Hanert Electric Orchestra

John M. Hanert was de hoofd-ingenieur en ontwerper bij de Hammond Organ Co. van 1934 tot zijn overlijden in 1962.

Hieronder John Hanert, samen met Laurens Hammond, werkend aan zijn (boven) Solovox en (onder) Novachord.

 


 
De synthesizer van Hanert of  "het Elektrische orkest" werd ontworpen en gebouwd door John Hanert in 1945 voor Hammond en werd beschreven als een "Apparaat voor automatische productie van muziek". Deze synthesizer was een instrument voor het componeren en de maken van de klank-synthese van elektronische muziek, net als de later beroemde RCA synthesizer en andere, soms enorme, machines.



In plaats van geponsde papieren tapes op rollen, welke de RCA-synthesizer (boven) met veel rompslomp gebruikte, had de Hanert -synthesizer een bewegende, mechanische scan-kop met electrisch gevoelige borstels, die boven een 20 meter lange tafel bewoog over 11 en 12-inch papieren kaarten. De papieren kaarten bevatten de kenmerken van het geluid (toonhoogte, duur, timbre en volume), die waren opgeslagen in de vorm van grafiet markeringen die gelezen werden door de elektrische scan-kop, tesamen met de informatie van de af te spelen muziek. Het leuke was, dat veranderingen gewoon met een simpel potlood konden worden toegevoegd. Het werkte een beetje als een barcode systeem. Let wel, het was in 1945.

Hier de tafel van boven en van opzij. Wellicht bevat het "karretje" linksonder de bewegende aflees-kop.



De geluidsgenerator van dit instrument bezette een hele kamer en bestond uit een blok van vacuümbuis oscillatoren, een random frequency generator (voor de 'white noise' kenmerken voor percussie geluiden) en "wave shaping circuits". Versnellen en vertragen van de afgespeelde muziek (accelerando/decelerando) kon worden gecontroleerd door middel van wijziging van de snelheid en richting van de scan kop.
Ook konden de kaarten verwisseld worden, zodat je een andere muzikale compositie kreeg.

Het instrument is daadwerkelijk gebouwd, maar helaas zijn er alleen nog de patenten en beschrijvingen van over. We gaan ze bekijken. Eerst de uitgetypte teks van het patent.

"In the method and apparatus of this invention the composer, arranger or conductor has at his command means for controlling the quality of each note, its intensity, envelope and the degree of accent, duration and tempo without necessarily affecting any other note or tone of the composition. he has under his control, within the limitations imposed by the apparatus as a whole, facilities for producing, under his sole control, any of a substantially infinite variety of renditions of a composition.”


Beschrijving (deze OCR-scan van de tekst bevat helaas nogal wat fouten)

Feb. 13, 1951 J. M. HANERT APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC 11 Sheets-Sheet 3 Filed Nov. 1, 1945 Xbm Feb. 13, 1951 J. M. HANERT APPARATUS FOR AUTOMATIC PRODUCTION OF Music Filed Nov. 1, 1945 ll Sheets-Sheet 4 Ill.

KWM

J. M. HANERT 2,541,051

APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC Filed Nov. 1, 1945 Feb. 13, 1951 11 Sheets-Sheet 5 J. M. HANERT APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC Feb. 13, 1951 11 Sheets-Sheet 6 Filed Nov. 1, 1945  J. M. HANERT APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC Feb. 13, 1951 11 Sheets-Sheet 8 Filed Nov. 1, 1945 11 Sheets-Sheet 9 J. M. HANERT Feb. 13, 1951 APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC Filed Nov. 1, 1945  John M. HANERT 2,541,051

11 Sheets-Sheet 10 APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC  Feb. 13, 1951 Filed Nov. 1, 1945 Patented Feb. 13, 1951 APPARATUS FOR AUTOMATIC PRODUCTION OF MUSIC John M. Hancrt, Park Ridge, 111., assigned Hammondlnstrument. Company, Chicago, 111., a. corporation-of Delaware Application November 1, 1945, Serial No. 626,150

28 Claims.

"My lnvention relates generally to apparatus for production as sound or as a signal for recording purposes, without the employment of musicians in anyway whatsoever. In other words, the in" vention contemplates that'a composeror-arranger may, using the apparatus ofthe invention, score the musical composition, whereupon the music will be producedautomatically by the apparatus with all the variations usually present in orchestral renditions of music, such variations being in pitch and tone quality, in volume, in accent of individual notes, in tempo, and in tone intensity envelopes."

While some features of the invention are applicable to the control of conventional mechanicaland electrical musical instruments, the invention is herein illustrated as applied to the control of electronic musical instruments and apparatus It is thus among the objects of the invention to provide:

1'. An apparatus whereby a suitable record marked upon paper or the like and representing all of the character-istcs oi'tone quality, of tone intensity envelope, accent, tempo and the like may be automatically translated into electrical signals representative of an orchestral rendition of a musical composition;

2. An improved means for producing a record of the musical score;

3. An improved means for controlling the output of a plurality of electrical musical instruments;

4. Improved means for detecting and translating a musical score marked on paper into signals utilizable for the control of musical instruments;

.5. An improved'apparatusin which one record may be used to control the pitch, accent and the like whereas another marked recordis selectively operated by the first marked record to secure predetermined changes in the instrumentation, vibrato and volume;

6. An improved apparatus for securing a multiplicity of predetermined, changes in tone quality, tone intensity envelope, accent, tempo, vibrato and like by means of a single mark on the main controlling record;

7.. An improved record of paper or similar material composedof a plurality of cards overlapping in a shingle-like manner soas to form a long record-in which shrinkage of the paper or  2 other material does not have any appreciable effect;

8. A series of overlapping tables for supporting the record whereby leveling of the tables is facilitated;

9. An improved notation card having imprinted thereon a set of timing or rhythm markings and. a set of note "position markings extend ingv perpendicular to. the timing or rhythm marklugs;

10. An improved scanner mechanism operating in timed sequence for sensing the musical notations marked upon the record cards;

11. An improved scanning, mechanism. which does not injure, obliterate or otherwise render ineffective the scored musical markings even though used repeatedly;

12. An improved electrical transducer for converting the scanned markings into corresponding changes in electrical current flowing through an electronic load circuit;

13. An improved alternating current generating system producing musical tone frequencies with means for transmitting, collecting, and controlling the intensity envelope characteristics of the tones by a direct current determined by a scanning mechanism;

14. An improvedlorchestral, registration and control table having means for moving it in response to score markings;

15. An instrumentality of the above mentioned, type in which the overall expression in the output is control ed by markings on a record; and

1.6.. An improved record scanning mechanism in which the speed of scanning is controlled by markings on the record being scanned.

