delivered the opinion of the court:
Plaintiffs seek to recover for the alleged infringement of two patents, referred to herein as the MacLaren patent and the Aceves patent, both of which relate to electronic tubes and circuits. Both of these patents, are directed to the avoidance of distortion in electronic amplification, and plaintiffs allege that both patents are infringed by the manufacture by or for and use by the United States of certain electronic circuits utilized in connection with radar systems.
The defendant contends that, in so far as the claims in issue here are involved, neither patent in suit is infringed; that neither patent discloses novelty over the prior art; that the alleged infringing circuits are essentially like those of the prior art and, hence, if any claims of the patents were construed as infringed they would be anticipated.
The essential facts established by the record in this case are fully set forth in the findings and except in certain controverted issues hereinafter discussed, it is unnecessary to refer to them in detail.
In order to present an intelligent discussion of this matter it is necessary to revert to some of the basic principles of amplification.
A conventional amplifier consists of a glass tube enclosing three elements. One of these is a heated filament termed a “cathode.” The second is a small plate. When these two *689elements are connected by an external circuit which includes a source of electrical energy of substantial voltage, such as a battery of 100 to 200 volts, with the positive pole of the battery connected to the plate and the negative to the filament or cathode, a flow of electrons takes place from the same to the plate and provides a path inside the tube for current flow from the battery between the plate and cathode and through the external circuit.
The third element in the tube is the heart and soul of this contrivance and consists of a metallic screen, termed a grid, interposed between the cathode and plate. If this screen is connected to an external circuit which makes it a few volts negative with respect to the cathode, it exercises a powerful influence upon the electron stream passing through it, and may, if sufficiently negative, even interrupt this stream entirely. Thus the grid becomes in effect the “spigot” or “gate” for controlling the amount of flow of the electron stream from the cathode to the plate or even cutting it off completely.
Starting with the “spigot” closed, i. e., sufficient negative voltage on the grid to completely block the electron stream, it may next be contemplated that it is slowly turned toward an open position, i. e., by decreasing the negative voltage. As this occurs, the intensity of the electron stream will correspondingly increase, with a consequent increase in the flow of electrical energy in the external circuit connected to the plate and filament. If we next assume that the negative voltage has been reduced to zero, the “spigot” is still not fully open. To open it completely and still further increase the electron stream we must pass through the zero point and apply an increasing positive voltage to the grid.
This brings us to an underlying and important fact in the present issue. Whenever the grid becomes positive it also attracts electrons which cause a conflicting flow of electricity back into whatever is supplying the control voltage to the grid.
For this reason it is essential in a conventional amplifier that the input voltage waves or variations, which find their origin in such devices as a microphone, phonograph pickup or photoelectric cell, operate within a relatively narrow negative range. As these voltages vary in accordance with the *690sound waves of the voice or music being reproduced, they must at no time impress upon the grid a sufficiently high negative voltage to cut off the operation of the tube nor a positive voltage which will cause the conflicting flow of electricity back into the input circuit. This is necessary in order to avoid distortion and to produce in the output circuit of • an amplifier a magnified facsimile of the input. The “spigot” or “gate” to which we have referred by way of analogy, must neither be completely closed nor opened too wide.
It was to this problem that MacLaren’s efforts were directed. He desired to increase the power output of an amplifier tube by giving the “spigot” a greater range of opening, thus providing for a greater electron flow in the tube. Mac-Laren states his purpose so succinctly that we quote at this point the second object of his invention from his patent:
provide a method and a means for compensating for the ordinary distortion produced when the grid of an amplifying tube is positive so that the grid may swing either negative or positive and still produce true amplification at the output of the tube.
MacLaren attempted a solution by employing a circuit between the signal source and the grid of his amplifier tube and which included what he calls a compensating tube. The intended purpose of this was to automatically compensate for the conflicting flow of electricity back into the input system whenever the grid of the amplifier tube became positive.
