US2144236A - Oscillation generation system - Google Patents

Description

Jam 17, 1939. J. N. WHITAKER soILLATIoN GENERATION SYSTEM Filed Jan. 28, 1937 2 Sheets-Sheet l INVENTOR JAMES N. WHITAKER Jan. 17, LINy wHlTAKER v 2,144,236

OSC ILLATION GENERATION Y SYSTEM Filed Jan. 28, 1937 2 Sheets-Sheet 2 INVENTOR JAM ES N. WHITAKER i BY MMM.

ATTORNEY Patented Jan. 17,' 1939 UNITED STATES OSCILLATION GENERATION SYSTEM James N. Whitaker, Tuckahoe, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 28, 1937, Serial No. 122,727

2 Claims.

This invention relates to oscillation generation systems, and particularly to a mechanically controlled oscillation generation system.

A primary object of the present invention is to provide a source of oscillations of constant frequency and constant amplitude.

Another object is to provide such a source which is particularly adaptable for use in the audio frequency range below ten thousand cycles.

A further object is to provide a system for generating oscillations of constant frequency and constant amplitude which is compact and substantially unaffected by temperature changes.

A still further object is to provide such a source of constant frequency and constant amplitude of output whichV may be operatedfrom the standard power supply systems regardless of the usual fluctuations in voltage encountered in such a system. Y

In general, the foregoing objects are achieved by the provision of a reed controlled tone source incorporating an amplitude limiting arrangement in connection with an arrangement for driving the reed. Essentially, the circuit consists of a reed assembly including a suitable reed, a driving coil for the reed, a phasing condenser for the drive coil, and a pair of pick-up coils, these pick-up coils supplying energy to the grids of a pair of amplifier tubes from one of whose outputs energy is fed back through an overloaded drive tube to the phasing condenser in series with i the reed drive coil, while from the other output energy of constant frequency and comparatively constant amplitude is derived. The level of this derived energy of constant frequency and constant amplitude is governed by a suitable adjustment of the potentiometer in the grid circuit of the second amplifier tube. A suitable power supply system employing a full wave rectifier unit and a low pass filter and a resistorcapacitor filter of conventional design serves to supply the power required to various portions of the system.

A feature of the invention resides in the particular material used for the reed for controlling the frequency of oscillation. A further feature lies in the'conguration of the reed wherein a tapered reed of relatively smallv dimensions offers a continuously varying impedance to vibration along its `length from 'the narrow tipped portion to a wider vibrationless and rigidly mounted base. i

AA further feature resides inthe use of the circuit per se, which incorporates amplitude limiting means, whereby a substantially constant value of driving power is applied to the reed element regardless of power supply variations, provided, of course, that said power supply variations are within reasonable limits.

Other objects and features of the invention Will appear from a reading of the following description, which is accompanied by drawings wherein:

Fig. 1 illustrates a complete oscillation generation system in accordance with the invention, including a power supply system, driving circuit,A and reed assembly;

l Fig. 2 illustrates an exploded view of the compact reed `assembly of the invention; and

Fig. 2a illustrates the physical configuration of one embodiment of the reed, showing the tapered construction together with its base member.

Referring toFig. 1 in more detail, there is shown a reed assembly I for controlling the frequency of an oscillation generation system comprising a twin-triode amplifier 2 from one of Whose anodes feed-back energy is supplied to a driving tube 3, and from whose other anode output energy is supplied through a suitable transformer 4 to a utilization circuit 5. A conventional type of power supply system 6, employing a suitable transformer l, a full wave rectifier 8, and a resistor-capacitor filter 9 serves to pass operating potentials to the various portions of the circuit.

Reed assembly I, which -is described later in more detail in connection with Fig. 2, includes a suitable reed I!) of tapered configuration; a drive coil II for maintaining the reed in vibration; a blocking and phasing condenser I2 which serves the purposes of isolating the drive coil II from the direct current potential applied to the anode of tube 3, providing feed-back of the proper phase to maintain the vibration of the reed member ID and, finally insuring a low power factor in the feed-back circuit; and a pair of pick-up coils I3, I3, connected together in series as shown, for supplying energy to the grids of G, GI of the amplifier 2. The poles of the pickl up coils I 3, I3, each consist of extremely thin laininated magnetic material suitably connected to the poles of a permanent magnet I4. In some instances, there may be provided in the reed assembly a tuning condenser I5 directly across the pick-up coils in shunt with the two coils I3, I3, considered in series for improving the wave form. The reed assembly in its preferred form includes a plurality of contact members in the form of plugs I6, I6, which are adapted to be inserted into a set of jacks I'I, I1, the later of which are directly connected to the main portion of the oscillation circuit.