Other objects. will appear from the following, description, reference being .had to the accompanying drawings in which:

Figure l is .a schematic diagram showing the relationship of the-various components of the complete apparatus;

Figures 2, 3, 4 and 5 are schematic diagrams of various forms of scanning circuits and associated elements;

Figure 16- is aschematic diagram of the circuit employed to operate the solenoidoi the instrumentation sequence table under the control of mark ngs on vtl-lerecord Figures '7 and 8 are schematic diagrams of the circuits and associated elements of two modified tor-ms of scanning apparatus;

Figure 9 is a plan view of thetime sequence or record supportingstable;

Figure is a side elevational view of said table;

Figure 11 is an enlarged fragmentary sectional view taken on the line l I of Fig. 9 and showing one of the record card locating pins;

Figure 12 is a plan view of the instrumentation sequence table;

Figure 13 is an end elevational view taken on the line l3 of Fig. 12;

Figure 14 is a plan view of one of the record cards showing exemplary control markings thereon;

Figure 15 is a schematic wiring diagram showing the circuits for producing accents and for causing changes in overall volume of the output;

Figure 16 is a schematic circuit diagram of the coupler system and the means for controlling the transmission of tone signals to the output system;

Figure 17 is a schematic wiring diagram showing the means for producing Xylophone-like tone envelopes;

Figure 18 is a schematic diagram showing the circuits and associated elements for producing sustained tones;

Figure 19 is a schematic diagram illustrating the means for controlling the production of percussive effects such as drums and the like;

Figure 20 is a schematic diagram showing the circuits and associated elements for controlling tone quality;

Figure 21 is a schematic diagram showing the means for causing acceleration and deceleration of the scanning apparatus relative to the record; and

Figure 22 is a schematic diagram showing a modification of the means for sensing card notations.

General description: It is customary practice in the production of orchestral music for the composer to write the original score, possibly with only infrequent notations as to the instrumentation to be employed, and in some instances without any instrumentation. This score is then used as a guide by the arranger (who may also be the composer) and the scores for the various instruments of the orchestra are written, usually a separate score for each instrument of the orchestra by which the composition is to be rendered. In music to be arranged for an orchestra of a large number of pieces this is a tedious process, while it nevertheless requires a high degree of artistry and skill.

Thereafter the arrangements of the musical compositions are utilized by the members of the orchestra for rehearsal and final rendition of the composition. The composer ultimately usually has but slight control over the instrumentation employed by the orchestra and it is only after these tedious and time consuming steps have been taken and the orchestra ultimately renders the composition that the com oser can actually audition his composition played in the manner the public may be ex ected to hear it.

Especially in the making of phonographic or similar sound recordings frequent rehearsals are necessary in order to assure that the recording made will accord with reasonable fidelity with the ideas of the composer and orchestra conductor as to how the composition should be interpreted and rendered. In actual practice it is seldom that a recording represents the closeness to perfection which is anticipated by the composer and conductor, since in each rendition by an orchestra a fault or imperfection in technique by one or more of the musicians is likely to manifest itself. In endeavoring to correct the faults of a previous rendition, the conductor is likely to find that other faults have insinuated themselves.

The difficulties inherent in the orchestral production of a composition may be compared to those which would confront an artist who found it necessary in painting a picture to destroy the complete or partially complete picture he was painting every time he became dissatisfied with any slight detail of the picture. The painter is not subject to such stringent regulation but instead merely repaints such minor portion of the whole picture which does not represent the subject being painted sufficiently accurately to meet his artistic approval. In endeavoring to make a musical phonographic recording, the artist conductor does not have this opportunity to erase and correct slight blemishes in details but instead must rehearse the orchestra repeatedly until the complete composition can be rendered in reasonable compliance with his artistic concept of how the rendition should sound.

In the method and apparatus of this invention the composer, arranger, or conductor has at his command means for controlling the quality of each note, its intensity, intensity envelope, the degree of accent, duration, and tempo without necessarily affecting any other note or tone of the composition. He thus has under his control, within the limitations imposed by the apparatus as a whole, facilities for producing, under his sole control, any of a substantially inr finite variety of renditions of a composition.

In actual practice it has been found that it is not ordinarily practical to provide too many separate instrumentalities for producing the tone frequencies and controlling their various characteristics such as quality, tone intensity envelopes and the like, since in the music ultimately produced, even the most trained musician cannot detect minor changes in these qualities of the music. Since most auditory as well as other perceptions are governed by th Weber-Fechner law that the stimulus must increase in geometrical steps to cause noticeable difference in sensation, the number of steps of gradation in volume, degree of vibrato, change in intensity envelope, and changes in tone quality, need not be very great.

The apparatus includes means for supporting marked notation or record cards, comprising a long sectional table having rail along its longitudinal edges for a motor driven scanning carriage. The record notation cards have suitable perforations cooperating with locating pins projectin upwardly from the table, the cards being laid on the table in overlapping shingle fashion. The cards may be of any suitable size, one practical size being approximately 11" x 12". The cards suitable markings indicating the measures of the music to be scored thereon, each measure being divided into quarter tones, 8th tone intervals as well as making provision for triplets aggregating a quarter tone. In aggregate length there are suificient cards (39) to score a composition of at least 96 measures. For convenience there are three cards side by side to accommodate the usual number of required varieties in orchestral control. In addition, there are provided two instrumentation control cards which are located on a separate instrumentation table and coopcrate with a separate scanning apparatus.

In scoring a composition to be produced the composed or arranger may suitably mark cards in aznackz'and: by'rmaztltine the-cards tondicater hei order-.1 in. which; thev, are to; he; played. up  tables,. they may beinitially scored, by the composer.or arranger at his home or desk. The scoring? mayhegefiec-tediira; variety or ways; as by marking -the cardswith; asuitable graphite pencil to make an electrical conducting: mark, or; by using; a; conducting ink such. as a?quick; drying aquadega solution.if the useof a pencil. has beenfound; most practical. because of ther-ease with through-a suitable electrcmagnetically operated eseapement mechanism. Thus whenever a major change of instrumentation is desired amarlrwill:

lie-placed upon the notation cards-to cause advancing ofa the instrumentation sequence-scanner one tep The latter scanner is similar to that of the notation scanner but the relays operate dunden its control .efiect more or less-overall changes in -.instrumentation. and vibrato and. the like.

