US2054899A - Oscillator system - Google Patents

Description

Sept. 22, 1936. w. w. E lTEL ET AL.

05 C ILLATOR S YSTE M Filed Feb. 27, 1934 ELL J INVENTORS, WILL/Ann. E/TEL.

JACK McCUL'LOUGl-l.

Patented Sept. 22, 1936 UNITED STATES PATENT OFFICE 0 SCILLATOR SYSTEM William W.

Ltd., San Francisco, Nevada Eitel and Jack Bruno, Calif., assignors to Heintz McCullough, San & Kaufman, Calif., a corporation of Application February 27, 1934, Serial No. 713,106 2 Claimsa (01. 250-47) current of an oscillating tube may be used to stabilize the heat dissipation of an oscillating tube when keyed; and to provide a vacuum tube oscillator and circuit of remarkable stability at high frequencies.

Other objects of our invention will be apparent or will bespecifically pointed out in the description forming a part of not limit ourselves to the embodiment of the invention herein described, as'various forms may be adopted within the scope of the claims.

The figure is a diagrammatic representation,

reduced to lowest terms, of a vacuum tube oscillator and associated circuits, showing a preferred connection for keying, and heat dissipation control.

It is well known in the art that stability of output of a vacuum tubeoscillator is dependent upon arelatively large number of factors. One of these factors is the heat dissipation of the tube itself. In other words, the output frequency changes in an oscillator as the temperature of the tube changes, and in many oscillators which are keyed, that is, which are started into oscillation and stopped by the use of some keying means, the heat dissipation during the period of oscillation is entirely different in amount from that occurring when the tube is not oscillating. There is, consequently, a change in frequency occurring immediately after the key is depressed, giving rise tothe familiar chirping which is often heard in a heterodyne receiver. Such a change in frequency, while not fatal in the medium high frequencies, may be sufficient in the extreme high frequencies to ruin the operation of the system as a transmitter.

Our invention, broadly, as to method, comprises allowing a vacuum tube to oscillate, thereby producing grid current. We then utilize this grid current to operate a relay so that when the tube stops oscillating and no grid current is taken, the relay is operated to change the grid bias to a value which will permit the tube to dissipate substantially the same amount of heat as it did when this specification, but we do it oscillated. The tube, under these conditions, will not change its temperature appreciably during keying, and the frequency, at least as-far-as this particular factor is concerned, will tend to become stabilized. v

As to apparatus, we prefer to use the tube connected in the familiar tuned-plate tuned-grid circuit which, as is well known, provides of itself a relatively stable oscillator, and then to pass grid current drawn by the tube through a relay device to decrease the bias on the tube when the tube is not oscillating.

Our invention may be better understoodby reference to the figure which illustrates a three electrode tube connected in a preferred tunedplatetuned-grid circuit embodying our invention. It should be here noted that the keying means and method shown is the subject of our application, Serial No. 713,107 filed February 2'7, 1934,

now Patent No. 2,026,874, granted January '7,

A vacuum tube 5 having the conventional cath-v ode 2, grid 3, and anode 4, is connected in'a tuned-plate tuned-grid circuit comprising a grid A oscillating circuit consisting of a grid inductance i tend a'parallel grid tuning-condenser 6. 'One end of this tuned circuit is connected directlyto the grid, the other end is connected through a by-pass condenser I to a leg- 8 of the cathode 2. We prefer to ground the end of the inductance 5, through a condenser i3 and a lead 9. The tuned-plate circuit comprises a plate inductance it shunted by a plate tuning condenser?! l..- .One end of this inductance is connected to the plate and the other end is connected by a lead l2 through a neutralizing condenser M to the grid 3. A center tap i5 is provided for the plate inductance, and the positive plate supply lead I6 is connected thereto. The radio frequency is by-passed to ground through the anode condenser l'l. A convenient output coil 18 is coupled to the plate inductance ID. A negative an ode supply lead I9 is directly grounded through the negative ground lead it, and a suitable cathode bias resistor Z! is inserted between the negative anode lead i9 and the cathode lead 8. A grid bias resistor 22 is connected in series with the negative anode supply lead grounded end of the grid inductance 5 through a relay coil 23. A relay armature 24 is positioned to connect a pair of are connected to the opposite ends of ode'bias resistor 2|.