Without going into the details of this circuit and its operation, which are already set out in. findings 9-14, inclusive, we refer to one important feature. The cathode of the compensating tube is directly connected to the grid of the amplifying tube by means of a continuous metallic wire which MacLaren refers to as “a circuit of substantially zero impedance,” which, in plain, every day terms, as well as in technical parlance, means that there is substantially nothing to impede current flow in this circuit. It is by means of this circuit that the electrical energy, which causes the electron flow in the compensating tube, is supplied from the grid of the amplifying tube.
It was here that MacLaren stumbled. While he developed a system in which compensation for distortion took place *691whenever the grid of the amplifier was operated in the positive region, his system would not function with the grid operating in both the negative and the positive regions which he indicated as the object of his invention. When the grid in the amplifying tube becomes negative it no longer receives electrons from the cathode, and there is then no source of electrical energy for energizing his compensating tube. In using the MacLaren circuit it is therefore always necessary to keep the grid of the amplifying tube at all times positive. Still referring to our analogy of the “spigot,” it must at all times be rather fully opened whether the input circuit is quiescent or is receiving a series of sound-produced impulses to be amplified. This results in a relatively heavy continuous flow of electrons and current in the amplifying tube, which tends to overheat the tube.
Aceves then stepped into the picture. Seeing these defects in MacLaren’s circuit, he attempted to remedy them. Findings 16 to 21 detail what changes Aceves suggested in the MacLaren circuit, and which became the subject-matter of his patent. Aceves’ thought was to connect to a common point of the entire system or to “ground” MacLaren’s circuit extending between the cathode of the compensating tube and the grid of the amplifying tube through a device known in electrical parlance as a “filter.” This filter consists of a coil possessing large inductance but of extremely low ohmic resistance. The operation of this device has been covered in detail in the findings and it is sufficient to state here that such device will provide a ready path to ground for direct current flow while rejecting the varying voltage waves which find their origin in the sound waves at the input of the system. This device thus forces the varying electrical energy due to the sound waves to pass from the cathode of the compensating tube through the direct connection to the grid of the amplifying tube and at the same time permits the grid of ■the amplifying tube to assume an approximate zero voltage with respect to its cathode which is also grounded.
Aceves by permitting the grid of his amplifier tube to operate at or near zero potential enables the varying voltage .impulses coming into it to swing both in the positive and negative regions, thus correcting MacLaren’s mistake and *692at the same time limiting the detrimental effects of a relatively heavy normal current flow in his amplifying tube.
Aceves makes a suggestion in his specification that a source of steady potential could be inserted between his inductance coil and the ground. To do this would vitiate the objects sought by Aceves. This matter is discussed in detail in Finding 21, to which plaintiffs have taken exception. There is ample foundation in the testimony for this finding. .
Aceves also suggests that a resistance may be used in shunt or series with his inductance or filter coil. This does not teach nor suggest that an ohmic resistance may be used instead of the filter coil. To do so would do away with any filter effect and would make the grid of the amplifying tube positive, which would be directly contrary to the use of the vanishingly small resistance which Aceves suggested in order to correct MacLaren’s mistake and to limit the normal flow of current in the amplifier tube.
Summarizing both the MacLaren and Aceves patents, they are both directed to avoidance of distortion in an amplifying system. They both employ a direct connection between the cathode of a compensating tube and the grid of an amplifying tube to control the electron flow in the latter. Aceves adds to this contribution the teaching that the grid of an amplifying tube may be operated at or near a normal zero potential and that normal current flow may be limited in the amplifying tube by means of a filter of extremely low ohmic resistance inserted between the direct connecting wire and the ground to which the cathode of the amplifying tube is also directly connected.
The defendant’s structures alleged to infringe are radar sets. Their operation is described in Findings 26 to 31, inclusive. It is necessary only to state here that they operate on the principle of receiving the echo of a directed radio-wave like a searchlight beam which is sent out into space by a, powerful transmitter, and which when it hits an object such as an airplane, bounces back and is picked up by a receiver-adjacent the transmitter. The duration of time between the radio wave sent out by the transmitter and its arrival at the receiver is measured by electronic devices, and this time interval gives the distance to the target.