Accent and overall outputvolume may be controlled from the notation cards. The output is supplied to a monitoringspeaker and to a phonographic or similar recorder tenths-production of a mastery record from which the usual commercial pressings or other reproductions maybe made.

Lay outof apparatus: The overall layout of the apparatus best  be understood by the reference to Fig. l in which" the carrangement is diagrammatically illustrated. The timesequence table 35.; hears the notation cards. which control the operation of-thetime se quence scanner 32. This scanner operates through relays and solenoids to control'the operation. of the. instrumentation sequence table 34, with its scanner .36, as .well as to control the openation of direct current control systems I; II, III- and lV illustrated as bloc lrs Al, 42, lit-and 44.

Furthermore, relays controlled by thescanner 32 control accent systems I to IV illustrated inv Fig.1 as clocks El, 52. 53and, respectively. In addition-,..the scanner 32. controls the operation of an overall expression control 56.

The instrumentationsequence scanner controls. the.vibrato.introducing. means 65, 62, 63 and E i respectively for the tonegenerating;systemsl. to IV shown as blocks H to lfi. In addition, an instrumentation frequency scanner controls the operation of tone quality systems I to IV shown as blocks Site 84 and volume systems I to IV shown as blocks 9% to 94 respectively in Fig. 1. Eachoi-the-tone generating systemsli to ls suppliesmusical tim si nals to. he-dir ct current.

controlsystems .415 toldd,. respectively; and the signals from: the latterare. supplied to the tone ualitysystem sfll-to respectively; Ass modificdby" the tone qualitysystems, the signal issunplied to the accent systems 51 to 54-, and-the output thereof; is. amplitude. controlled lav-the: volume system, The c utput s of; the latter. volume: ey s. terns-are. supplied-to; the expression control. appaz ratusifizand the signelfromthe latterapparatus:

The relays operate to connect the 3; isasupplieeh thmu hr. an. oupuirsy em 9.5.. toa res cordec 9.51 or monitoring speaker; 91 or. both, def pending uponz the: positions, or. manually operated:- switchesrtfizandfit.

Scanningapparatus: The notation cards which are placed upon the timesecuence table was Well as the instrumentation determiningcards mounted on the instrumentatio'n sequencetablo are preferablyof' the general formindicated inFig 14'. The card I00 shown in Fig. 14 is provided with a: locating apertnrei il l and" an alignment aperture ii to main-- instrumentation sequence table. The details of thema ikings appearing on the cards tilt of Fig; willi be described hereinafter out it will be noted 'that the card is provided with a pluralityoi' markings such: as that; these markings-being of graphite, aquadag or  conductingmaterial which maybe readily an lied to the cards.

The scanningapparatus shown inFig. 2 com-- prises a pair-of contact brushes 166, which may I hev inwthe form of thin wires of Phosphorbronze or similar: resilientconducting 'material, and are arrangedito brush along the surfaces of the cards Hill: as the scanning apparatus moves along the time sequence table. (or as the instrumentation sequence table moves past its scanner). Upon" passinga conducting mark 5% on a card: associated'with a pairof the contact brushes [96; a circuit. from the positive terminal of a source of plate current [06 to the control grid Hii -of a pentode H2 is completed, this circuit including asuitable series grid. resistor R! M. When the contacts 596 are. not in engagement with a conducting mark, the pentode I I2 is'negativelyhiased" substantially to or beyond cutoff by connection of thegrid' l lilto the negative terminal oi 'abias battery H t; the connection-to the grid 1 it being through the resistor R514 and a resistorRHfi, the latter having acapaoitor Clfl'l in shunt there with; The cathode and suppressor grid of the pentode '2' are illustrated. asv connected to ground, this being the potential of the-negativetermi nal ofthe'voltage source I08 and the posi tive terminal of' the biasing voltage source I I6. The-screen grid'of this pentocle is connected to the=positive terminal of the plate voltage source H38.

A direct current control circuitimpedance i1 lustrate'das aresistance R! i8 is connected between the plate of the pentode H2 and the positive terminal oithe source Hi3, while a control means 4 L44, which may or may not include a relay (as will appear from thedescription of Figs. 6 and 3), is connected across the plate load resistorRllc ofthe pentode H2. This means controls thetransmission of tonesignals from a tone generating-system i'! to id-to a transmission means i255, which-may he considered as comprising elements contained in blockaE-i-Bd; 5I54, S t-At, 56. Q5 and 91. I lt wilrbe apparent froma consideration of the circuit shownin Fig. 2 that-when contactbetweenbrushes iilfi is completed by engagement of conducting'marlc M on one of the record notation cards Hit, the grid iii) will rapidly shift positive with respect to the cathode of thepentocl'e llZ causing a sudden flow of plate current; The resulting dropin voltage across the impedance RI 2% provides a substantial signal impulse through. the conductor H9 which connects-the plate oft pentode- I i-2' with the control means tain it in proper position on the time sequence or 4I-44. As a result, the wires I I9 may be long and those for the various pentodes II2 (of which there are in the illustrated embodiment I68 in the time sequence scanner and I I2 in the instrumentation frequency scanner) may be joined in a cable without danger of interference by inductive or capacitative coupling between the individual wires or of resistive leakage. The plate current drawn by the tube H2 is relatively constant and independent of the actual impedance at the pencil marks, being, in all cases, limited by the series grid resistor Ri I4 to that value that just corresponds to the initial flow of grid current.

In some instances it may be desirable to couple the contact brushes I06 directly to the control means, as illustrated in Fig. 3. In this figure the signal from a source such as 1I-14 is impressed directly across the input circuit of a non-linear control pentode I22, the character of the input signal being capable of being modified to some extent by closing a switch I24 to connect a capacitor (H25 in parallel. with a capacitor CI26 and with a grid resistor RI28. The contact brushes I06 control the potential of the cathode from a value beyond cutofi to a suitable operating potential by connecting the cathode to a suitable negative potential source, shown as a terminal -135 v., through an appropriate tonal envelope attack and decay network comprising capacitors CI30 and CI3I and resistors RI32 and RI33. Suitable operating potentials are applied to the remaining electrodes of the pentode I22, the plate potential being applied through load resistor RIM. The signal. appearing across the load resistor RIM is impressed upon the transmission means I20.

