US2651685A

US2651685A - Balanced circuit for radio apparatus

Info

Publication number: US2651685A
Application number: US38696A
Authority: US
Inventors: Nelson B Tharp
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1948-07-14
Filing date: 1948-07-14
Publication date: 1953-09-08
Anticipated expiration: 1970-09-08

Description

p 8,1953 N. B. THARP' 2,651,685

BALANCED CIRCUIT FOR RADIO APPARATUS Filed July 14, 1948 1.? .10 J1 15 12 Load I L Inductance- .Dgbw 21 22 51516 p d 1 Vail-a a no e 20 5446/ 1 17 18 1 012"; e

500x25 g. g Sup/1 y L Jource Load 51 .[nduczance Bias 51;;0! I It 0- age $055; p/ y Source Source *3 WITNESSES; INVENTOR Nelson 5. Tkaqb.

Patented Sept. 8, 1953 BALANCED CIRCUIT FOR IRA-D10 APPARATUS- Nelson B. Tha'rmElli'cott City;

Md, assign or" to Westinghouse Electric Corporation, East Pittsblifgfi, Pit a Coil 501 3115011 f PeifllS'Yl-vfiliifl;

Application July 14, 1948, Serial No. 38,696

i This invention relates to vacuum tube circuits,

and" itrelates more particularly to circuits for automatically equalizing the grid'and anode cur-- rentsot vacuum tubes working into a common load.

' In order to increase the power handling capacity of vacuum tubes,- it is common practice to connect them in parallel, push-pull, or push pull parallel, in order that two or more" tubes can work into a common load; When tubes are so connected, differences in their characteristics or in the'characteristicsot their circuit components may cause one tube to draw" morefano'de current than another tube. Likewise, when the tubes are-so operated as to draw grid current, one tubemay draw more grid current than another tube.

This invention provides a balancing circuit which will automatically balance" the grid cur-- rents and the anode currents of vacuum tubes working into a common load.

An object of the invention is'to' b'alanc'e'au'to matically the anode currents of vacuum tubes working'into a common load.

Anotherobject of the invention is to balance automatically the grid currents of'vacuumtubes working into a common load. I I

The invention will now be described with reference to the drawing of which:

Fig. 1 is a circuit schematic illustrating one embodiment of the invention as used with paral lel-connected vacuum tubes, and

Fig. 2 is a-circuit schematic illustratinganother embodiment of the invention as used'with pushpull-connected vacuum tubes. I

Referring first to Fig. l, the tubes I0, II- and I2 have their anodes connected together and to one end ofthe load inductance I3, the other end of which is connected to the positive terminal of the anode voltage supply source I4, the negative terminal of which is grounded. The grids of the tubes are connected together and through the coupling condenser I5- to'an input circuit.

The cathode of the tube I0- is connected to ground through the cathode bias resistor I6=; the'cathode of the tube I I is connected to ground through the cathode bias resistor I1, and the cathode of the tube I2 is connected to ground through the cathode bias resistor l8.

The resistor I9 is connected to the cathode of the tube I0 and to the positive terminal of the bias voltage supply source 20, the negative terminal of which is connected through the grid resistor 2| to the grids of the tubes II], II, and I2. The cathode of the tube II is connected 6 oiaim's.- (01. 179 171) through the resistor 22 to the positive terminal" of the source 20, and the cathode of the tube I2 is connected through the resistor 23 to the positive terminal ofthe source 20.

The values of the resistors I6, I 1, and I 8 should be less than the values of the resistors I9, 22, and 23', so that the normal flow of the cathode currents is through the resistors I6, I1, and I8. In the operation of the embodiment of the invention illustrated by Fig. 1, if the tubes are operated so as to draw grid current, then if the grid current'o'f the tube I0 increases, this will cause an increased voltage drop through the resistor I9 which will cause the grid of the tube to be biasedmorenegatively with respect to its cathode, thus decreasing the grid current. Likewise, if the grid currents of the tubes II and I2 increase, the increased voltage drops through the

resistors

22 and 23 will cause the grids of the tubes I I and I 2' tobe biased more negatively with respect to their cathodes, thus causing them to draw less grid current.

Regardless of whether or not the tubes draw grid current, if the anode current of the tube I0 increases without a corresponding increase in the anode currents ofthe tubes and I2, the voltage drop across the resistor I6 will increase, causing the cathode of the tube It to become more positive than the cathode of the tubes II' and I2, with the result that there will be'a current flow between the cathodes through the resistors I9; 22, and 23. The resulting voltage drop through these resistors adds to the negative bias on the grid of the tube I0, and subtracts from the negative bias on the grids of the tubes II and I2. This will result in the tube I0 drawing less anode current, andin the tubes II and I2 drawing more anode current, thus balancing the load" on the tubes. Likewise, if the anode current of either of the tubes I I' or I2 increases without a corresponding increase in the anode current of the other tubes, the cathode of. the tube with the increased current flow will become more positive, resulting in the flow of current between it and the cathodes of the other tubes;resulting in the tube drawing the greatest anode current having its grid biased more negatively, and resulting in the grids of the other tubes being biased more positively, with the result that the loads on the tubes are balanced.

