US2215521A

US2215521A - Vacuum tube filament supply

Info

Publication number: US2215521A
Application number: US208964A
Authority: US
Inventors: Finch James Leslie
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-05-20
Filing date: 1938-05-20
Publication date: 1940-09-24
Anticipated expiration: 1957-09-24

Description

Sept. 24, 1940. J FNCH 2,215,521

' VA UUM TUBE FILAMENT SUPPLY Filed May 20, 1938 2 Sheets-Sheet l INVENTOR.

. JjgES L. F/NCH I 0 BY SEC. 360

ATTQRNEY.

Sept. 24, 1940.. J F|NH 2,215,521

VACUUM TUBE FILAMENT SUPPLY Filed May 20, 1958 2 Sheets-Sheet 2 INVENTOR. JAM/4Z5 L. F/NCH A TTORNEY.

Patented Sept. 24, 1940 UNITED STATES VACUUM TUBE FILAME'NT'SUPPLY James Leslie Finch, Patchogue, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 20, 1938, Serial No. 208,964

11 Claims. My invention relates to audio frequencyand radio frequency power amplifiers in which 2.1--

ternating current is used to heat the filaments of the vacuum tubes. In radio frequency power amplifier applications it relates particularly to those services in which the modulation resulting from the A. C. filaments is objectionable such as in connection with telephone service. Polyphase filaments are already in use for the purpose of affecting a reduction in the modulation due to V the A. C. filaments. My invention resides in an improved method of using polyphase filaments for further reduction of this modulation.

In the prior art tubes having polyphase filaments composed of six filament wires, one end of each being connected to six external filament terminals and the other end of each being connected to an internal neutral point are well known. Three phase filament power is used with these tubes in which the filament wires are connected in pairs, each pair forming one leg of a three phase star circuit. They are also used with six phase power, in which case each filament wire forms a leg of a six phase star circuit though this six phase connection results in no material improvement over the three phase con-' nection. The reason for this will be understood from the following analysis.

Modulation of the plate current and modulation of the amplified radio frequency current by the A. C. filament current is largely due to the magnetron effect of the current. The filament current in each filament wire sets up a magnetic field around it. This field tends to deflect electrons leaving the filament and to impede their travel toward the plate. The higher the filament current the greater this effect becomes. This results in a modulation of the plate current and of the gain of the amplifier when alternating current is used in the filament. The frequency of this modulation is twice that of the filament current because the efiect of the current is practically thesame regardless of its direction. Thus for 60 cycle filament current the output/from the portion of the tube corresponding to each filament wire is modulated at a frequency of 120 cycles and at frequencies which are harmonics of 120 cycles. When three phase, 60 cycle fila- 50 ment current is used the resulting 120 cycle modulation in each leg is displaced one-third of a cycle from that of the other legs. This results very largely in a cancellation of the 120 cycle and 240 cycle components and leaves the 55 360 cycle. and higher frequency components inthe output as the only ones of any material consequence. When six phase filament current is used no material improvement over three phase is obtained because with the six phase connection there is no difference in the filament cur- 5 rents except that the current in one of each of the pairs referred to above is in the opposite direction from that in the other wire of the pair. Thus the modulation components of 360 cycles and its multiples are present in the output in essentially the same way as when three phase power is used.

In my invention I connect the six filament terminals of the tube heretofore described to a specially connected transformer whereby the 360 cycle components of the modulation are also largely cancelled leaving only the 720 cycle components and multiples of 720 cycles.

A better understanding of the present invention will be had by reference to the following detailed description, which is accompanied by drawings in which,

Figure 1- is a circuit diagram of the primary and secondary of a filament transformer connected in accordance with my invention.

Figure 2 is a connection diagram of the same transformer. 1

Figure 3 is a circuit diagram similar to Figure 1 of an alternate connection for obtaining the desired phase relations.

Figure 4 is a circuit diagram of the internal connections of the tube with which my invention may be used and the connections of said tube to the transformer.

Figure 5'is a graph explanatory of the operation of my invention.

Figures 6 and 7 are circuit diagrams of the primary and secondary of a pair of transformers which may be used with a modification of my invention using two tubes, while Figures 8 and 9 show a modification of the invention shown in Figures 6 and 7.