In operation, completion of a circuit across the contact brushes I06 results in increasing the cathode to screen potential on the pentode I 22, thereby to cause plate current how at a rate determined by the mesh CI30, CI3I, RI32, Rl33, and upon breaking the circuit between the brushes I06 the cathode potential will increase at a rate, determined principally by the values of CI30 and RI33, to a value where screen and plate current cease to flow. CI3I will ordinarily be small relative to CI35] and is provided mainly to prevent undesirably rapid transients. Thus the signal originated in the generator 1I-14 will appear in the transmission means I20 with an intensity envelope determined by the mesh RI32, RI33, CI30 and. Ciel. RI32 is of value in the order of 2 megohms, thus making the resistance of the pencil mark small in comparison. The cathode voltage (as well as signal amplitude) is substantially independent of the resistance of the pencil mark. The pentode I22 will act as a non-linear class C amplifier so that only the most positive portions Of the signal wave impressed upon the grid will produce a signal in plate circuit. The result will be that the output signal appearing in the transmission means I20 will vary somewhat in tone quality with amplitude, as is more fully described in the patent to Laurens Hammond, No. 2,l26, l64.

A further modified form of scanning means is shown in 41. In this embodiment of the invention the notation card is made or conducting material such as a metal sheet or a composite metal foil and paper sheet in. The sheet is connected at all times to the negative terminal of the biasing battery I I6. To make notations upon the conducting card I40, short strips I 42 of ad- 8. hesive cellulose tape, or the like, are placed upon the sheet I46 at such points at which it is desired to have a tone signal controlling relay operate. The control grid I44 of a pentode I46 is connected to a single brush !48 through grid resistor RI50. Thus the grid I44 is normally main tained at the negative biasing potential. Whenever the brush contacts one of the insulating strips I42, this circuit to the negative bias potential is broken and a positive potential is impressed upon the grid I44 through a resistor RI 52 which in this circuit is in series with RI50. RI52 will normally be of sufiiciently high value relative to RI50 that the pentode I46 will be cut oiT or substantially cut off whenever the brush I48 makes contact with the conducting notation card I40. When the brush passes over an insulating strip I42 the grid swings positive and plate current flows through winding I54 of a relay I56, the switch contacts of which may form part of the direct current control system 4I-44. Undesirable chattering at the relay I54, due to small insulation particles or dust on the conducting notation card, is prevented by the inclusion of a small condenser CI51 connected from grid to cathode.

As a further example of the manner in which the notation cards may be marked and the markings translated into a direct current, there is shown in Fig. 5 a capacity pickup system. In this system notation cards, such as the card I00, are placed upon a conducting surface provided by a metal plate I60, the markings I04 on the card being likewise made by aquadag or graphite. One terminal of a source I62 of radio frequency is connected to the metal plate I60 while the other terminal is connected to the cathode I64 of a detector pentode I66. A single brush I68, adapted to wipe past the marks I04 and to make contact therewith, is connected to the control grid of pentode I66 through a grid resistor RI'I0. This control grid is normally connected to a suitable negative potential source through a resistor RIIII and a resistor RI12 in series therewith, the cutoir potential being suflicient to maintain the pentode I66 cut off despite the presence of low amplitude RF signals picked up by the brush I 68 due to stray capacity effects. The output circuit of the pentode comprises a relay winding I14 having an RF bypass capacitor CI16 in parallel therewith. A switch I18, closed upon energization of the relay winding I14, may be in a direct current control circuit.

From the foregoing it will appear that the apparatus shown in Fig. 5 is adapted to close the relay switch I18 whenever the brush I68 is capacitatively coupled to the radio frequency source I62 due to its contact with one of the conducting marks I04, but that normally the pentode I66 is biased beyond cutoff, so that the relay I14 is deenergized and switch I18 open.

Escapement operating circuit for instrumentation sequence table The circuit shown in Fig. 6 is particularly adapted for the operation of the escapement mechanism of the instrumentation sequence table, to be described hereinafter. This circuit includes a pair of brushes I66 adapted to make contact with the markings I04 on notation cards I00 in the manner described with reference to Fig. 2 and thus change the grid bias on pentode I'80 from cutoff to a conducting value, thereby energizing winding I02 of a relay having a switch I84. The lower contact I of the switch I84 is connected to ground through a relatively. large capacitor C186 and. is connected to an operating potential'source indicated asv +300 v. through a relatively, high. value resistor RIBS. The other contact of the switch. IE4 is connected to one terminalof a solenoid winding let,- the other terminal of the solenoidbeing connected to, ground.

When the brushes make contact with a mark N34,,the relay 582 is energized to close the switch 184. It will be apparent thatthe capaci tor C186 is at all timesconnected across a suit able operating potential source through the resistor R188. Therefore, when the switch i8 3 closes, the capacitor Cl83 will discharge rapidly through the solenoid winding l st and cause the latter to operate its-plunger. This solenoidmust be relatively powerful for reasons which Will-ap pear hereinafter and, if i were not for the useof the energy storing capacitor (H86; the solenoid would impose an undueload upon any conventional vacuum tube power supply system: By providing this capacitor, however, thedrain up'on the power suppl extends over an appreciable time interval and thus the amperage of thecu'rrenttdrawn is very. low, but the energysupplied over. such a long period of time is instantly available for energiz'ation or thissolenoidwinding E90; assuring quick and powerful action-of this solenoid'.

Ifdesired, the scanning of the notation'cards andthe instrumentation--sequencecards may be accomplished by photoelectric means, as shown in Figs. land 8.

In Fig; 7 the card lilfia bearing contrasting lightintensity markings iil lis illuminated by a neon tube i94- provided with a suitable condenser lens system let. The neon tube is'energized by an alternating currentsource i96- of suitable frequency, such for example as 200 to 50010. p. s. Aphototube i98 having-a lens 'system I991 directed at the portion ofthecard illuminated by the neon tube 94; is connected across the input of a detector pentod'e 2%; Either of: the lens systems I96 and I99, especially the latter, preferably includes a suitable mask sothat each of the: phototubes I98 will respond only to'markings ona particular row of the card: I a, as the latter moves past the photo'- tube, for example, init'ne direction indicated by the arrow. Operating potential for the phototube I98 is supplied from a suitable source through a resistor RZQZ and thesignal therefrom is impressed upon the control gridot a: pentode-2ii5,through a capacitor C264 and gridv resistor R296. A potential sufficient to bias the.

pentode Zililbeyond cutoff isimpressed upomthegrid of this .pentode through azea inseries. with RZiiii. The output circuit. of the pentOde ZOt-rincludes a relay winding 210 in parallel with a high frequency by-pass condenser C212.

