US2335168A - Exciter lamp for use in photoelectric devices - Google Patents

Description

Nov. 23, 1943. F. u. BINGLEY 2,335,168

EXCITER LAMP FOR USE IN PHOTO-ELECTRIC DEVICES Filed June 28, 1941 tions of the record grooves.

Patented Nov. 23, 1943 EXCITER LAMP FOR USE IN PHOTO- ELECTRIC DEVICES Frank J. Bingley, Chestn Philco Radio and Tele lit Hill, Pa., as signor to vision Corporation, Phila delphia, Pa., a corporation of Delaware Application June 28, 1941, Serial No. 400,315

This invention relates to incandescent exciter lamps for use in photo-electric devices adapted to produce audio-frequency currents.

The invention is particularly concerned with lamps of the above general character adapted for use in devices where it is desired to eiTect a very accurate modulation of the output of the photo-electric cell. An example of such a device is the photo-electric phonograph pick-up Thompsomfierial No. 357,322, filed September 18, 1940, wherein the entire photo-electric translating system is carried by a picloup head at one end of the tone arm.

Photo-electric pick-up devices of this character comprise a light source, a mechanical system for fluctuating the beam of light from said tion by the stylus in accordance with the undula- I have discovered that the lamp employed in a device of this character frequently gives rise in the audio frei1uency range. This action tends to produce undesired modulation of the cell output, and the undesired audio-frequency currents with respect to the mirror that the beam 2 Claims. (Cl; 1776-39) the massof the glass bead to I supporting wires form a vi-' bratory combination which has been found to be resonant within the audio-frequency band, giv

ing rise to pronounced vibration of the filament, ,Since, as will be seen from the later description,

the lamp and cell are preferably so adjusted of light v on and half ofi the cell, the filament vibration causes an undesirable m0dulation of the output of the photo-electriccell.

It is the primary object of the, present invention to overcome the aforesaid difiiculties by the provision, 111 a. lamp of the above type, of a novel thus produced are amplified and translated into sound.

found desirable to use a lamp of the type having a glass bead as mentioned above. However, in

electric cell 5.

filament support which raises the resonant frequency thereof outside of the audio band.

A more specific object of the invention is to provide a novel is substantially prevented. It is a further object of the invention to provide such a IlOl'l-IlliClOIJhOlllC lamp which may be inexpensively manufactured, .even in very small sizes.

The manner in which the above objects and advantages are realized will be best understood by reference to the following description vtaken together with the accompanying drawing, in

which:

Fig. 1 is a schematic representation of a phonograph pick-up device and associated amplifier, and shows the lamp of the invention applied thereto e l Fig. 2 is an enlarged cross-sectional view of the lampyarid.

Fig. 3 is av perspective view of. the filament support structure, taken from a dilferent angle to better illustrate the preferred positioning of the different elements.

Referring more particularly to the drawing, in Fig. 1 the pick-up, generally indicated at 2, is of the type disclosed in the above-mentioned Thompson application, and comprises an exciter lamp 3, a vibrating mirror 4, and a photo- Light from the lamp may be directed onto the mirror by means of a suitable lens system 6, the lenses and lamp being conventhe mirror, as pointed out above, that the beam of light is normally half on and half ofl the cell 5, so that when the pick-up is placed on a recording, the undulations of the record grooves will cause. the illuminated area of the cell to vary in accordance with said undulations. The electrical output of the cell may be applied to an audio amplifier H and thence to a. loud speaker l2. The lamp 3 may be energized from any suitable current source.

A brief consideration of Fig. 1 will serve to clearly indicate how vibrations of the lamp filament may cause distortion of the signal reproduced by the loud speaker. Sound vibrations transmitted from the loud speaker either directly, or through the cabinet structure, normally tend to cause vibration of the lamp filament, ment, which in turn efiects a modulation of the light falling on the photocell 5. The resulting signal is amplified and reproduced, and ii. this occurs in the proper phase, a sustained oscillation or howl may result.

Figs. 2 and 3 illustrate the exciter lamp of the present invention, which is particularly adapted to overcome the microphonic problem outlined above. I

This non-microphonic lamp comprises a generally pear-shaped envelope l3, fitted into a brass base I4, filled with basing cement l5, and capped with a black-glass insulator it, which also serves to hold and position the center contact eyelet H. In assembling the lamp, one of two lead wires l8-l8 protrudes through a central aperture formed in the black-glass insulator and into the eyelet I 7. Solder is then dropped into the eyelet from outside the lamp, and fixes the lead wire to the eyelet.

The other of the supporting-conducting leads i8 is soldered to the base shell M, and both leads are introduced through the envelope, as at B9, and extend upwardly through a glass bead it, to support and supply current to the filament 2B. A third wire or rod 22 has its upper end firmly embedded in the head 20 and extends downwardly through the envelope as at 23 and into The resonant frequency of a mechanical structure is expressed by the formula 1 F 21r \/1 lf where f is the resonant frequency, S is the stiffness, and M is the mass; It will be seen, therefore, that by increasing the stifiness S, the resonant frequency may be raised. The tripod structure of this invention imparts such stiffness to the filament support, in relation to its mass, that the resonant frequency is outside the audio-frequency range.

Preferably, the element 22 should be formed of wire of about the same size as the wires I8. In any event, these elements should have sufilcient rigidity to serve the desired purpose.

From the foregoing description, it will be seen that the invention provides a novel lamp which solves the troublesome problem of microphonics which arises in photo-electric devices of the type described. Moreover, the invention provides a construction which is relatively simple and inexpensive to manufacture.

It will be understood that the invention is not limited to the specific structure illustrated, but is capable of modification within the scope of the appended claims.

I claim:

1. A miniature incandescent lamp having a filament mount comprising a pair of lead wires held in spaced relation by a refractory bead and carrying a filament on their free ends, said lead wires being sealed into and passing through the neck of the bulb, and an anchor wire sealed to said bead at one end and sealed to the bulb neck at its other end substantially at the level of the seals of the leads and spaced therefrom to provide a three-legged support for the mount preventing the setting up of harmful vibrations, the seals of the leads and anchor wire to the bulb neck being spaced apart from each other a distance substantially of the order of the distance from said seals to said refractory bead.

2. An incandescent lamp comprising in com-' bination an envelope, a filament therein, a refractory bead supported by three wires sealed thereto at points out of line with each other to provide a three-legged mount therefor, two of said wires extending beyond said bead and serving as supporting and lead wires for said filament.

FRANK J. BINGLEY.

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