for replaced components. That
meant mark-ups on vacuum tubes comprised a large percentage of profit - which still
wasn't all that much - for a service job. Electronics magazines of the era carried
advertisements from multiple companies offering vacuum tube testers varying in complexity
from versions which only worked for some of the most common part numbers to ones
like those shown here in a 1955 issue of Radio & Television News that
could check almost any tube made.
When servicing in the home, time is money; these tube testers save service time.
The two tube testers shown here check all of the popular tubes
used in radio and TV sets. On the left is the B&K "Dyna-Quik." the one below
is by TeleTest.
Every service technician, whether he works for himself or someone else, is always
running a race with the clock. Time is truly valuable and any instrument which permits
a necessary job to be done more quickly than before, without impairment of accuracy,
will always be of interest to the service industry.
"Dyna-Quik" Model 500 Tester
An instrument which is designed to speed up tube testing is the "Dyna-Quik",
Model 500 tester, manufactured by the B & K Manufacturing Company of Chicago.
This instrument is portable and operates on the Gm principle. It contains
30 sockets and will test close to 400 different types of tubes. Each socket will
check only the specific tubes which are listed for that socket. The test procedure
is to first locate the proper socket for a tube. At the bottom of the instrument
panel there are two controls, labeled "Heater" and "Sensitivity." The proper settings
for these controls are indicated with each tube listing. Once the controls are set,
the tube is plugged into its socket, a "Test" button is depressed and the condition
of the tube is revealed on the large 4 1/2 inch meter. The three indications are
"Good," "?," and "Replace."
If desired, the exact mutual conductance value of each tube can be obtained by
setting the "Sensitivity" control according to a separate chart attached to the
inside of the front cover. In addition, this instrument will also reveal gassy tubes,
tubes with grid-to-cathode leakage, and tubes having contaminated grids. Tube shorts,
between heater and cathode, grid and cathode, grid and screen, or grid and plate,
will automatically light up a neon bulb. Another automatic feature of this instrument
is its line voltage regulator circuit. This maintains test voltages constant over
power line variations from 105 volts to 125 volts.
An interesting feature of the Model 500 is the provision made for keeping the
socket panel plate up-to-date. The designers of this instrument recognized that
new tubes are appearing constantly and a tube tester must keep abreast of these
changes if it is to retain its usefulness for any extended period of time. To meet
this situation, a new overlay plate will be prepared whenever a significant number
of new tubes has been developed. The instrument owner will then be able to obtain
this plate for a nominal charge and use it to cover the original plate.
The Model 500 "Dyna-Quik" tester is specifically designed to be taken into the
house where a rapid check of all receiver tubes may be made. In this respect it
will not only pinpoint tubes which are definitely bad, but a special life test will
also reveal those tubes which are on their way to becoming defective. By calling
the latter tubes to the set owner's attention, callbacks can be significantly reduced,
Tele Test T-56 Checker
Another rapid testing tube checker is the TeleTest T-56 instrument. This contains
60 sockets and is equipped to check a wide variety of receiving tubes as well as
picture tubes and selenium rectifiers. In addition, continuity can be tested in
circuits having resistance as high as 1 1/2 to 2 megohms. If continuity exists,
a neon bulb will light up. If more than 2 megohms of resistance is present (and
this includes an open circuit), the bulb will remain unlit.
The manner in which the TeleTest Model T-56 is used for its main purpose of checking
tubes is quite simple. All of the tubes which can be tested in this instrument are
listed on a tube chart which is fastened to the inside of the top cover of the carrying
case. The first column after the tube type contains the etter indicating the setting
of the "Filament" switch. The second column contains the number of the proper test
socket on the panel of the tester. The third column contains the number that indicates
the section to be tested.
The fourth column has the "Reference" number or meter reading for that tube type.
If a tube has only one section, there will be only one section setting and one reference
number. A tube can have as many as four sections. In the event that the tube has
more than one section, there will be a separate section number for each section
and a separate reference number.
The reference number refers to the meter scale. This scale is divided from 0
to 100. In checking a tube, if the meter reads on or below the reference number
for that tube, it can be considered faulty and should be replaced. For a tube to
be considered good, the meter should read above the reference number.
Just beneath the indicating meter there are three neon bulbs. Inter-element shorts
automatically light one of these bulbs prior to the test of the tube or section
of the tube. Heater-to-cathode shorts are revealed by the lighting of one of the
other neon bulbs. The third bulb lights .up when a tube is gassy, or there is grid
emission or there is less than the desired resistance between grid and cathode.
(The latter is sometimes referred to as a high resistance grid short, which is obviously
a misnomer, or as grid leakage.)
Either of the foregoing tube testers may be used in the home (their primary purpose)
or they may be used in the shop. In the latter place it has been suggested that
customers be permitted to check their own tubes, when these are brought in. It has
been found (surprisingly enough) that when a customer checks the tubes himself,
he is more likely to replace all those showing up 'bad, Whatever the psychology
behind this, the service technician benefits two ways. First, he sells more tubes.
Second, he does not lose 20 to 30 minutes checking tubes.
Posted October 26, 2020