From the foregoing description of the apparatus shown in Fig. '7, it will appear that whenever. the phototube I98 scans a dark mark on.

the notation card iota, the intensity of the signal produced thereby will decrease suiiiciently; that the pentode 2% will be biased beyond cutofLthereby interruptingthe plate; current and; deenergizing the winding 2m of the relay, permitting its sWitchZM-to close. When,- however, the darkmark has passed the fieldof View. of; the phototube 98,- a. signal corresponding to. the

frequency of the source I93. willxbeimpressedl across the input iiltlandf will result .in .plate. ourrentflow throughthe relay windingfliiil: to open:

It will be, understood that: theits. switch; 21 4.-

Switch 214 will be in adirect' current control cir-' cuit and control the transmissionof a signal from the tone generating system to the output system or the instrument. To assure less inter ference from'outsidelight sources, the portion of the notation card 1 56a being scanned is preferably shielded bya= light shield 2-16;

Instead of utilizing the photoelectric scanning system to operate relays in the direct current control ineans the signal produced by the photo-- tubes in scanning markingsmail beus'ed directly to control the transmission of the signal from the tone generating" system to the output sys tem, as show'n'i'n Fig. 8': l'nathis figurethe means for illumination or the card and thephotoelectric pickup is substantially identical with that described with reference to Fig. '7; but the card are preferably iso'f non-reflecting blackand has white notation markings; thereon. The signal from the phototube I-QEoi Fig; 8 isimpressedupoii the grid of a pentode 222 through ablocking condenser C224. Suitable cutoff and* light thresholdv bias is impressed'- upon tl-i'e grid of the pentode 222 through a: resistor R2 -2Bi Thusas the amplitude of the output of the phot'otube 198' increases, the alternating component of the plate current of pentode 222 will correspondingly increase invalue. The output or: the pentode 222' is coupled through a. capacitor C228 with a mesh comprising arectifier cuode23cin-para1ie1 with a capacitor C232 andresistor- R234; This mesh is connected to the cathode 2 36-of arnoh=linear signal control pentode 2 38 through a' resistor R249; The musical tone signal "ge'rierated by a: source 2132: is impressed acrossthe input Dru-1e pentode 238, one terminal of the generator'beingconnectedto the gridzaaz-cr the pentode-through a decoupli'n gres-is'tor R266. An audioafre'quency by-pass capacitor GMBdsconnected in the oathode circuit while the remaining: electrodes of this pentode are connected in the usual manner to suitable sources. of operating. potential. It

willbe seenzt-hatthe outputof the p'entod 222 is rectifiedandifilteredx andimpressed upon the cathode 236, to, cause thepentode 238 toc0'nduct plate. current under: the controror the signal.impulsesuprovidedby the generator 242. The rate atv which the: cathode 2:36.15" drivennegative by the alternating: signalzprodu'ced in the output of: pentode. 2.22isac0ntr0l1'ed by the valuesoi thefiltering and delaying. capacitor C232" and re'sis tor R234; .ancl. tozsomei extent by the values of" RNB and GHB'. By-selecting these resistors and;

capacitors, of appropriate values; the amplitude of: the signal output. or the i pentode 238"- may be made to occur with any. desired predetermined tone intensity envelope uponthe'scanning of anotation mark on .the card'i228.

Notatiorn'and instrumentationsequence cards Each columnis arranged to be scannedby apa'lr' There are threerows'rof brushes W6 (Fig. 2). of notation" cards placed side by side and two! instrumentation card's placed side-by side;

The cards arepreferably made of a-duil finishmaterial which will readily take pencil marks and are of several ply thickness so they'may be durable and-ieasily'handled: The paper may be specially treated to render it less subject to shrinkage dueto changes-in humidity; and is 11 preferably tested to make sure that no parts thereof are electrically conductive.

In 14 the card is illustrated as having exemplary markings I04 thereon, the markings being indicated by cross-hatching. It will be noted that the columns 30! to 366 are arranged in rough simulation of a piano keyboard in that the Ci and D# columns are "Xd while the F#,- G# and Aii columns have parallel line. shading. This facilitates marking all the cards by the arranger or composer. In order to avoid the necessity that the composer or arranger completely fill in the block markings I04, he may merely draw a line parallel to and within the column and an assistant may thereafter fill in a complete marking represented by the crosshatching in Fig. 14.

As illustrative of the character and scope of the instrumentation available, the character of the operations controlled by the various columns of the notation and instrumentation cards which have been found practical, will be set forth.

Of the first notation card, columns 30! to 34! will be used to determine which of the notes C2 130.81 c. p. s.) to E5 (1318.51 0. p. s.) of generating system I are to be sounded. Columns 342 to 353 of the first card will be used to determine which of the notes F (43.654 0. p. s.) to E! (82.407 0. p. s.) of the bass generating system II shall be sounded. Column 354 will be marked when any note of generating system I is required to be weakly accented. Columns 355 and 356 will be marked to cause strong accents on tones of generating system I, and medium accents on the tones produced by the generating system II, respectively.

Of thesecond notation card, columns 30! to 34! will be marked to determine which of the notes C2 (130.81 0. p. s.) to E (1318.51 c. p. s.) of the generator system III shall be sounded. Columns 342 and 343 will respectively cause weak and strong accents of the tones of generator system III. Columns 344 to 356 will respectively control notes G2 (196.0 0. p. s.) to G3 (392.0 c. p. s.) of the accompaniment generator IV.

Columns to 34! of the third notation card will be used respectively to control notes C2 (130.81 0. p. s.) to E5 (1318.51 0. p. s.) of a generating system V. Column 342 is used to control medium accents on the notes of accompaniment generator IV, while columns 343 and 344 are utilized respectively to control weak and strong accents on generating systems V. Columns 345 and 346 of the third card are used respectively to cause rapid and slow deceleration of th motor driving carriage to produce decelerando eifects. Similarly, columns 341 and 34B are used to produce slow and rapid accelerando effects. Marks in columns 349 to are utilized to produce various degrees of decrescendo effects, while marks in columns 352 and 354 are utilized to provid various degrees of crescendo effects. Marks in column 355 produce drum effects. A mark in column 356 will produce an orchestration shift, that is, a change in the instrumentation sequence table so as to effect any desired change in the overall instrumentation employed.

The first instrumentation card utilizes a mark in columns 30! to 304 to control the output volume of generating system I. are used to determine th register of generating system I. Columns 309 to 3!3 are utilized to select the tone quality of generating system I. Column 3!4 is used to mute the tones of generating system I, while column 3l5 is used to,

Columns 305 to 308 1 cent table.

determine whether the tones of generating sys tem I shall have vibrato. Columns 3!! to 325 control the percussion branch of generating system I, columns 3!! to 320 determining the degree of volume, while columns 32! to 325 select any on of five tone qualities for the percussion branch of generating system I.

