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22 Tested Circuits Using Micro Alloy Transistors

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22 Tested Circuits Using Micro Alloy Transistors ~No . · 181' 22 TESTED CIRCUITS USING MICRO ALLOY . ';;, TRANSIST-ORS " fly Clive Sintlair I .... All circuits have be•n tasted by a panel of amateur constnictors,. ' w •• Complete parts bsts and ftlb constructional detal•· 26 comprehensive theoretk- dlagrama. Practkal hints and tips on constn1ctlon. Super ••n•ftlv• receivers# transmitters, and ampllflers fuUy de•crlbe4.. Comprehen•lv• serYlclrlg data Included. ·~· . Fe1ult finding and p-:attft:at ~ bints and tips ;#<. • for tile constl'UCtCJr: - ~ •.' I I ' I . ' • ' ( I • • I• \ • . I :,v • • " BERNARDS. (PUBLISHERS) LTD. THE GRAMPIANS WESTERN GATE LONDON, W.6 'l. • Fl RST PU Bl_JSHED J ,>\ N ll A I~ Y. I t)(l_; REPRINTED SEPTEMBER, 1964 • ,1. •• We invite all authors, whether new or \\'ell established, to submit manuscripts for publi,catiDn. ·The manuscliipts may deal with any facet o.f electronics but should a1ways be practical. An.y crrc.tiit diagrams that may. be · inclu.ded should have been thoroughly checked by ·the author. If you ! are considering tr.ying your hand at writing this. typ~ of book we suggest that you Jet us have a short sumn'Wlry of the subject you intend to cover. We will then ,: ab1e to let you know the size of ' book required and J)erhaps give you some .a r ,. ice on the presentation.. © 1963 Printed by. The Wintworth Press Ltd., 25 Prince· George Street. Portsmouth. Hants, for Bernards (Publishers) Ltd., The Grampians, \ 11estern Gate, London, W.;6 . • - - ---- - -·- - ··" . ' CONTENTS c: 11a ptcr J. An introduction to the MAT • • • • •• • • • • • • • • • • • MAT specifications • • • • • • • •• • • • • • • • • • • • • • • • .6 Encapsulation and 1ead connections· • • • • • • • • • • • • • • • .7 Chapter 2. Circuit techniques v;ith Micro Allo}· 'l"ransistors • • • • • • •• • 8 ' Amplifier circuits • • • • • • • • • • •• • • • • • ••• • • • .8 OscilJato.r ci.rcuits • • • • • • • • • • • • • • • • • • • • •• • • • 9 Frequency changers .. ... • • • • • • • • • • • • . .... • • • 9 R.F. and 1·.F. Amplifiers • • • • • • . ' . • •• ... , ... -... I 1 Reflex Amplifiers • • • • • • . .. .- • • • • • • .. , • •• • • • I I ..• :Detectors and Regenera ti v: · detectors • • • • • • • • • • • • • • • 12 .. • . ~ .. I • Chapter 3. Practical MAT circuits • • • • • • • ••• • • • • • • • • • • • • 15 • Very high gain 25 mW amplifier • • • • • • • • • • • • • • • ••• 16 • Three very low noise pre~ampl ifiers · • • • • • • • • • • •• • •• 16 Sing1e transistor phase shift oscillator • • • • • • • • ••• • • • 18 Two reflex ·receivers ... • • • • • • • • • • • • • • • • •• • • • 18 Regenerative • receivers • • • •. • • • • • •• • • • • • • • • • • 20 ·short wave transmitter. • • • • • • • • • • • • • • • ••• ••• 22 Synchronous detector F.M. tuner • • • • • • • • • • • • • • • • • • 24 FM I VHF transmitter • • • . • • • • • • • • • ••• • • • 24 Sttb-miniature radio control receiver • • • • • • • • • . •.. • •• 26 Superhct receivers using MAT's · ... • • • • • • - .. • • • • • • 26 • ·, .. • .. • ·'i • I J. I 'i I ' i .I Ll.. ~T Of. 11.JLU~TRATIONS . I ). Pttf!(' 1 ' .' I . .I Fig. ·1 Practical dimensions and pin connections of MAT's • • • ••• • •• 10 Fig. 2 Example of direct... couplcd A.F. amplifier • • • • • • • • • • • • • •• 10 . • Fig. 3 Basic circuit of a phase shift oscillator .. • • • • • • • • • • • • • • • 10 Fig. 4 Example of reflex. receiver • • • • • • • • • • • • • •• • • • • • • 10 Fig. 5 Improved reflex circuit • • • • • • • • • • • • • •• • • • • • • • • • 13 Fig. 6 Typical transistor de·tector circuit • • • ••• • • • • • • • • • • • • 15 . •'-·: Fig. 7 H~gh performance regenerative detector circuit • • • • • • • • • • • 15 Fig. 8 High stability t mW direct-coupled amplifier ... • • • • • • • • • • • • 15 Fig. 9 Very high gain 35 in\\' amplifier ... • • • • • • • • • • • • • • • • • • 17 Fig. l Oa Low noise low impedance pre... amplifier • • • • • • • • • • • • • • • 17 • Fig. 10b Low noise medium impedance pre·amplifier • • • • • • • • • • • • • • • 17 Fig. 1Oc Low noise high impedance pre·amplifier • • • • • • • • • • • • • • • 17 ! ; . Fig. 11 1 Kc Is·phase shift oscillator • • • ' • • • • •• • • • •• • • • • • • • • 19 f. 19 Fig. 12 Sensitive low cost reflex receiver t ... • • • • • • • • • • • • ••• • r ..... Fig~ 13 Loudspeaker reflex receiver • • • • •• .. , . • • • • • • • • • • • • 20 • • • • Fig. 14 2-transistor super regenerative receiver ... • • • • • • • • • • • • 21 Fig. 15 · High performance ·very low voltage · ·regenerative receiver • • • • • • • • • 21 Fig. 16 Short wave receiver for all bands wit.h regcncr3tive receiver ... • • • • • • 22 ,'' ' . Fig. 17 Short wave transmitt.er • • • • • • •• • • • • • • • • • • • • • • • • i r Fig. 18 FM tuner with synchronou·s detector • • • • • • • • • • • • • • • • • . 