Referring, now, to Figure 1 which is a conventional circuit diagram of the primary andsecondary of the filament transformer connected in accordance with my invention, numerals I, II and III designate the delta connected primary of the transformer. Obviously, of course, the primary may be connected in a star connection if so desired. The secondary is connected in; a star arrangement as shown with the neutral point 11. and output terminals, a, b; c, d, e and f. The angular phase relationship between the currents from these output terminals is indicated in the "tubes for this modification may be obtained in dashed lines a, b,

*ing

drawings. It will be seen that the phase relationship between terminals 11. and b is 30 degrees. Likewise, the phase relationship between 0 and d, and e and f is also 30 degrees. Between terminals b and c, d and e, and f and a, the phase relationship is 90 degrees.

In Figure 2 is shown the connection diagram of the same transformer as schematically shown in Figure 1. The same reference letters are used as in Figure 1.

Figure 3 shows an alternate secondary connection for obtaining the required phase relationship for the practice of my invention. A delta connected secondary is shown which may be substituted for the star connection shown in Figure 1. The same reference letters for the terminals are used as in Figure 1.

In Figure 4 I have shown a circuit diagram .of the internal connections of the tube with which my invention may be used. The filament wires denoted by reference letter I are all connected together at a central neutral point 0. The free ends of each filament wire are led out to terminals 1 to 6, inclusive. These terminals are a connected to the terminals a to ,f, inclusive, of

the transformer as shown in this figure.

In Figure 5 I have shown in a graphical form the relationship between the currents in the six filament wires plotted against time. These currents are represented by the: solid lines lettered a, b, c, d, e and 1. Since, as explained before, the direction of the current at any'instant of time has no influence on its effect in the tube d, e and f are drawn in a reversed position to indicate the negative halves of the filament currents. Thus, the solid and dashed lines above the zero line indicate the effective currents as regards their tendency to produce modulation. It will be noted from an inspection of this figure that all modulation frequencies below the twelfth harmonic, that is, 720 cycles, tend to be cancelled.

In one modification of my invention I may use two tubes or two sets of tubes in one amplifier circuit with a pair of filament transformers so connected that the phase relationship of the currents in one tube or set of tubes is offset 15 degrees from that in the other tube or set of tubes. This tends to cancel the twelfth harmonic leavonly the twenty-fourth harmonic (1440 cycles) and its multiples to effect the resultant output. This 15 degree phase relation may be obtained with the filament transformer connected to one tube or set of tubes, as shown schematically in Figure 6, and the other connected as in Figure '7. The same reference letters appear in these figures as in Figure 1, however, subscripts 1 and 2 have been added to clearly indicate that the transformer in Figure 6 is connected to one tube or set of tubes and the transformer in Figure 7 to the other tube or tubes.

The desired 15 degree phase relationship between the filament current in the two sets of another way as shown in Figures 8 and 9. In the modification, as shown in these figures, the advantage is obtained that two identical transformers may be used, the only change being in the external connection of the transformer windings. This is apparent from Figures 8 and 9 where the angular relationships are clearly shown.

While I have shown and described insome detail several modifications of my invention, it is to be clearly understood that my invention is not limited thereto but that modifications within the scope of my invention may be made.

I claim:

1. In combination, a vacuum tube having a polyphase filament with six legs connected in a star configuration about a common neutral point, each leg having an-external connection, a source of three phase power, means for deriving the first, second, fifth, sixth, ninth and tenth phases of a twelve phase polyphase current from said source of three phase power and means for supplying each of said phases to alternate ter- -minals of said filament.

2. In combination, a vacuum tube having a polyphase filament with six legs connected in a star configuration about a common neutral point, means for supplying alternating current to each leg of the said filament, the phase relationship between the currents in each of five of said legs to the sixth being substantially 30, 120, 150, 240 and 270 degrees, respectively.

3. In combination, a pair of vacuum tubes each having a polyphase filament with six legs connected in a star configuration about a common neutral point, separate means for supplying alternating current to the filaments of each of said tubes, the phase relationship between the currents in each of five of said legs to the sixth of each tube being substantially 30, 120, 150, 240 and 2'70 degrees and the respective phases of the current suppliedto one tube of the pair being advanced substantially 15 degrees from that of the other tube.

