Founded in 1921 in Salem,
started out making vacuum tubes, then after being bought by
CBS (Columbia Broadcasting
System, the TV broadcasting people) in 1951 they moved into the realm of
semiconductor production. This story from a 1944 issue of Radio News
magazine extolled the virtues of Hytron's Master Test Station for its ability to
quickly and accurately measure a wide variety of tubes. Auto-ranging voltage
regulators, parallax-free meters with auto-ranging scales, safety fusing, and
easy servicing were among it notable features. To me, a parallax-free meter is
one with a mirror behind the needle used to assure the operator is looking
straight-on at the scale, but in this case it meant the array of meters was
arranged in a semi-circle so that the operator was naturally looking
perpendicular to the meter faces from a fixed vantage point. The level of
automation no doubt reduced measurement errors and allowed a less skilled
operator at the test tstation.
Here is an interesting reproduction of a pamphlet published by CBS-Hytron in
1954 highlighting their "modern"
tube production facility.
Deluxe test console for production testing miniature to medium-power transmitting
The versatility of this test unit permits highly accurate measurements
of the major characteristics of many types of tubes.
By Harry G. Burnett
Dissatisfaction with the limitations of previous kits for production and quality
testing of vacuum tubes, led Hytron engineers to design a master test kit which
incorporates many features. Flexibility, simplicity of operation, automatic electronic
fusing, automatic electronic switching of meter ranges, sufficient power supplies
- all voltage-regulated, avoidance of parallax, standardized components, and ease
of serviceability were incorporated into the master test station illustrated.
The scope of possible measurements is highlighted in the accompanying table.
For the sake of simplicity, only the over-all ranges are shown, but the choice of
ranges for a given measurement is wide. For example, plate current ranges are as
follows: 0-10-20-50-100-200-500-1000 ma. If necessary, external meters can be patched
into the circuits for even greater diversity.
One of the most interesting features of this deluxe test console is the automatic
range control for voltmeters. If the applied potential is increased beyond the range
of a given meter scale, a thyratron and associated relay automatically switch in
the multiplier for the next higher range. Simultaneously a pilot lamp on the instrument
panel lights over the appropriate full scale value engraved on the panel.
Scope of Possible Measurements Hytron Master Test Station
*A supplementary power supply may be switched in to extend range to 1500 volts.
Each section of multi-section tubes may be measured separately. Dynamic measurements
of rectifiers and converters are made on separate apparatus, because they present
such different problems.
Another novel electronic application is the fuse protection for all current meters
except filament current meters (these are conventionally fused). This electronic
fuse protection is automatically changed for different ranges. An ingenious circuit
permits this same electronic protection even when the range of the measuring instrument
is less than the current drawn by the voltmeter itself. A completely shorted tube
may be inserted into the test socket without injuring a single instrument.
In designing this test station, the engineers incorporated voltage-regulated
power packs throughout. The only exception is a 14-volt storage battery (equipped
with automatic battery charger) for the lower d.c. filament potentials. The voltages
of these regulated packs are essentially constant from zero to maximum, because
a separate regulated pack supplies the control tubes. Once the test kit is adjusted
for a given type of tube, no readjustments are necessary as different tubes of that
type are plugged into the test socket. Two rheostats in the grid circuit of each
control tube permit both coarse and fine adjustment of the supply voltage.
A glance at the photograph of the test station, discloses the great care taken
to avoid parallax in reading the instruments. By placing the meters in a carefully
determined arc, and at the proper vertical heights, the eyes of an operator of average
height are correctly positioned, assuring greater accuracy in final operation.
Painstaking planning provided all controls within easy reach. Accessible drawers
are provided for adaptors, spare meters, headphones, and test records. A built-in
cathode-ray tube may be used as a visual null indicator for the vacuum tube bridge,
instead of headphones. Although not shown in the photograph, an adjustable fluorescent
lamp mounted on top of the test station, floods the instrument panel with ample
The automatic electronic fusing protection for current meters and the automatic
ranging of voltmeters make practicable the use of extremely accurate instruments.
Use of vacuum tube voltmeters instead of micro ammeters eliminates meter burnouts.
The v.t.v.m. is highly degenerated for stability, and adjusted for saturation above
the range in use, to protect the measuring instruments from damaging overloads.
The accompanying table indicates that meters have been chosen for 1/2 of 1% accuracy.
The test station, therefore, may be used as a standard for all other production
By means of patching cords, any meter or power supply may be connected into any
desired tube circuit. Supplementary supplies having ranges of 0-100 volts negative
and 0-1500 volts positive, can also be patched into chosen circuits. These features,
plus the wide meter ranges, allow full coverage from miniatures to medium-power
A wealth of controls is furnished for: switching from a.c. to d.c. filament operation;
adjusting of transformer primary voltages by transformer taps and by variacs; selecting
of proper circuits for heater-cathode voltage measurements; zero adjustment of vacuum
tube voltmeters; gain control of the bridge amplifier; switching on and off the
voltages applied to the 561D General Radio vacuum tube bridge; switching positive
or negative potentials to the grid; and varying the emission voltage between low
and high values.
It can be readily understood that Hytron's electronic equipment design engineer,
Ralph Thompson, and his engineering associates have lavished much thought on this
piece of equipment. The assurance of accuracy when the test kit is in operation
has repaid them many times for the midnight oil they burned in making their dreams
of a really modern and versatile test kit come true.
Posted March 30, 2021