The twin-triode tube 2 comprises, in effect, two class A ampliers for producing linear amplification of the energy impressed on the grids G and GI of the tube, in turn derived from the reed assembly I. The anode I8 of one of the amplier devices in tube 2 is connected as shown through a blocking condenser I9 to the grid 20 of the amplitude-limiter drive tube 3, while the other anode 2I of the amplifier tube 2 is connected to a suitable utilization circuit 5 through the transformer 4. A suitable potentiometer 22 in the grid circuits of the twin-triode amplifier tube is used to vary the potential applied to grid GI through its variable member 23, thus governing the level of the energy supplied to the transformer 4. VSuitable positive potentials are supplied from the power supply system 6 to the anodes I8 and 2| of the amplifier tube 2 through the resistor 21S. and primary winding 25 of the transformer 4, respectively.

The reed driving tube 3 is arranged to function as an overloaded tube whereby the output provides alternately saturated current or no current, depending upon whether a positive or negativepotential is applied to the grid 20 .from the amplifier tube 2. It will thus be seen that the tube `3'is a limiting device which provides a constant value of driving power to the drive coil II `through the condenser I2, even though Vthe alternating current input to the `grid 20 is subject to a wide variation of amplitude. This same limiting action will Ytake place for any reasonable variation in voltage of the power supply system 6 which supplies positive potential to the anode of the drive tube 3. In the arrangement shown in the drawings, the grid 20 has no applied grid bias other than that supplied by the alternating current energy from the amplifier tube.

With a circuit arrangement of the type shown in Fig. l, whose elements had the values indicated in the drawings, and with a suitable reed made of a low chromium content, stainless steel, such as is used in ordinary stainless steel vegetable knives, there was obtained oscillations of a constant frequency of 4860 cycles and of constant amplitude. At this time, it should be noted that the low vchromium content, stainless steel is suitable for use in the invention not only from the standpoint of vibration and because of its magnetic properties, but also because the material is free from corrosion. Although ordinary steel reeds may be and have been used satisfactorily, such reeds are not very suitable from a maintenance standpoint because they have been found, in time, to corrode, and thus change their frequency of vibration with a consequent change in the frequency of oscillations of the generator.

One advantage of the present invention is that the frequency of oscillations generated is substantially constant, irrespective of normal temperature and power supply fluctuations within reasonable limits. It was found that with one embodiment the frequency stability of the reed controlled tone source of the invention is, better than .02% per degree centigrade of temperature variation, within a range of from 21 to 52 centigrade, and such stability is not appreciably affected by voltage variations of to 20% in the power supply system.Y

Fig. 2 is an exploded view of the details of the reed assembly'l of Fig. l, which shows, in perspective, the various component parts thereof, the same parts in both figures being represented by the same reference numerals. The pole pieces of coils II and I3, designated in Fig. 2 by the reference character 26 and 26', respectively, consist of extremely thin laminations, each lamination being about IAOOO thick and varnished to reduce eddy current losses. Reed Il] is shown as being extremely thin in width and tapered in its longitudinal dimension, the base portion thereof being soldered or rigidly attached to a suitable mounting member 2l, said member being fastened securely through screws, designed to be inserted into holes 28, to the bottom of the drive coil reed-support 29. When the reed I0 is in position on the support 29, and said last support is mounted on housing 3U in which the pick-up coils I3, I3, and their associated elements are held, the free vibrating end of reed I0 will be adjacent to and slightly spaced away from the pole piece 26 of drive coil II on the one side, and the pole pieces 26', 26 of the pick-up coils I3, I3, on the other side, whereby movement of the reed I0 is caused by the energy applied to coil II, and such movement in turn produces variations in the iiux path between the pole pieces of coils I3, I3. When the reed Ill is thus secured in position between the pole pieces 26 and 25', 26', the end of reed I0 is free to vibrate within reasonable limits when excited by the energy applied to drive coil II, and it is these vibrations which cause fluctuations in the flux path of the coils I3, I3. An inspection of support 29 for the coil II and the reed I0 with its associated mounting 21, will show that the underside portion of the support 29 is recessed to provide ample room for the free vibration of the reed and also for providing a space within which the mounting 21 for the reed may be secured. The laminated core or pole piece 26 of the driving coil I I, together with its adjusting screws 3I, may be moved closer to or farther away from the reed I0 by the adjustment of a suitable clamp, to vary the amount of driving power effective upon the reed. The frequency of oscillation of the system is determined primarily by the length, width and thickness of the reed I8, although small frequency adjustments may be made by varying the amplitude of vibration of the reed, and this last may be accomplished by varying the distance between the reed and the driving pole piece 2S. In practice, the desired dimensions of the reed are obtained by first making the dimensions of the reed such that the frequency would be somewhat lower than the desired frequency, and then obtaining the desired frequency of oscillation of the reed by very carefully grinding off or cutting down the length of the reed until the desired frequency is secured. These dimensions of the length are observed by making frequency measurements as the grinding operation proceeds. If perchance the reed is shortened beyond the desired length, whereby a higher frequency than what is desired is obtained, then the frequency of the oscillator can be lowered by reducing the thickness of the reed. As an illustration of the dimensions which the reed may take, one reed actually used'in practice to produce audio frequency oscillations below 10,000 cycles, was made of low chromium content, stainless steel, approximately 1/3 in length from its tip to the nearest portion which is soldered to its mounting, the width of the free end being V24 while the width of that portion adjacent the base on the mounting is 3/24. 'Ihe thickness of this particular reed is approxiately 12/1ooo. These dimensions will, of course, as explained above, vary with the frequency at which it is desired to have the reed operate.