Columns 328 to 33! are used to select any one of four degrees of volume for bass generating system II, columns 332 to 334 selecting any one of three registers for this generating system, and columns 335 to 339 selecting the tone quality of the bass generating system I. Columns 342 to 354 control the operation of generating system III, the first four columns determining the volume, the next three the register, the next five the tone quality and column 354 controlling the vibrato.

On the second instrumentation card, marks in columns 30! to M0 control the output of the accompaniment generator IV, the first four columns controlling four different degrees of volume, the next five columns five different tone qualities, and the tenth column the vibrato. Columns 3I3 to 323 are for the control of generating system V, the first four columns of this group controlling different degrees of volume, the next five different tone qualities, while the last two respectively control the mute and the vibrato. Marks in columns 325 to 333 control the output of the percussion branch of generating system V, the first four controlling different degrees of volume, while the remainder control different tone qualities. Columns 336 to 346 control the drum section, the first four columns determining different degrees of volume, the next five different tone qualities, and the last two determining different tone intensit envelopes.

In the center of each card there are numbers 0 to 9 imprinted in alignment with transverse lines 360. The distance between these lines will normally represent the time interval of a quarter note, thus four times this distance between the lines 360 will represent a measure in 4/4 time. Intermediate the lines 360 there are dash lines 362 dividing the quarter tone interval into eighth tone intervals. There are also light lines 364 dividing each quarter tone interval into three equal parts for the scoring of triplets.

The notation card table As shown in Figs. 9, l0 and 11, the notation card table is built up in sections, the first section 366 being constructed in the manner of a conventional table with four legs 36". The remaining table sections 368 are provided with only two legs, both at one end of the table section, the other end of the table resting upon brackets 310 projecting from the adjacent legs of the adja- Suitable shims 312 are provided so as to make the tables 368 level with one another.

A pair of tracks 314, preferably of inverted T-' section, are secured to the tables by suitable brackets 376 and successive sections thereof are bolted together by suitable fish plates 318. By virtue of this arrangement, the tables may quickly and easily be assembled with the tracks smooth and level.

The locating pins for positioning the notation cards upon the tables are preferably of the construction shown in Fig. 11. From this figure it will be seen that each of the pins is mounted in the table top 31'! projecting through an enlarged hole 380 formed in the top. Each pin 382 has a reduced diameter rounded end portion 384 for engagement in the.- perforations of. the cardS,. and has. a washer 385rwelded thereto. The lower end of; the. pin. is. threaded for a clamping nut 3.88 which bears against; awashei: 389, aqsuitable lock washerc'sil'being. utilized. The washers 3-86 and 389 are of .suihciently great diameter that. upon loosening. the nut 388., the pin .3.82. may be moved in. any direction within the. limits of the hole 384;. thereby facilitating accurate. location of the ends 384 of the pins. in the table? with. the tolerances customary in woodworking: practice and after the rails 314 have been secured to the tables and all of the tables are assembled, the ends 334: or the: pins may be accurately located with. reference. to: the pins in: adjacent tables so that. their. spacing may he accurate to a high degree of precision.

The scanning carriage The'scanning carriage, designated generally by the reference character 2W2, is mounted upon V- grooved or flanged wheels 393 resting on the tracks 314- and is driven by a motor 394- through a suitable speed reducing gearing which is enclosed in the motor housing. Suitably mounted on the carriage are 168' pairs of brushes Hlwhich project downwardly a-t'an angle so as. to resiliently contact the three cards placed side by side uponthe surface of the table. Most of the elements of the circuit shown in Fig. 2, such as the pentodes H2 and circuit elements EH4, RH5- and RI l8 and Cl H, are alsocarried by thecarriage.

The conductors i i-9 from the fifty-six pen-todes H2, as well as conductors supplying operating potential for these pen-todes are bound in a flexible cable 396 leading" to the other components of the apparatus.

The instrumentation sequence table The instrumentation sequence table is shown in Figs. 12 and 13 as comprising a base4'0ll having a pair of V-grooved rails 4E2 mounted thereon for the reception of ball. bearings 40.4. A movable table 406 has corresponding grooved rails 408 which rest upon the balls. 454,, thus providing an anti-friction support for longitudnial movement of the table 496- relati-ve to the base 400. Suitable locating and aligning pins 382-, 384 are provided for properly positioning a pair of cards I00 (Fig.14) upon the table 496.

Along the center of the table are tworows of staggered upwardly projecting pins M0 for cooperation with an escapement pawl 412 which is suitably pivoted on a cross frame 414 and operated by a solenoid I98. The table 406 is drawn rearwardly by a long tension spring 4i8 which has its end respectively anchored to the base 400 and a pin 420 projecting downwardly from the table 406. The cross frame 414 is guided for vertical movement in a. pair of grooved posts 422 projecting upwardly from the base 400. The cross frame carries two banks of contact brushes I06, there being 56 pairs of contact brushes H16 in each bank. These contact brushes cooperate with the markings on the cardsv lflil to complete circuits and cause energization of relays in a manner such as disclosed in Figs. 2, 4 or 5.

Thus when there is a conducting mark in column 356 of the third notation card, the contact brushes I06 making contact therewith will render the tube I83 (Fig. 6) conducting, energizing the plate circuit relay I82, I84 and permitting the charge stored in the capacitor (N86 to energize the solenoid. I90. Whenever the solenoid 1-90 The holes380. may be drilled through resistors R443, R449 and R450.

signals of the various generating systems.

The system as a whole is preferably rendered more flexible in use by providing means whereby the connections of the conductors us (Fig. 2) maybe selectively coupled to any of the various control means. In this way there may be as many tone generatingsystems as desired and only those selected for the rendition of a particular composition may be coupled to the instrumentation sequence scanner.

Expression control and volume system The expression control indicated by the block 56 in Fig. 1' and the volume control systems represented by the blocks 9i to 9:2 of Fig". l are preferably of the nature shown in Fig. 15.

In the latter figure the output systems of seven generators are diagrammatically illustrated, these output systems corresponding to the outputs of the'tone quality systems 8i to 34 of Fig. 1', each being illustrated as being coupled by a transformer having a secondary winding 436) to the input of a preamplifier tricde 432 through meshes comprising resistors R433 to R438 in series and shunt resistors R439 and R440. Each of the resistances R433 to R43! is shunted by a switch 44'! operated by a relay 449a, these relays being operated by the scanning brushes use when they contact appropriate markings on the notation cards of the time sequence scanning system.

