US2014913A - Circuit for precision control of master oscillators - Google Patents

Description

A. H. TAYLOR Filed Feb. 8, 1935 Sept. 17, 1935.

I CIRCUIT FOR PRECISION CONTROL OF MASTER OSCILLATORS w Q. E W M Q w Q 2 m L R =\/S.. m A \n m QM. u W vow Qw. vw \mw m wbw fix w ./N\ QR QN m If QM, EN! w 3 m .QU m 3V Patented Sept. 17, 1935 UNITED STATES PATNT OFFICE CIRCUIT FOR PRECISION CONTROL OF MASTER OSCILLATORS tion of Delaware Application February 8, 1933, Serial No. 655,829

4 Claims.

My invention relates broadly to high frequency oscillation systems and more particularly toa circuit for the precision control of master oscillators in a high frequency oscillation system.

One of the objects of my invention is to provide a simplified circuit for a high frequency oscillation system which is constructed to deliver oscillations of high frequency and efficiency.

Another object of my invention is to provide a circuit arrangement for a high frequency oscillator and amplifier system having a high degree of freedom from variation in frequency brought about by variations which may occur in plate voltages in the high frequency oscillation system.

Still another object of my invention is to providea high frequency oscillator and power amplifier circuit arrangement having relative simplicity of adjustment by means of direct current meters in the plate and screen circuit of the high frequency oscillation system. 7

A further object of my invention is to provide a circuit arrangement for utilizing the electrical coupling between the plate and screen electrode in an electron coupled oscillator.

A further object of my invention is to provide an arrangement of coupling system between an oscillator and a power amplifier in which the power amplifier has its input system selectively connected either to the plate electrode of a tetrode oscillator or to the screen grid electrode of the tetrode oscillator for securing maximum efficiency in the transfer of energy from the oscillator to the power amplifier while maintaining the frequency of the transferred energy, constant.

Other and further objects .of my invention reside in the improved circuit arrangement for the precision control of master oscillators as will be set forth more fully in the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates the circuit arrangement of my invention.

I have found the high frequency oscillator and power amplifier system of my invention very practical and stable in its operation. The system has a high degree of ease of adjustment and has a high output efficiency. The. high frequency oscillator and power amplifier stages are constituted by tetrodes. The grid of the power amplifier may be excited either by a connection through a. stopping condenser to the shield electrode of the tetrode oscillator or by a connection to the plate of the tetrode oscillator. A potentiometer connected across a source of high potential is provided with taps, one of the taps leading to the screen grid electrode of the tetrode oscillator and another of the taps at higher potential leading to the plate electrode. A high frequency inductance system is connected in circuit between the control grid and the anode. A pair of balancing condensers is connected in series across the inductance and a connection taken from a midpoint between the condensers to a return circuit leading to the cathode. Provision is made for connecting a balance condenser between the screen 10 grid and any point in the coil system. Depend ing on the internal constants of the particular type of tube used, this point may be either above or below the neutral potential point on the coil system. The purpose of the balance condenser is to neutralize the electrical coupling between the anode and screen grid. One end of the coil system is connected to the control grid and the other end through a stopping condenser to the anode. These ends are opposite in potential. By adjusting with the balance condenser the radio frequency potential of the screen grid, the best freedom from reactions, due to tuning of the amplifier circuit may be obtained. This reaction may be reduced to a frequency change of only one or 2 two parts in 100,000sometimes better.

The next important feature in the circuit is the fact that it is so readily adjusted to guard against variations in the oscillator frequency when the supply voltage is altered. Radio fre- 3O quency ammeters, not shown in the drawing are ordinarily of course placed in series with the anode and screen grid to determine the current which each one draws, and it has been found that when the direct current potentials of anode and screen grid are so adjusted with respect to each other that the ratio of screen grid current to anode current is about in the ratio of four to five, the circuit is remarkably free from variations due to anode voltage alterations. The changes of frequency due to anode voltage. variation of 50% are not more than one or two parts in 100,000.

Referring to the drawing in more detail, the tetrode oscillator is indicated by reference character I, having cathode la, control grid lb, screen grid lo and anode Id. The input circuit of the tetrode oscillator is completed between control grid lb and cathode in through radio frequency choke coil 2 and resistance 3. The cathode la, is energized from any suitable source of potential as represented generally at 4. The potential for the screen grid lo and anode Id is obtained from the potential source indicated at 5, which is electrically connected to the potentiometer 6. A tap l of selected potential on potentiometer 6 connects through radio frequency choke coil 8 to the screen grid electrode lc. A tap 9 of higher selected potential on potentiometer 6 connects through radio frequency choke coil ii! to the anode Id. The high frequency inductance system which is connected with the tetrode l is shown at l l. The high frequency inductance system has its terminal bridged by condensers l2 and I4 electrically connected in series. The midpoint l5 between condensers l2 and I4 is connected by lead IE to the midtap connection I! of the cathode potential supply transformer l8 leading to the power amplifier tetrode 26. The lead l9 which connects to lead It: and midtap H also provides a return path to the cathode la of the tetrode l. The inductance system H has the end lla thereof connected through lead 2| to control grid lb. The end llb of high frequency inductance l l is connected through stopping condenser 22 to the anode Id. A balancing condenser 23 is connected between the screen grid lo and a selected potential point 24 on the inductance ll intermediate the ends I la and l lb. The point 24 may be either above or below the neutral potential point on the coil system depending upon the internal constants of the particular type of tube used. The balance when adjusted, neutralizes the electrical coupling between the anode Id and the screen grid lc.