1. In combination, a pair of vacuum tubes each having a polyphase filament with six legs connected in a star configuration about a common neutral point, separate means for supplying alternating current to the filaments of each of said tubes, the phase relationship between the current in each of five of said legs to the sixth of each tubebeing substantially 30, 120, 150, 240 and v2'70 degrees and the respective phases of the current supplied to one tube of the pair being advanced an odd multiple of 15 degrees from that of the other tube.

5. In combination, a vacuum tube having a polyphase filament with six legs connected in a star configuration about a common neutral point and each leg having an external terminal, a source of alternating current power, a polyphase transformer having its primary connected to said source of power and a plurality of secondaries, connections from each pair of alternate terminals of said filament to a secondary winding of said transformer, the connections being so arranged as to impress polyphase voltages on the filament legs with phase relationships of substantially 30 degrees between each of three pairs of legs and 120 degrees between each of these pairs and the other pairs.

6. In combination, a pair of vacuum tubes each having a polyphase filament with six legs connected in a star configuration about a common neutral point and each leg having an external terminal, a source of alternatingcurrent power and a pair of polyphase transformers, each transformer having its primary connected to said source of power and each transformer having a plurality of secondaries, connections from each pair of alternate terminals of the filament of each of saidtubes to a secondary of its respective transformer, the connections being so arranged as, to impress polyphase voltages on the filament legs with a phase relationship of substantially 30 degrees between each of three pairs of legs and 120 degrees between each of these pairs and the other pairs of legs, the respective phases of voltages supplied to one tube of the pair being advanced substantially 15 degrees from that of the other tube.

7. In combination, a pair of vacuum tubes each having a polyphase filament with six legs connected in a star configuration about a common neutral point and each leg having an external terminal, a source of alternating current power and a pair of polyphase transformers, each transformer having its primary connected to said source of power and each transformer having a plurality of secondaries, connections from each pair of alternate terminals of the filament of each of said tubes to a secondary of its respective transformer, the connections being so arranged as to impress polyphase voltages on the filament legs with a phase relationship of substantially 30 degrees between each of three pairs of legs and 120 degrees between each of these pairs and the other pairs of legs, the respective phases of voltages supplied to one tube of the pair being advanced an odd multiple of 15 degrees from that of the other tube.

8. In combination, a pair of groups of vacuum tubes each tube having a polyphase filament with six legs connected in a star configuration about a common neutral point, separate means for supplying alternating current to the filaments of each of said groups, the phase relationship between the currents in each of five of said legs to the sixth of each group being substantially 30, 120, 150, 240 and 270 degrees and the respective phases of the current supplied to one group of tubes being advanced substantially 15 degrees from that of I the other group.

the current supplied to one group of tubes being advanced an odd multiple of 15 degrees from that of the. other group.

10. In combination, a pair of groups of vacuum tubes each tube having a polyphase filament with six legs connected in a star configuration about a common neutral point and each leg having an external terminal, a source of alternating current power and a pair of polyphase transformers, one transformer for each group of tubes, each transformer having its primary connected to said source of power and each transformer having a plurality of secondaries, connections from each pair of alternate terminals of the filaments of one of said groups a secondary of its respective transformer, the connections being so arranged as to impress polyphase voltages on the filament legs with a phase relationship of substantially 30 degrees between each of three pairs of legs and 126 degrees between each of these pairs of legs and the other pairs of each tube, and the respective phases of voltages supplied to one group of tubes being advanced substantially 15 degrees from that of the other group.

11. In combination, a pair of groups of vacuum tubes each tube having a polyphase filament with six legs connected in a star configuration about a common neutral point and each leg having an external terminal, a source of alternating 'cur.

rent power and a pair of polyphase transformers, one transformer for each group of tubes, each transformer having its primary connected to said source of power and each transformer having a plurality of secondaries, connections from each pair of alternate terminals of the filaments of one of said groups to a secondary of its respective transformer, the connections being so arranged as to impress polyphase voltages on the filament legs with a phase relationship of substantially 30 degrees between each of three pairs of legs and 120 degrees between each of these pairs of legs, and the other pairs of each tube, and the respective phasesof voltages supplied to one group of tubes being advanced an odd multiple of 15 degrees from that of the other group.

JAMES LESLIE FINCH.