The New G-10 Germanium Dot Rectifier
Engineering data on a new unit for radio, television, and allied power applications
which uses no critically-short materials.
By T. J. Ferguson
Crystal Eng. Sec., Comm. & Gov't. Equip. Dept.
Electronics Div., General Electric Company
Fig. 1. Over-all view of the General Electric germanium power rectifier which
has been designated the G-10.
General Electric Company has long been aware of the important characteristics
that make germanium rectifiers superior to other types of rectifiers. These characteristics,
are their lower forward resistance, higher back resistance, longer life expectancy,
and reliability. The advantageous characteristics of the germanium diode plus the
techniques for increasing the area of the rectifying surface, developed by the General
Electric Research Laboratories, have been responsible for a germanium rectifier
that could be used in television, radio, and allied power supply applications. The
G-E Germanium Dot Rectifier, designated G-10, having these characteristics, grew
out of this investigation. In addition, it was found commercially feasible to manufacture
the Germanium Dot Rectifier without the use of critical materials.
The G-10 is composed of two "button" rectifiers, each consisting of
a 1/8 square inch pellet of spectroscopically pure germanium placed in the center
of metal cups sealed with butyl rubber, as shown in Fig. 2. These rectifiers are
series mounted on two inch diameter, 1/32 inch thick metal dissipating fins. A high
coefficient of thermal conductivity is the governing qualification for the choice
of metal used in the dissipating fins. Copper and aluminum have been successfully
used. Production units will probably use aluminum dissipating fins.
Rectifiers are stabilized electrically by 24 hours of operation at full load.
This stabilization serves to remove the remaining gaseous impurities from the rectifying
surface and to relieve any mechanical strains within the button due to changes of
temperature with operation.
In order to insure an equal division of the peak back voltages across series-connected
rectifiers, it was found necessary to use units with the same dynamic back currents.
Any increase in temperature results in an increased back current. There are two
factors that vary from rectifier to rectifier that must be considered when selecting
rectifiers for their inverse currents. The first is the heat generated by the currents
in the forward and back resistance. The second is determined by the thermal characteristics
of the contact between the rectifier and the dissipating fin.
Both of these factors can be evaluated simultaneously by applying full forward
current during the selection test. Therefore, the rectifiers are sorted with respect
to their dynamic back currents at the full rated load. This sorting and selection
is done at the factory, hence the finished products are electrically stable and
only a very slight change occurs in the inverse current during the life of the rectifier.
Fig. 2. Cross-section view of one of the "button" rectifiers used in
the G-10 assembly.
To further insure that mismatched, damaged, or otherwise defective units are
not shipped to customers, the completed rectifiers are checked under maximum operating
conditions for forty-eight hours at 130 volts a.c., 350 ma., and 55�C. This results
in an extremely efficient rectifier that does not change its electrical characteristics
significantly with time.
Fig. 3 shows the static characteristics of an average G-10 taken at different
ambient temperatures. The rather rapid increase in inverse current at the higher
temperature tends to place an upper limit on the useful temperature range of the
Germanium Dot Rectifier. This upper limit is believed to be inherent in most semiconductor
devices, as it is thought that inverse currents are largely generated by thermal
agitation at the rectifying surface.
Fig. 4 shows the static resistance, at room temperature, for an average G-10.
It is of interest to note that the rated peak-to-peak voltage of the G-10 (400 volts)
falls on or near the point of maximum resistance of the Germanium Dot Rectifier
at room temperature.
In many circuits the efficiency of this unit is at least 98%. For example, with
a 50-watt resistive load, the power dissipated within the rectifier as heat is usually
less than 1 watt. Operation at 50°C does not materially affect this efficiency.
Other types of rectifiers may lose as much as 5% of their room temperature efficiency
Another advantage of this rectifier is the low effective capacity, usually about
20 μμfd.; making it possible to operate dry disc type power supplies from
25 cycles to about 50 kilocycles. This characteristic is of particular advantage
in lightweight installations, such as aircraft and mobile power units. Here a high
frequency alternator with a G-10 rectifier and a small filter will provide low noise
and ripple content d.c. power over wide extremes of temperature, vibration, and
The life expectancy of the Germanium Dot Rectifier is believed to be well in
excess of 10,000 hours at full load and 40°C. At the present time, several units
have been on test for more than 4000 hours at full load, at 40°C with no significant
changes in their electrical characteristics. This figure has been limited only by
a lack of time in which to take the test to completion.
Some typical characteristics for the Germanium Dot Rectifier with various filter
condensers at room temperature are shown in Figs. 5 and 6 for two types of rectifier
circuits. An average selenium rectifier is shown for comparison. It will be noted
that the slope of the curve is mainly a characteristic of the size of the condensers
used, but that the efficiency of the rectifier determines the position of the curve.
A doubler circuit has been successfully used at temperatures as high as 90°
C ambient with the characteristics as shown in Table 1.
Excessive overload in the half-wave circuit, or the voltage doubler circuit,
generally causes the rectifier to short-circuit. This usually opens a series fuse
or surge resistor and damages the rectifier irreparably. If this occurs, there is
no disagreeable odor from the G-10 as is often the case with other type rectifiers.
The recommended surge or current limiting resistance has been tentatively established
at the same values used with selenium rectifiers, i.e., approximately 5 ohms. There
is some indication, however, that this may be reduced to approximately half of this
value. Even at 5 ohms, the series condenser ripple-current ratings must be increased
to prevent condenser damage, due to the higher surge and ripple currents that result
from the lower forward resistance of the Germanium Dot Rectifier.
The Germanium Dot Rectifier is not seriously deteriorated by humidity due to
the butyl rubber sealed metal case; several test units have successfully completed
50 or more cycles of operation under maximum load conditions at 90% to 95% relative
humidity. Each cycle consists of two periods of four hours of rectifier operation
separated by an eight hour period of inactivity.
Additional research is underway to improve the accuracy of tests and to provide
a faster and more complete stabilization, together with operation at higher temperature
ambients and current ratings than are presently possible.
Fig. 3. Static characteristics .of an average G-10 taken at different ambient
temperatures ranging from 25 to 75 degrees C.
Fig. 4. Static resistance at room temperature.
Table 1. G-10 characteristics in a doubler circuit at ambient temperatures to
Table 2. Tentative electrical characteristics for the G-10 Germanium Dot Rectifier.
Fig. 5. Some typical characteristics for the G-10 in condenser-input power circuit,
Fig. 6. Performance graph of the G-10 when used in a conventional doubler circuit.
Posted October 6, 2021