US3373364A

US3373364A - Standby cathode heating circuit for vacuum tube

Info

Publication number: US3373364A
Application number: US489626A
Authority: US
Inventors: Gerald A Tumarkin; Ng Walter
Original assignee: Griffiths Electronics Inc
Current assignee: Griffiths Electronics Inc
Priority date: 1965-09-23
Filing date: 1965-09-23
Publication date: 1968-03-12
Anticipated expiration: 1985-03-12

Description

G. A. TUMARKIN ETAL Filed Sept. 23, 1965 STANDBY CATHODE HEATING CIRCUIT FOR VACUUM TUBE g g i INVENTORS 627,440 A. TUMAAK/A/ 4 MA 76/? N6 BY M ATTORNEYs 99 Dunn ll 0x March 12, 1968 United States Patent Office 3,373,364 Patented Mar. 12, 1968 ABSTRACT OF THE DISCLOSURE An electric circuit employing electronic vacuum tubes with heated cathodes is quickly brought to operative condition through the use of a control switch by-passed by an inductance which inductance is the relay coil of a relay of which the contacts control the high voltage supplied to the tubes. When the switch is open, the high voltage to the tubes is cut off by the relay contacts opening and the current to the heaters is reduced because of the reactance of the relay coil. The low and high voltage supplied to the tubes may be through a transformer and the inductance lay-passed switch may be in the primary of the transformer.

This invention relates to a circuit for altering the turn on characteristic of an electronic circuit employing heated cathodes and in which the current to the heaters of the cathodes is obtained through a transformer.

Electronic equipment or sets such as television and radio sets employing vacuum tubes, particularly with indirectly heated cathode-s, are not instantaneously responsive to the turning on of the switch to the set, nor to the flow of current through the tube heaters since an appreciable time must elapse before the cathodes are heated to a state wherein suflicient electrons are emitted to enable current conduction through the vacuum tubes.

It is an object of this invention to create a circuit which will eliminate the delay normally ensuing after the turning on of a control switch in a circuit employing heated electron tubes before the circuit is rendered effective.

In a spcific aspect, the invention consists in the use of a relay, the coil of which is in series with the primary winding of a step-down transformer and bridges the switch. The contacts of the relay, which are normally closed, are in series with the mid-tap of a high voltage winding on the transformer and ground, the high voltage winding being employed for supplying high voltage to the tubes. Upon energization of the coil, by opening of the switch, the relay contacts are opened disrupting the high voltage supply in the set.

FIGURE 1 represents a conventional power supply of electronic equipment utilizing vacuum tubes and some vacuum tubes utilized in the set with heater supply lines thereto.

FIGURE 2 shows a circuit in accordance with this invention.

Referring to the drawings in greater detail, in FIG- URE 1 there is illustrated a power supply of a radio, television or the like. This power supply normally utilizes a transformer having a primary 12 of many turns, a center tapped high voltage secondary 14 of many more turns than the primary winding and at least one low voltage winding 16 of much fewer turns than in the primary winding to supply current to the heaters in the vacuum tubes 17 of the electronic set. Usually a second low voltage winding, as winding 18, is employed to provide heating current for the cathode in the rectifier tube 20, independently of the heater current supplied by winding 16 to the heaters in the other tubes 17 of the set. A switch 22 is in series with a pole of the plug 23 and the primary of the transformer to control set operation. The lead from the rectifier cathode or heater of the rectifier is at high positive potential (B plus) and the current in that lead is usually filtered by a filter comprised of

capacitors

24 and 26 and an inductance 23. The negative lead of the high voltage supply is normally grounded to the chassis of the set, as is one side of the low voltage or A supply. The mid tap of the high voltage secondary coil is usually grounded via a line 30. A fuse 32 or equivalent is employed in the transformer primary circuit to protect the set against excessive current flow therethrough.

The circuit of the invention is shown in FIGURE 2. This circuit differs from that shown in FIGURE 1 in the bridging of the switch 22 by the coil winding 34 of a relay, the armature contacts 36 of the relay being cut into the line 30. The spring contacts are normally biased to closed position but are held open when switch 22 is open. When switch 22 is closed, the relay coil is shorted out, the relay is de-energized and the contacts close. i

The application of the relay to an existing circuit such as is shown in FIGURE 1 is thus very simple, merely necessitating the bridging of the terminals of switch 22 by the coil winding of the relay and the interposition of contacts 36 of the relay in the wire 30, or removing wire 30 from ground and attaching it to one contact of the relay and grounding the other contact.

In use of the circuit of FIGURE 2, when the switch 22 is open, the set is inoperative. At this time the reactance of the inductance inserted in the circuit, here illustrated as relay coil 34, is in series with the reactance of the primary 12 of the transformer 10 and the voltage across the primary is reduced. Therefore the voltages in the secondaries are reduced proportionally. Also since with the switch 22 open the relay coil is energized sufficiently to open the relay contacts 36, the ground circuit to the set has been disrupted and no high voltage or B current can flow through the circuit, thus removing B voltage from the anodes, this occurring when the tubes are otherwise not conditioned for controlled current conduction therethrough.

When the switch 22 is closed, the reactance of coil 34 is shorted out of the circuit and full potential is applied to the primary of the transformer and therefore normal operating potentials are applied to the vacuum tubes in the set, the contacts 36 being released to their spring action to close and to thereby establish the high voltage or B circuit.

In a practical application of the device the relay coil is in circuit with the primary of the transformer and is designed to create a 25% drop in the direct line voltage appearing across the primary, producing corresponding voltage drops in the several secondaries. Under operating conditions of the set, switch 22 is closed and the voltage developed by winding 18 is 5 volts. Under inoperative conditions of the set, that is to say with switch 22 open, the voltage developed by winding 18 is about 3.75 volts. Similarly while the normal voltage across winding 16 is 6.3 volts, with switch 22 open it will be about 4.725 volts.

Having thus described the invention, what is claimed as the invention is:

1. In an electronic circuit employing at least one vacuum tube having a heater and high voltage electrodes, a circuit means for supplying both current to said heater and high voltage to said electrodes, a switch in said circuit means for closing said circuit means, an inductance bridging the switch whereby when the switch is open the reactance of the inductance and the remaining portion of the circuit means maintains the voltage across the 3 heater at a value ins-ufficient to cause effective electron emission in the tube and when the switch is closed the inductance is short circuited to cause effective electron emission within the tube, and said circuit means including a second switch with open contacts in the high voltage supply means when the first switch is open, said inductance being the relay coil of a relay Whose contacts are the contacts of the second named switch, whereby the high voltage supply means to the high voltage electrodes is open when the first switch is open and closed when the first switch is closed.

2. A circuit as defined in claim 1 in which the high voltage supply means includes a transformer having a winding, a terminal of which forms one pole of the high voltage supply, said winding having a tap which forms a second terminal of the high voltage supply, a line connecting said tap to an electrode in said tube, said second switch being connected in series in said line.

References Cited UNITED STATES PATENTS 2,872,573 2/1959 Wilson 328-270 3,171,084 2/1965 Sziklai 328-270 3,225,302 12/1965 Ojelid 328-270 'DAVID J. GALVIN, Primary Examiner.