The resistors R433 and R435 are of properly graded values so that upon energization of the relays associated with resistors R433 and R434 difierent degrees of accent will be produced by changing the impedance of the mesh, which includes these resistors, for the particular generating system upon which the accented note is desired. Likewise the resistors R435, R436 and R431 are preferably of such values that upon successive operation of the relays 45m associated therewith the volume may be increased and decreased logarithmically. The shunt resistors R440 of the various outputs of the generating systems are connected in series between ground and the decoupling resistor R4558 so as to mix the signals of the various generating systems.

' The amplitude of the combined signal of all the generating systems has its amplitude controlled by decrescendo relays 44th, 542 and 4-43 and crescendo relays 444, 445 and 4%. The relays 441* to 443- upon energization are adapted to connect the control grid of the preamplifier tri ode 432 to a grounded conductor 4 3? respectively These resistors are of graded values so that upon successively energizing the relays 443, 442 and 44lb the amplitude of the combined signal appearing on the grid 432 will be decreased in logarithmic steps. On the other hand, the energization of the relays 444, 445- and 4 16 will result in opening circuits through resistors R455, R452 and R453 so as. successively and in a logarithmic manner increase the effective resistance between the grid. of triode. 4,32. and the grounded conductor 441. In this manner overall crescendo and decrescendo eifects may readily be obtained by appropriate markings in the six columns or the notation card.

The output of the preamplifier triode 432 is coupled to a power amplifier 454 (forming part of the output system 95-Fig. 1) and supplied to the monitoring speaker 91, or the recorder 96, or both.

Octave coupler system As shown in Fig. it, suitable controls are preferably provided in the apparatus for effecting octave coupling so that by the provision of a single mark upon the notation card the output signals of a number of octavely related generators of a particular system may be simultaneously coupled to the output of the apparatus as a whole. in Fig. 16 there are five pairs of scanning contact brushes 106 which are representative of the brushes cooperable with two or three octaves of markings for a particular generating system. Each pair of brushes operates through a pentode such as H2 (Fig. 1) to control a relay, these relays bearin the reference characters 468, 46!, 462, 463 and 464 respectively. These relays, upon energization, are adapted to connect a source of suitable operating potential, indicated as +210 v., to bus conductors 416, 41!, 412, 413 and 414 respectively. A plurality of octave coupler control relays 415, 416, 411 and 418 (Fig. 16) are adapted to be energized by appropriate markings upon the instrumentation sequence cards, and respectively control the addition of the second octave, the octave, the unison, and the suboctave. Each of the relays 415 to 418 has a plurality of switches 419, one associated with each of the bus conductors 416 to 414, so as to connect the latter through a high value decoupling resistor R488 to the input or" one of the plurality of suitably biased rectifier pentodes tit-2. Connections between the resistors and the rectifier tubes 482 are such that when the relay 411 s energized and a relay such as 4th is energized, only the note represented by the marking which has resulted by the energization of relay 466 will be sounded, whereas if in addition the relay 416 is energized, the note and its octave will be sounded, since in this case the bus ile will be connected through two decouplin resistors R489 to different rectifier pentodes 482 as will hereinafter appear. This will result in sounding of the note and its octave.

Each of the rectifier pentodes 462 has a relay 484 in its output circuit, this relay being adapted upon energization to connect a suitable potential shown as l35 v. to the cathode of a control pentode 480 through a circuit identical with that shown in 3 and operating in the same manner to cause the transmission of a signal from a tone generator 1 [-14 to its output system represented by a signal collector conductor 488.

Since in Fig. 16 only a representative portion of a complete octave coupler system is disclosed, the generators 'ii Hi will generate octavely related frequencies such as those of the notes Ci to C6, While the relays 4613 to 26 5 Will be respectively associated with the contact brushes 106 of the card columns representing octavely re lated notes C2 to C6.

The resistors R463 are of high value relative to the input impedances of the pentodes 42. Thus when two or more of the relays 415 to 418 are energized at the same time, no spurious circuits can be completed because the resistors R488, being of high value (with respect to the grid-to -cathode resistance when the grid is drawing current) prevent substantial current fiow in a reverse direction. For example, if the relays 411 and 418 were energized and the note controlling relay 460 onergized the first and second pentodes 482 (from the top) would have an operating potential impressed upon their grids, suihcient to cause grid current flow and thus to reduce their input resistances from infinity to a value low in comparison with R486. Thus, this enormous drop in input impedance prohibits a substantial current .to flow from the grid conductor of the second pentode 482 through its associated resistor R480 to the conductor 41!. It will be apparent that if there were any appreciable flow through said last named resistor R486 to the conductor 4, current might also flow to the grid of the third pentode and energize the latter. However, as each of the pentodes 482 is rendered conducting and at very low input impedance by impressing the high grid voltage (+216 v.) on its grid circuit through R486, there is sufiicient grid-to-cathode current flow in the pentode so that the actual potential of the grid is very low and, therefore, there cannot be a sufiicient potential buildup upon grids of other pentodes 42 through the previously described spurious paths to cause the latter to conduct current.

In Fig. 16 it is assumed that the generator system is of limited gamut, extending through the note C5 but not extending to the note C1. As a compromise result, the switches connected to bus conductor 414 and associated with the relays 415, 416 and 411 and the resistors R480 connected thereto are in parallel and connected to control he generator for the note C6.

The generating system employed with the octave coupler control system of Fig. 16 is preferably of the type shown in the patents to L. Hammond Nos. 2,126,464 and,2,126,682. It will be noted that the method of signal amplitude control which includes the pentode 486 of Fig. 16 is similar in principle to that disclosed in said Patent No. 2,126,464.

Xylophone tone signal generating system It is nearly a practical necessity for the artistic rendition of orchestral music that percussive tones be employed to provide contrast to the sustained tones and, therefore, means for producing percussive tones of the Xylophone type, as shown in Fig. 17, is provided. In Fig. 17 contact brushes I 06 are adapted, through the pentode l I 2, to control the operation of a relay 490, which upon energization connects a negative potential source, indicated as v., through a mesh, comprising resistors R491, R492, R493 and R494, to a terminal 495 of the tone quality system 84. The resistor R492 has a capacitor C496 in parallel therewith and the junction between the resistors R493 and R494 isconnected to ground through a resonant mesh comprising an inductance L491 and a capacitor C498. A control pentode 499, which corresponds to one of the pentodes 486 (Fig. 16) is adapted to control the output of a suitable signal generator 11-14, the output of the pentode 499 being suitably coupled to a tone quality system 8l94. The terminal 495 represents a common terminal for a plurality of the meshes R45 to R494, C496, C498 and L491 associated with other relays similar to relay 490.