*693The portion of the radar system alleged to infringe and with which we are concerned, is a pulse-forming device or electronic switch which turns on the transmitter for a minute interval of time approximating one-millionth of a second and then shuts it off while waiting 586 millionths of a second for an echo to come back. This operation is repeated periodically at the rate of 1,707 times per second.
This device consists of an electronic tube in which two grids are located between the cathode and the plate. (While the tube has three grids, we are here only concerned with the operation of two of them.) Each of these grids normally has a sufficient negative voltage applied thereto to entirely prevent any electron stream from flowing between the cathode and the plate, and thereby flow of electrical energy in the plate and output circuit of the tube is prevented.
Referring to our previous analogy of a “spigot” or “gate,” both “spigots” are completely shut and as they are both located between the cathode and plate the opening of either one alone will not permit an electron stream to flow. Both gates or “spigots” must be opened before the electrons can flow.
Both grids are supplied with periodic waves or pulses which cause them to change their voltage from negative to positive, thus periodically opening the “spigots” or “gates” from a completely closed to a wide open position. These pulses are different both in periodicity and character and find their origin in a device which for our present purposes is sufficient to call a master electronic clock. This is all discussed in detail in Findings 29 and 30, the pulse shapes being illustrated in Finding 30. It is solely necessary to emphasize here that only at certain intervals do the incoming pulses coincide and only then do the grids permit the flow of energy. When this happens the pulse occurring in the output of this tube is different in shape and character from either of the incoming pulses. It is this pulse that energizes the transmitter.
A comparison of the accused structure with the patents in suit is next in order. The upper grid in the defendant’s pulse-forming tube receives its controlling pulses from a circuit connected to the cathode of a preceding tube, which *694in turn is periodically operated by the master electronic clock. This is for the purpose of applying a strong burst of positive potential at the appropriate time. As far as feeding the grid of a succeeding tube from the cathode of a preceding tube is concerned, the Government structure and the patents in suit are similar. Here, however, similarity ceases.
Both patents in suit utilize a direct connection for this purpose. Instead of using a direct connection or a path of zero impedance the Government structure interrupts this circuit between the cathode of the first tube and the grid of the second tube by inserting therein what is known as a blocking condenser. This is a device which will permit the periodic pulses of relatively high frequency to flow from the cathode of the preceding tube to the grid of the second tube although at the frequency involved it presents an impedance of 9,350 ohms. It will also block the flow of any direct current in this circuit by offering infinite impedance thereto. It is by virtue of this blocking condenser that it is possible to isolate and to normally apply to this grid of the pulse-forming tube a normal negative voltage of 20 volts, thus keeping the “spigot” tightly closed until a positive pulse comes through. The Government device would become inoperative were this circuit not interrupted by the blocking condenser.
We next take up the claims in suit. It is too well settled in patent cases to require citation, that the terminology of the claims of a patent must be interpreted in the light of the disclosure of the specification by what structures are therein described and how they function. Claim 14 of the MacLaren patent, the only claim of that patent in suit, specifies the circuit that we have just discussed as “a connection of substantially zero impedance.” Such a circuit is not present in the Government structure.
Claim 14 of the MacLaren patent also includes as an element “an amplifying triode.” We do not think that the pulse-forming tube of the Government structure amplifies in the sense that it is used in either of the patents in suit or by those skilled in the art. It is not intended to produce in its output circuit an enlarged facsimile of the signal introduced into the input of the tube. Instead, it is a switch *695operated at the proper times by the combined pulses sent to its grids by the master clock to turn on and off the transmitter of the radar set.
As set out in Findings 38 and 39, claim 14 is not infringed.
Claims 6, 22, 23, and 27 of the Aceves patent are in suit. These claims all specify in slightly varying phraseology the “direct connection” between the cathode of a first tube and the grid of a second tube, the circuit that we have discussed supra. As already explained, the defendant’s device does not have this circuit and these claims are not infringed.
Other limitations occur in this group of Aceves’ claims which point to noninfringement. These deal with the limitation of the normal flow of the plate-cathode current in the second tube of Aceves’. For this he basically depends upon his inductive filter of “vanishingly small resistance” providing a direct current path from grid to cathode of his second tube.