The power amplifier constituted by tetrode 20 includes cathode 20a, control grid 2%, screen grid 20c and anode 20d. The cathode 29a, is energized as heretofore stated through transformer l8. Bypass condensers 25 and 26 are connected across the two parts of the secondary winding of transformer l8. The midtap ll of transformer l8 provides a return path for the anode circuit of the power amplifier 29 through lead l9. Source of potential 5 which supplies anode voltage to the oscillator tetrode I also supplies anode voltage to power amplifier 2D. The anode circuit of power amplifier 28 includes the resonant circuit 21 constituted by inductance 28 and variable capacity 29. Bypass condenser 30 is provided across the source of potential 5 as shown. Potential to the screen grid electrode 290 is supplied from source of potential 5 through resistor 3| connected as shown. A bypass condenser 32 is provided across the screen grid 20c and the cathode 20a as shown. The potential of control grid 29b is controlled from source of potential 33 through the reactance 34 connected with control grid 20b as shown.

In order to simplify the disclosure of my invention, I have shown batteries for supplying the cathode, negative C, and the anode potentials for the oscillator and power amplifier tubes, but it will be understood that I may employ a power line circuit or motor generator sets for supplying the required operating potential.

A condenser 35 is connected between the control grid 20b of power amplifier tube 28 and the switching device 36. The switching device 38 is movable to either of two contacts represented at 31 and 38. Contact 31 is connected through lead 39 to screen grid lc of the tetrode l Contact 38 is connected through lead 40 to the anode Id of the tetrode l. Under different conditions greater stability of operation may be obtained by providing the alternative connection which I have shown.

I have found that tuning of the resonant circuit 21 in the output of the power amplifier system does not impair the stability of the oscillator system when connected in accordance with my invention. The oscillator and power amplifier system of my invention have relatively great freedom from frequency changes, often brought about by variations in anode potentials. The circuits allow relative simplicity of adjustment by means of direct current meters disposed in the anode and screen grid circuit. The oscillator and power amplifier circuit is so arranged that the full realization of the benefits which accrue from the proper adjustment of the potentials on the electrodes of the oscillator and power amplifier tubes is obtained to insure minimum variations in frequency with voltage variation. The natural order of potentials on the screen grid and anode electrodes of the oscillator and power amplifier tubes is such that the condition for high energy and high stability is made to coincide.

While I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that I intend no limitations upon my invention other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A high frequency oscillator and power amplifier system comprising a tetrode including a cathode, a control grid, a screen grid and an anode, a high frequency circuit connected between said control grid and said cathode, a high frequency inductance having one end thereof connected with said control grid and the other end thereof connected with said anode, a balancing condenser, a tap on said high frequency inductance, a circuit extending from said tap through said balancing condenser to said screen grid, means for supplying relatively different potentials to said screen grid and said anode, a pair of condensers disposed in series and connected across said inductance, a tap extending from a central point between said condensers to said cathode, a tetrode constituting a power amplifier, and means connecting the input of said last mentioned tetrode with selected electrodes of the aforementioned tetrode for transferring high frequency oscillations to said second mentioned tetrode.

2. A high frequency oscillator and power amplifier system comprising a tetrode including a cathode, a control grid, a screen grid and an anode, a high frequency circuit connected between said control grid and said cathode, a high frequency inductance having one end thereof connected with said control grid and the other end thereof connected with said anode, a balancing condenser, a tap on said high frequency inductance, a circuit extending from said tap through said balancing condenser to said screen grid, means for supplying relatively different potentials to said screen grid and said anode, a pair of condensers disposed in series and connected across said inductance, a tap extending from a central point between said condensers to said cathode, a tetrode constituting a power amplifier, and means for selectively connecting the input circuit of said second mentioned tetrode across the cathode and either said screen grid or said anode of said first mentioned tetrode for effecting the transfer of oscillations to said second mentioned tetrode.

3. A high frequency oscillator and power amplifier system comprising a tetrode including a cathode, a control grid, a screen grid and an anode, a high frequency circuit connected between said control grid and said cathode, a high frequency inductance having one end thereof connected with said control grid and the other end thereof connected with said anode, a balancing condenser, a tap on said high frequency inductance, a circuit extending from said tap through said balancing condenser to said screen grid, means for supplying relatively different potentials to said screen grid and said anode, a pair of condensers disposed in series and connected across said inductance, a tap extending from a central point between said condensers to said cathode, a tetrode constituting a power amplifier, a switching device having a movable arm connected with the input circuit of said second mentioned tetrode, contacts individual to the anode and screen grid electrode of said first mentioned tetrode, said movable arm being selectively connectible with either of said contacts for effecting the transfer of energy from said oscillator to said power amplifier.

4. In a high frequency oscillator system, a tetrode including a cathode, a control grid, a screen between said control grid and said cathode, a high frequency inductance having one end connected to said control grid and the other end connected to said anode, means for supplying relatively different potentials to said screen grid and said anode, an adjustable tap on said high frequency inductance, a balancing condenser, a series circuit leading from said adjustable tap through said balancing condenser and to said screen grid, a pair of adjustable condensers connected in series and connected across the ends of said high frequency inductance, and a return path to said cathode connected between said variable condensers.

ALBERT H. TAYLOR.

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