The tapering of the reed is a very important feature of the invention, inasmuch as such shaping reduces the damping action of the base of the reed (which is rigidly mounted to its support) upon the free vibrating end. In effect, the reed continuously varies in its impedance to Vibration from a rigidly clamped base to an almost perfectly free vibrating tip.

Although the invention has been described with particular attention to a low chromium content, stainless steel reed, it is not limited thereto inasmuch as reeds of other materials, such as quartz (or other crystalline substances) and ordinary steel may be used in the same circuit as that described above, the disadvantage in ordinary steel being, as stated above, in its susceptibility to corrosion. The quartz reed, however, may be electrostatically controlled in a suitable manner, or, if its surfaces are coated with metal by a suitable process, the quartz may be electromagnetically controlled in identically the same manner as the chrome-steel reed described above. In the last case, if desired, the quartz crystal may have suitable metal plates of appropriate size, let us say, for example, 1/8" in width, cemented to both sides thereof instead of to metallized surfaces.

Another modification of the quartz reed is to coat both sides of the reed with suitable conducting surfaces insulated from one another; energy may thus be derived therefrom due to normal piezo electric reaction of the crystal when under mechanical stress. In this last case, of course, as in the case of the reed of Figs. l and 2, the quartz reed will be suitably tapered.

What is claimed is:

1. A constant frequency, constant amplitude oscillation generation system comprising two sets of linear amplifier elements each having an input and an output circuit, a frequency controlling circuit connected to the input circuits of both sets of linear amplifier elements, a feed-back circuit from the output circuit of one set of amplier elements to said frequency controlling circuit, said feed-back circuit including an electron discharge device Whose grid is biased to give saturated output current upon the application of a slight positive potential to said device from said last set of amplifier elements, said device having input potentials applied to its grid from said last output circuit and having its anode coupled to said frequency determining circuit, whereby the phase of the energy in the anode circuit is reversed relative to the energy in the grid circuit, a phasing condenser in said feed-back circuit, a utilization circuit coupled to the output circuit of said other set of amplifier elements, and a potentiometer in the input circuit of said last set of amplifier elements for regulating the level of the energy supplied to said utilization circuit.

2. A constant frequency, constant amplitude oscillation generation system comprising two sets of linear amplier elements each having an input and an output circuit, a frequency controlling circuit connected to the input circuits of both sets of linear amplifier elements, a feed-back circuit from the output circuit of one set of amplier elements to said frequency controlling circuit, said feed-back circuit including an electron discharge device whose grid is biased to give saturated output current upon the application of a slight positive potential to said device from said last set of amplifier elements, said device having input potentials applied to its grid from said last output circuit and having its anode coupled to said frequency determining circuit, whereby the phase of the energy in the anode circuit is reversed relative to the energy in the grid circuit, a utilization circuit coupled to the output circuit of said other set of amplifier elements, and a potentiometer in the input circuit of said last set of amplifier elements for regulating the level of the energy supplied to said utilization circuit.

JAMES N. WHITAKER.

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