In the Government device this normal current is not only limited' but reduced to zero by the high negative voltage applied to the grid by virtue of the blocking condenser, an entirely different structure.
These distinctions are set out in Findings 41-44, inclusive, and except to state we think these findings are supported by the record, it is unnecessary to reiterate them here.
The two prior art patents pertinent to the question of validity are referred to in detail in Findings 38 to 37. These are the Massolle and the Nakken patents. The Massolle patent states that it “relates to improvements in the arrangement of circuits for electric amplifiers,” and the patent to Nakken states that the object “is to improve amplification of feeble energy manifestations through the medium of the thermionic triode amplifiers.”
Not only are Massolle and Nakken directed to a solution of the same basic problem that MacLaren and Aceves attempted to solve but they did it in the same way. In each of these prior art disclosures the circuits shown and described teach the feeding of a signal input to the grid of an amplifying tube from the cathode of a preceding tube by means of a direct connected metallic circuit. The Nakken patent, in addition, both describes and shows the grounding or connec*696tion of this circuit and its return to the cathode of the amplifying tube by means of a coil having high impedance and relatively low ohmic resistance, a device which is similar to what we have previously referred to as the Aceves filter and by means of which he attempted to cure the difficulties present in the MacLaren patent.
Both of these prior disclosures show a photoelectric cell as an input device and telephones connected to the output of the amplifying tube.
Plaintiffs raise several curious contentions with' respect to the disclosures of these patents. One of these is that the problems of MacLaren and Aceves do not arise in the amplification of the output of photoelectric cells because of their rather weak pickup characteristics. We see no merit to this. This, even if true, would only result in a weaker amplified signal which is a matter only of degree. The function of the circuits is the same. In addition, neither of the patents in suit is limited to the use of any particular type of input device and the monopoly expressed by the claims in suit would not exclude the use of signals originating in a photoelectric cell.
Plaintiffs also urge that if the circuit of the Massolle patent here relied upon has any bearing on MacLaren and Aceves, it is only because of an accidental disclosure. The Massolle circuit is no more accidental than the disclosures of MacLaren and Aceves. These are all patents directed to the improved amplification of electrical signals. One skilled in the art at the time of the Massolle disclosure could clearly reproduce the Massolle circuit from the disclosure. While it is true that Massolle did not completely explain how his circuits operated, he did not have to do so. In fact, when MacLaren attempted to explain the operation of his circuit he made a mistake which Aceves later corrected. The prior art circuits and their operation with the direct connection between cathode and a subsequent grid are more analogous to the circuits of the patents in suit than is. the circuit of the Government device.
As indicated in Findings 40, 45, and 46, claim 14 of Mac-Laren and claims 6, 22, 23, and 27 of Aceves are invalid in view of the prior art.
*697Plaintiffs further urge that a presumption of patentability should be based on the fact that numerous licenses have been issued in connection with the patents in suit and this points to commercial success. It is true that when invention is in ■doubt, acceptance of the same may be thrown in the scale, but this is only when one must weigh carefully the teachings ■of the prior art as compared with the claims in issue. In the present instance we think that the teachings of the prior .art are clear and we are in agreement with In re Thayer, 143 F. (2d) 996, 1000, in which it is aptly stated—
* * * However, commercial success is only one element to be considered in determining the patentability of claims, and when, as in the instant case, the prior art either discloses or plainly suggests the structure and the process defined by an applicant’s claims, commercial success is not of great importance.
Moreover, none of these licenses was limited to the patents fin suit and none granted a license under less than seven patents. Acceptance and usage of an article depend upon jnany factors, and in the present instance we do not feel that ■these licenses materially affect the issue of patentability.
For these reasons, we are of the opinion that claim 14 of MacLaren and claims 6, 22, 23, and 27 of Aceves are not infringed and are invalid.
The petitions are accordingly dismissed.
It is so ordered.
Howell, Judge; MaddeN, Judge; Whitaker, Judge; and XittletoN, Judge, concur.