Practically all tuned-plate tuned-grid oscillators, when the tuned-grid circuit is set at the the oath- I9, and the the short across the cathode same frequency as the tuned-plate circuit, will oscillate by virtue of the grid-to-plate capacity inside the tube. Our circuit, under the same conditions, will oscillate, but we prefer to stop it from oscillating by adjustment of the neutralizing condenser M. We then prefer to utilize a series keying circuit comprising a plate keying inductance 26, coupled to the plate inductance I6, and a grid keying inductance 2'! coumm to the grid inductance 5. Both of these couplings may be fairly loose. A key 28 is inserted in one of the leads between the two inductances 26 and 27. The circuit is adjusted so that when the key 28 is closed the tube will oscillate, the positive feed-back through inductances 26 and 21 overcoming the negative feedback introduced by the neutralizing condenser M. The use of the key 28 to make and break the feed-back current starts and stops oscillation of the tube.

In practically all oscillating circuits a high grid bias is used, because the grid goes positive during a portion of the cycle, causing a grid current to be drawn. A high bias is used in order that this grid current may not become excessive. It therefore follows that when the tube is not oscillated the excessively high bias reduces plate current to a point where the heat dissipated by the tube is small, smaller than the amount dissipated while the tube is oscillating. In consequence the tube cools rapidly when it is not oscillated, and mustheat up again immediately the tube starts to oscillate.

In the circuit we have described, the ,grid has a constant bias thereon through the resister 22, but the cathode may be also biased by the resistor 2| so that the effective biasof the grid, with respect to the cathode, is a function of the sum of the biases given by the grid bias resistor 22 and the cathode bias resistor 2!. The relay armature 24 is so set that when the tube is not oscillating and there is no grid current flowing in the relay coil 23, the contacts 2525 are closed, thus shorting resistor 2| and placing a reduced eiTective bias on the grid when the key 28 is u When the key 28 is depressed the tube starts to oscillate and take grid current, this grid current flowing through relay coil 23 pulls up the armature 24 and opens bias resistor 2i, grid bias resistor resistor 2| to be and the cathode the tube a relaallowing the full bias of the 22 plus that of cathode bias impressed between the grid 3 2. Thus there is placed upon tively high bias while the tube is oscillating, but the bias is reduced when the tube is not oscil lating, allowing the nonoscillating plate current to be considerably higher than it would be if the bias had not been changed. We prefer to adjust the relative biases given by the resistors 25 and 22 so that the heat dissipation of the tube l during oscillation is relatively constant, thm eliminating from the circuit one of the factors which tends toward inconstancy of oscillating output. 7

In the circuit as shown we also prefer to make the inductance ill relatively high and the condenser ll small, and contrariwise, make the grid inductance 5 relatively small and the grid tuning condenser 6 large. This again tends to stabilize the normally stable tuned-plate tuned-grid circuit.

It is obvious that other means may be used to accomplish the method described, as there are biasing devices other than resistors in use in the art and other Ways of connecting a relay or similar device to change the bias so that the heat dissipation within the tube will be constant, thereby tending to stabilize oscillations.

We claim:

1. In combination with a thermionic tube, and associated circuits adapted to set said tube into and out of oscillation under control or" a keying device while maintaining all electrodes of said tube energized, means for biasing the grid of said tube at a potential whereat sustained oscillation causes the generation of grid currents, and means under the control of said grid current for decreasing the amount of said bias when said tube is not oscillating to maintain substantially uniform heat dissipation from said tube during keying.

2. In combination with a thermionic tube and associated circuits adapted to set said tube into and out of oscillation under the control of a keying device while maintaining all electrodes of said tube energized, means for biasing the grid of said tube at a potential whereat sustained oscillation causes the generation'of grid current and means under the control of said grid current for decreasing the amount of saidbias when said tube is not oscillating to the point where the heat dissipated by the tube in non-oscillating condition is substantially the same. as when osciliating.

WILLIAM W. EITEL. JACK MCCULLOUGH.

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