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Mode of Operation of the Pentode Or Tetrode Tube in the Output Stage Of Web: http://www.pearl-hifi.com 86008, 2106 33 Ave. SW, Calgary, AB; CAN T2T 1Z6 E-mail: [email protected] Ph: +.1.403.244.4434 Fx: +.1.403.245.4456 Inc. Perkins Electro-Acoustic Research Lab, Inc. ❦ Engineering and Intuition Serving the Soul of Music Please note that the links in the PEARL logotype above are “live” and can be used to direct your web browser to our site or to open an e-mail message window addressed to ourselves. To view our item listings on eBay, click here. To see the feedback we have left for our customers, click here. This document has been prepared as a public service . Any and all trademarks and logotypes used herein are the property of their owners. It is our intent to provide this document in accordance with the stipulations with respect to “fair use” as delineated in Copyrights - Chapter 1: Subject Matter and Scope of Copyright; Sec. 107. Limitations on exclusive rights: Fair Use. Public access to copy of this document is provided on the website of Cornell Law School at http://www4.law.cornell.edu/uscode/17/107.html and is here reproduced below: Sec. 107. - Limitations on exclusive rights: Fair Use Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, includ- ing such use by reproduction in copies or phono records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for class- room use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include: 1 - the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; 2 - the nature of the copyrighted work; 3 - the amount and substantiality of the portion used in relation to the copy- righted work as a whole; and 4 - the effect of the use upon the potential market for or value of the copy- righted work. The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors ♦ PDF Cover Page ♦ ♦ Verso Filler Page ♦ United States Patent Office 3,153,766 Patented Oct. 20, 1964 1 2 privilege of the amplifier designer. The positions 3,153,766 chosen will determine the two different sets of MODE OF OPERATION OF THE PENTODE OR. characteristics between which the power output TETRODE THE OUTPUT STAGE OF TUBE IN tube will alternately operate. AUDIO POWER AMPLIFIER AN Renato E. Tancinco, Meycauayan, Bulacan, Philippines 5 Filed Sept. 8, 1961, Ser. No. 136,817 The New Circuit Claims priority, application Philippines Sept. 12, A good amplifier must not only be good in perform­ 1%0 Claims. (Cl. 330-1'22) ance but it must meet the require ents of the manu­ 5 m facturer, the amplifier designer, and above all satisfy the This invention relates to a new concept in the mode 10 ultimate user, i.e., the owner. of operation of a pentode or tetrode power tube in the It is a fact that in the reproduction of music, the output stage of an audio frequency amplifier. Up to high power peaks are relatively few and of very short the present stage of the art, the output tubes in an audio durations, that, most of the the amplifier may be time frequency amplifier operate only of char­ under one set considered as idling. Low consumption of power dur- acteristics which is determined by the mode of opera­ ing idling is therefore of paramount importance. An 15 tion assigned to them. The following are the modes of amplifier is usually rated at the maximum power that it operations under w ich a pentode or tetrode power tube h can deliver during these peaks, with a minimum of dis­ may be made to operate : tortion and good stability. The maximum power that (1) Triode connected pentode or tetrode output stage. a pair of power tubes can deliver is usually limited by i of (2) Distributed load pentode or tetrode output stage or 20 the maximum plate dissipation rat ng the said power the so called "Uutra Linear Amplifiers." tube. To get therefore the most out of a pair of power (3) Straight pentode or tetrode output stage. tubes, the plate circuit efficiency of output stage should (4) Unity coupled output stage. be high. It is also very desirable to obtain high power (5) " xtended Class Amplifier" using a pair of triode outputs without the necessity of using very high signal E A connected push pull pentode or tetrode paral el grid drive voltages. In other words, the power sensi­ in l 25 with another pair of the same type of tubes con­ tivity of the output stage must be high. It is therefore nected as straight pentode or tetrode. clear that Class B operated pentode or tetrode power tubes appear to ideal for the output stage. The re­ The sixth mode of operation is offered by the under­ be quiremen of low distortion in ou put stages using the signed and is the subject of this patent application. t t In conventional Class pentode or tetrode power tubes is, this new modc of operation, the output pentode or 30 B however, not easily met. The cause is the presence of tetrode tube alternately operates between the two sets a form of distortion, called the notch distortion, which of characteristics assigned to them. These two sets of occurs as a notch or fuzziness in the output signal wave- characteristics are determined by the position of he two t form. In reality, this fuzziness in the signal taps on the plate winding of the output transformer to 35 output waveform is a form of shock excited self oscillation at which the anodes of the back to back connected diodes, some ultra-sonic frequency in plate winding of the feeding the screen grid of the said power tube, are con­ the output transformer. The leakage inductance between nected. The particular set of characteristics under which the plate windings of the output transformer forms an the output tube operates is determined by the polarity oscillatory circuit in combination winding of the grid signal voltage relative to the quiescent poten­ 40 with the capacitance and other stray capacitances. This oscil­ tial of the control grid, otherwise known as grid bias. the latory circuit is shock excited into self-oscillation every Some of the objectives of this invention are as follows: time the plate current of the power tube is driven to (1) To obtain high quality reproduction of sound with- cut off. Unfortunately the frequency of this fuzziness or notch distortion is so high that is beyond the effec­ out the necessity of using expensive special output 45 it transformers or resorting o o pl itr . control of the inverse feedback loop that may be t c m ex circu y tive (2) To be able to obtain the most power output avail­ applied in the amplifier. Furthermore, the plate cur­ able for a given power output tube and a given B­ rent of the power tube which is the most logical part supply voltage, commensurate with high plate circuit �f the amplifier that can prevent the said distortion, has efficiency, low distortion, and low power consump­ been driven to cut off. The said power tube, being then 50 tion during the absence of signal or during idling. inactive, is therefore not in a position to prevent the (3) To att the above objectives without the neces­ occurrence of the said notch distortion. So far there ain sity of using more than one pair of power output tubes are two successful solutions to the problem of prevent­ or more than one power supply or B-SuppJy. ing the occurrence of the notch distortion. They are exemplified in the Unity Coupled mplifiers and the (4) To reduce the output impedance of the power out­ 55 A put stage before the application of any inverse feed­ Extended Class amplifiers. A third solution is offered A back. by this invention, which is believed to be an entirely (5) To be able to attain the above objectives without new concept in the mode of operation of pentode or the need for very high signal grid drive voltage to the tetrode power tubes in the output stage of an audio power power output tubes. amplifier. 60 (6) To give the amplifier designer a free hand in the The foregoing objectives will become more apparent design of the whole amplifier. The said freedom is from the following detailed description of various em­ achieved by virute of the following: bodiments of the invention and from the accompanying (a) Absence of inherent inverse feedback in the drawings wherein: output stage. The manner of application of the FIG. 1 is an electrical schematic diagram illustrating 65 inverse feedback is left entirely to the amplifier a push -pull tetrode power amplifier incorporating the designer. switching diodes in circuit between the screen grids and (b) The designer is free to choose any type of output transformer. pentode or tetrode power tube for the power FIGS. 2-4 are views similar to FIG. 1 but illustrating amplifier stage. various modifications for connecting in the switching 70 (c) The choice of the position of the taps on the diodes; and plate winding of the output transformer is FIG. is a detail of one of the switching diodes in- the 5 3,153,766 3 4 dicating the convention observed in designating its cath­ former T-2 can be any standard output transformer ode and anode components.
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