'I Fig. 19 FM / VHF transmitter • • • • •• • • • • • • • • • •• • • • • • • .,~ • . Fig. 20 Sub-miniature radio control recei\'·er with half-mi1e ra11ge • • • • • • • • • -- l t· .' Fig. 21 High sensitivity 3-transistor pocket superhet • • • • • • • • • • •• • • • 27 I I J Fig. 22 Loudspeaker amplifier • • • • • • • •• • • • • • • • • • • • • • • • 27 .! • \. Fig. 23 Sub-miniature 3-transistor Joudspeaker superhet • • • • • • • • • • • • 2~ • ' j' . • • ·, ~· .. ------·..... · .. .. ........ _________. -· 22 TESTED CIRCUITS USING MICRO .~lLOY TRANSISTORS . • • • . ~· An Introduction to the M.A.T . - Since the initial invention of the point con­ collec·tor current and voltage but is a poor R.F. l tact transitor some twelve years ago engineers . amplifier by comp~riSOll. The alloy diffused have continually striven to develop new types type is an excellent R.F. ·transistor 'Yhich c~.n with improved performa11ce. The original point operate right ·up to V.H.F. frequencies but ts contact transistors were very noisy, rather deli­ not very good as an A.F.. amplifier or .at low cate and it was very di.fficult to produce con­ collector currents and voltages. A transistor sistently good quality ty·pes. When the alloy was required.. therefore, which combined and j.unction transistor was . invented, therefore., they extended the advantages of both types just men­ rapidly became obsolete. Alloy junction tran­ tioned without any. of ·the disadvantages. An sistors, such as the OC7 l and O.C44, 1nake early attempt to achieve this resulted in the.sur­ excellent A.F. amplifiers with comparatixely f ace barrier transistor or SBT. The SBT was Jow noise figure~ and R.F. types may be use 'at m~de . by ~lectrochemically etching a\\·ay tlte f1·equencies of up to about 5Mc Is. Even at ... e­ base· prior .. to plating on the col.lector and di un1 wave band frequencies· of around !Mc.ls, emitter electrodes. This . resulted in an ex­ l1owever, their gain .is comparatively low tje.. tremely narrow· base width and, hence. a very cause even the, best of them provide a common high cut-off frequency. SBT's operated perfectly en1itter current of only ~tbqut 10 times at these at both audio and radio ·frequencies and they frequencies. could .also operate at · very low power levels. To o·verconie. the limitations of the conven­ Unfortunately, however, their common emitter tional alloy transistor the alloy diffused ·type current gain was always very low and they were was developed, examples of this type being the limited to collector currents of 5mA and col­ OC l 70 an~ OC 171. In these the resistivity of the lector voltages of 5 volts. These disadvantages t base region, instead of being;,. constant, varies precluded their wiqespread application although steadily from the emitter to the collector.. This they were very useful for some purposes such results in the charge carriers being accelerated as in radio control receivers. or in radio receivers · across the. base thus reducing the transit time designed ·to operate from low voltage batteries. an~ increasing ·the cut-off frequency. Alloy Finally the .·micro alloy transistor, or MAT, diffused transistors make excellent, high gain was developed. rhese are made by a technique R.f... amplifi.ers at M.W. frequencies a11d they similar to that.·invented for SBT's but developed will operate up to lOOMc/s or more. However, considerably to overcome all the disadvantages they have very high saturation· voltages 'which . of the latter. MA'"f's have extremely high levels means that a. C·omparatively high collector vol­ ·of current gain, as high as 200 in many cases, tage must be used and their current gain drops and they can also operate at collector currents rapidly as the collector current is reduced of up t<) 50mA and collector voltages. up to · making them unsuitable for operation at low about 12 volt5. Their cutoff frequencies are as collector current levels. They also tn~ke poor high or higher than those of alloy diffused tran­ A.F. amplifiers. and are thus difficult to use in sistors and yet they make better A.F. amplifiers reflex circuits unless the designer takes numer- than alloy junction types. Furthermore they will ous precautions. · . operate at much lower levels of collector current We may now sum up the last two types. The and voltage. The· two tables below compar~ alloy junction transist·or makes an excellent typical MAT's wi·th the best alloy junction and A.F. transistor down to fairly low levels of · alloy diffused ty·pes on the market. • • J' 1 i 6 22 TESTED CIRCUITS l SlNG MICRO Al.l.OY TRANSISTORS . ! . , . ..1 Table J.-Co1npa1·is·on1 between MAT and best A.F. transistor hitherto available. I I ! V ce(sat.) Beta lc(max.) ! MAT 0.05V 75 . 25() 50mA Alloy junction 0.15V 20 90 50mA . From this it will be seen that
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