The frequency generated by the particular tone generator 1|14 associated with the pentode 489 is preferably the same as'that at which the mesh L491, C498 is resonant. Upon energization of 17 "the-relay-MB thetransient-produced upon; closure its 1 switch 7 is transmitted to the terminal "495 through the intervening mesh, but only suchifr quencies as correspond rather closely to 'frequencies of the generator II-M will be trans-- mitted to the outputsystem. The resonant mesh L491, C498 *does not have a su-fliciently high Q to exclude lrequencies'difieringby'as muchzas a semitone or morefrom the output and therefore this signal is heard as a percussive musical-tone of recognizable -but=not'--a-solearly-"define'd -in pitch as the usual sustained type of tone.

Upon closure of the switch of relay 4 53 the negative 135 v. potentialis impressed uponthe cathodeof the pentede 49-9, through t'he resistor R49! and additional attack resistor RS'iiEl, ata rate determined inpart loy capacitor C591; there- "by rendering the-pentode 499 conductive-"of't-he signal supplied'by the generator 'll-74. After 'deenergization of the =re'lay 450; cathode current is still supplied to theepentode 499 from thecapacitor 0501, so that the tone willdecay at a :gr-adual rate determined by the relative values-or R550 and C595. 'Thus upon energization-of'the relay A9 0 a: signal :constitu-ting l both apercussiwtone and asustained tone ('thelatter beingproducedbythe-generator' 'lk lfl of rapid attack and slightly -slower decay, will be produced in :the :output -system. This tone -.-will be respective- :lynf thexylophone and brass types and-will iuseful inimany orchestral renditions.

Generator system jjQTi'fIMTQZLSSiUfi piano-like tones -In"Fig. l8th'ere"is"illustrated acircuit suitable for the control of the tone envelope of a.gen- J ierator system iprcducing sustain-ed tones, under 'theco-ntrol'of "conducting 'markings on a'notation card. In this circuit contact "brushes I do, upon passing 'over "a conducting mark on the card. change the grid f-bias of a'pentode 582 from negative-value beyond "cutoitto a positive value in a manner similar to that previously described with reference to Fig. 3. ;In :Fig. 18, however, the pentode B2 operates as an impedance changer 'so that thevalue o fthe resistanceiinposed by the markingjon'the card across the 'brush'eslllfi is notof controlling character. This is"bec,ause"th'e peritode 5'62 decouples the card 'mark and "cable impedances from the. remainder of the circuitwhi'chis of high impedance -would be susceptible to spurious leakage, etc. The anode 'ofthefperitode "502 is supplied from "a :suitable source 'ofiplatevoltajgethrough aresistor'R5fl4 in parallel with a capacitor 105%. The anode of the .pentode 202 is also connected to the cathode "5118 of a control .pentoide 5E0 through a resistance 'R5l2. The .pentode h! has a sharp peak wave impressed thereon ,by a generator 'H-l4 and the output of the pentode is suitablycouple'd 'toa signal collector conduc- .tor .514 throug'ha capacitor C515 and a decouplingresistor R5l8. The anodes of a, ,p1uraiity ofjpentodes Slilmay'beconnected to thecollector conductor 5 M through the same, capacitor C5 i ii and resistor R518.

When the contact brushes I96 pass over a control marking onfa notation card, the ,pentode 502' is rendered conducting so that .the potential of "its plate drops at a rate determined by the tube characteristicsand the values of'CEBG, and "R584. This drop in platepotential'is reflected on the cathodefi'UB of the .pentoder5llland therefore renders thejlatter conductive of the signal impressed upon itsinput circuit. 'It will-"he noted that the plate of pentode "502 is normally at a 53 9 and 53 thereof through --'a timeconstant capacitor G532 and resistor R534. --Pla-te potential "is provided jpotential or? volts above that ofthefcathodetilti dueto the provision of abatteryfi Hi. This latter 'potentialnormally completely cuts'off plate. cur- "rent in tube 5 i=0.

The circuit of Fig. 18 is of advantage'oversome of the previously described control circuits in that no electromagnetic relay is required.

Apparatus "for producing-drum signals An important elementof orchestral music,-.par-

ticularly that .of popular nature, is imparted by the percussion beat -of drums. I have therefore provided :a means for electronically producing electrical signals corresponding to the beats-Inf drums. Such .an apparatus? is .shown in Fig. (19

as comprising the random .frequency generator 520. This generator may be any suitable source of random noise -such,- for examplewa signal picked up from the phonograph record of the noise of waves --breaking L 'on a beach, but is-preferably an The output of i the random frequency generator 526 is connectedto'the-primary of a transformer pr-ising resi-stor-s R524, R525 in series and a shunt mes-h comprising R526 and G521. *Aflo'ad resistor R528 is connected in parallel with-"the primary W-indingof a transformer 522. These'c- "ondaryof the transformer 522 has a center 'tap connected to a 'suitable biasing -.potential--souree indicated as-a 7 terminal :7 v.- and has its terminzils-connec-tedto the grids'of apair of 'push-pull pentodesES-ll, 531. The screens of the pentodes are connected to the cathodes "from a source indicated as a +300 v. terminal through load-resistors R536 and R531 as wellas through the center tap primary "of "an output transformer The-screen grids of the pento'des 53!) and 53 I are nor-mally 'maintainei'l "at ground "or cathode --potential 'loy virtue of th'e'ir connection to the cathodes'ofthese-tubes-by-the resistor-R534. When the contact brushes to'ii' for 546 is energized to'connect the screen -grids 0f the pentOdes-"SBQJESI to a suitable source-0'1 operating potential shown-as a +100 v. terminal,

this .connection being effected through a-nattack resistor RMB. Two -.or more capacitors C543,

ground. upon closure of switches 545, 5616- respectively. When both switches 555 and 5 19319 open,

the screen gridsof the pentodes 53i), *53l-will be rapidly-raised to operating potential when "the relay 5% is "energizedgandthus produce a percussion tone with a very sharp attack. Wnen=-' it is desired to lessen the sharpness of this attack and to prolongthe'decay period-orthe percussion ,drum tone, either switch.545, or switch r546 or both, will be closed, (thereby slowing up the rate 'pled to one of'tone quality systems '8! to 8'4, and

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