In the embodiment of the invention illustrated by Fig. 2, the tubes 29 and 30 are connected in push-pull with their anodes connected to the opposite ends of the load inductance 3|, the center point of which is connected to the positive terminal of the anode voltage supply source 32, the negative terminal of which is grounded.

The cathode of the tube 29 is connected through the cathode resistor 33 to ground. The cathode of the tube 30 is connected through the cathode bias resistor 34 to ground. The resistors 25 and 26 are connected in series and. to the cathodes of the tubes 29 and 30, and their midpoint connection is connected through the re-.

sister 21 to the positive terminal of the bias voltage supply source 28. The

grid resistors

39 and 40 are connected in series and to the grids of the tubes 29 and 30, and their mid-point connection is connected to the negative terminal of the source 28.

The input signal is applied through. the coupling condensers 4| and 42 to the grids, of the tubes 29 and 3B.

The values of the resistors 33 and 34 should be less than the values of the

resistors

25 and 25, so that. the. normal. how of. the cathode current. isthrough theresistors 33 and 34.

In the operation of the embodiment of the in.- vention illustrated. by Fig. 2-, ii the tubes are operated to draw grid current, and if the tube 29 draws more. grid current than the tube.- 33, the. increased voltage. drop through the resistor 25 will cause the grid of the tube 29. to be biased more negatively with respect to its cathode, thus decreasing the grid current. grid current of. the tube 3D increases, the increased voltage drop through the resistor 2% will cause. the grid of. the tube 381 to be biased more negatively with respect. to its. cathode, thus. decreasing the flow of. gridcurrent.

Regardless. of whether or not the tubes 28 and 3B draw grid current, if the anode current. of the tube 2Q increases without av corresponding increase. in the anode current of the tube 3!), the voltage drop. across the resistor 33 will increase, causing the cathode of. the tube 29- to become more positive than the cathode of. the tube 33, with the. result that there will be. a flow of current. through the

resistors

25 and 23. The resulting voltage drops through these resistors add to the negative bias to the grid of the tube 29 and subtract from the. negative bias on the grid of. the tube 3! resulting in the tube 2'3 drawing less. anode. current and resulting in the tube 38' drawing more. anode current, so that the load. on the two. tubes tends to balance. In the same way, if the. tube. 3.6. draws more anode current than the tube 2.9,. the flow of cathode current through the

resistors

25 and 25 will result in the grid of the. tube 351 being biased more negatively, and will. result in the grid. of the tube 29' being. biased more positively, so that the anode currents tend to balance.

The; load inductances connected in the" anode circuits of the tubes may be the primary wind.- i'ngs of output transformers or may be tank coils, or other forms ofloads.

Each of the push-pull-connected tubes 29 and 30 of Fig. 2 may have other tubes connectedin parallel with it, as illustratedby Fig. l.

I claim as my invention:

1. An electrical system comprising a plurality of vacuum tubes having at least controlgrids,

Likewise, if the.

cathodes, and anodes; an anode voltage supply source; an output load circuit for said tubes; means connecting the anodes of said tubes through said load circuit to the positive terminal of said source; an independent bias voltage supply source having its negative terminal connected. to the control grids oi said tubes; resistors connecting said cathodes tov the positive terminal of said bias voltage supply source, bias resistors connecting said cathodes to the negative terminal of said anode voltage supply source, and an input. circuit connected to said grids.

2. An electrical system comprising a plurality of. vacuum. tubes having interconnected control grids andinterconnected anodes, and having cathodes; an anode voltage supply source; an output load circuit; means connecting said anodes through said load circuit to the positive terminal of said supply source; an independent bias voltage supply source having its negative terminal connected to said control grids; resistors connecting said: cathodes to the positive terminal of said bias voltage supply source, bias resistors connecting said cathodes to the negative terminal of said anode voltage supply source, and. an input circuit connected to said grids.

3.. An electrical system comprising a pair of vacuum tubes. having control grids, cathodes; and anodes; an input circuit connected pushpull to said grids; a load circuit connected pushpull to said anodes; an anode voltage supply source. having its positive terminal connected through said load circuit to said anodes; gri'd' resistors connected in series between said control grids; a bias voltage supply source having its negative terminal connected to the mid-point connection of said resistors; other resistors connected in series between said cathodes, the positive terminal of the latter said source being connected to the mid-point connection of said other resistors, and bias resistors connected in series between. said cathodes and having their midpoint connection connected to the negative terminal of said anode voltage supply source, there being no fixed electrical relationship between the negative. terminal of the bias voltage supply source and the negative terminal of the anode voltage supply source.

4. The electrical system of claim 2-, in which said control grids are directly connected to gether.

5. The electrical system of claim 2, in which said anodes are directly connected, together.

6,. The. electrical system of claim 2, in which said control grids are directly connected" together, and said. anodes are directly connected together.

NELSON B THARP;

References. Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,973,725 Ranger Sept. 18, 1934 2,123,241 Harley July 12,. 193% 2,337,918 Moyer Dec. 28, 1943 2,416,188 Mcle1lan Feb. 18, 1947