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Moderize Your Williamson Amplifier

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Moderize Your Williamson Amplifier 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 The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors ♦ PDF Cover Page ♦ ♦ Verso Filler Page ♦ MODERNIZE '10"" 'W� II� HE of extreme linearity. hs prefl:rrN oper· T Williamson amplifier circuit was performance is required. Even this mini· hrst publicized in Enlland in 1947, mum will probably be: inctcaScd in the ating conJition is as a pentO\lc: ;although .10.1 in Ihis counny in 1949. It has ycan to come unless the c:fficiency of the: manufacturer furnishes trio.. le r;acin�s .u:hievc. .. 1 wiJe acceptance and popularity, loudspeaker sYStems can he increascd. for che tube. rri,,..le UI'l'r;alion r�'sults in .111.1 lI.n 1",,,11 the basis for K'veral modi· Por theM: Itnd relatN reasons. c:lfuru higher .JislOrriulI an,1 rl",h• .:e.. 1 powl"r vut· hl'ations of the: ori,inal desian. The: have bcc:n devoted to increasinl, the: put. The convencional ultra· linear con­ . · mnS( billsic change was the: ulrra-lincar power OUtput of audio amplifien. The ncecion cannot provide opcimum rc:sults version of operation, which I developed advent of some new tube: t}·pes ha', made wich dICse tubes either, since there is no anJ subsequc:ntly Jc:scribcd• . This ar­ this praCtical within the W:lliamson type of operation more linear than che rangement corrected 2 of the: basic de­ configuration without the n�cd for com· pentode conneccion for which chey were he ic:ncic:s in the: original desiln - it pletcly tebuilding the amplifier. Changes designed. As will be: discussed later, increased the: powc:r caS-bility of the: required arc replacemc:ne of the output however. a compromise form of opera· amplifier to n or 30 wattS, and it irn­ tubes, substitution of an output trans· tion fits the necJs of che Williamson proVN the: marlin of feedback stability. former which will handle the: increased modernization very nicely. Now, as always happens. Pro,I'CSS in power and provide suitable impedance To dc:rive the: potential be:nefits avail· amplifier Jesi,n has continued: it is matchin& and addition of fixed bias. able in these: tubcs, proper impedance pussible to make furthe:r improvements macching muse be: obtainc."! in Ihe out· in 'the Williamson Jcsigrf'(both triode , New Output Tubes put transformer, The Ornaco A-430 and ultra·linear venions). These im­ The: new tube: selected for modernization transformer has bc:c:n dc:signed specifi· povements again correa for limitations of the: Williamson is che Amperex cally for chis purpose. This is a �O-watt with respect to power OUtput and ('CA7, which is also imponed anJ dis­ unit. che performance of which excI:cds stability. tributed as che: Mullard EL· H. This is Mr. WiIliamson's sIX-cificarions wich re· a compact tube: with power capabilities spect to frequency response. permissible Increasing Power Output up to 100 wans, depending on the sup· feedback. power handling ability. ;and so Present thinking 00 requirements for ply voltagcs available. Ir can be: plulled on. At presenc this is the only commc:r· .IuJio P�W" js vastly dilfercnt from that ditcCdy into che sockm formerly uscd cial transformer of corrt'Ct impl-Jance. nf a few yean ago. Then, most people for �RRI',. KT(,(,'s, 161<'1·s. ;an.! mher hut it is anticipate.1 thOlt orhl"rs may he: , .. id, · .... l"n waus is enoush for me." tubes of this type, with the single: aJJi· available soon. Now, however, modern program ma­ tional requitement that the No. I pins The Dynaco A·4.30 has primary taps terial has bcc:n increased in dynamic muse be: grounded. which can be: used to furnish aboue 10% range many times over that of former The: 6CA7 JEL. 34 is a pentode tube: screen loading. This does noe cause de· �l:ars. This fact alone: has increased the: power requirements substantially for realistic, undistoncd teproduCtion. In addition, source material frequency re­ sponse has been cxtended, and this also introduces the: need for a te-cvaluation lIf amplifier power requirements. In­ crcascJ frequency response means that the amplifier has to handle power at greater ntrcmes of frequcncy. At these: e xtremes, the impedance characteristics of the loudspeaker change from the: nominal values. This means that the amplific:r is mismlllcheJ at frequency ex· tremes, and a mismatch dccrc:ascs the maximum.powc:r cap.bilities of any ;amplific:r. To Jc:liver clean power into a loud­ 'Ilt·,.lel·r IlIa<I, an amplifier must be: cap­ . .. .• ble of at least ,,,,ic, the: power rcquir<.... �' . for a resistor load such as is usedn i ���. .----4--r---"."..........,....-.J ••$0"'. Ill<::uuring and ratin" amplificn. Thus the ex tension of both dynamic range and ,:;&:'000. _. frequency range in modern rccordinll. I'M sourCl"s. and tape means that 2� w.IttS are ;about a 1fIilfi1flllm if top-grade " NOT( _•• " ,IN LA." T"", ..... , "se ""\, .... ",cas. OT"'. .• iOONOT uou_o elN". 'A� ... 'Hatler. D and Kef_ H. I,. "Improyin& the " '.lv. "'•• " MA., ......, Ot"(IIt',,, I' FILA"'", c.1.CulT '. wA6.ulS OIH."Ou.c ON O"IGI� W,Uiem... Ampliller". HaoUe .. T�N..... " '.OuNOCD "( ....�I ...bn .,)' 1953. ... .......c:;,( .. , .. , ""(D. '''''se .. ,'� 00 ..or ......I TO.' C ......CEO. di AUIlIOCltAFT I\fACAZINE hi8hct ratil1�) arc \V1f�-J III serieS i fom this junction, with the negative rl"Ctilier I 'l'rminal� tow;lr,1 rhl." ""trut �i,'(·. Th .. rl·s:.rhinH negative OC is filtl."rl-J by a IO.OOO-ohm potcmiomercr and a 47,· OOO-ohm fixed resistor, and the arm of the pot is bypassed by • 40-p.fd (or greater ) , I �O·volt Cllpacitor. This is shown in the diagram. Fig. 1. The po­ tc:ntiomerer can be placl-J conveniently in the hole that formerly hcld the bias· balancing pot. A bias-balance adjust. ment is no lonlter required, since the OUtput transformer is of • design in which performance is noc deteriorat�-d by moderate current unbalance, Ind the rubes used do not have much vari;!tio:l in plate current drain. The new potentiometer controls the bias voltage, which is fed to the bottom ends of the two IOO,OOO·ohm outpUt. tube grid resistors. These, of course, are no longer connected to the components formerly used in bias balancing. The combination of chan,ltes descriheti above has inc:rC';lSc:d the !'uwer ut the i amplifier to about twice iu ultra· lincar ·i rating and about 4 times iu trioJe rating. This dunge alone makes In im· po"ant improvement, but an equally important improvement can also be , made by extending the stability margin i of the amplifier. J Stabilizing the Amplifier Criteria for good amplifier design have changed in recent years, and the stress is now being placed more and more on :rioration of the extreme line:uity of plifier) . It fits the space, despite its lar.fl:e am plifier stability. Many amplifiers, t s, and it does h ve the advantage size, because it hu no flanges. Insr.alla· the ube a while performing well under steady-state of lowering the nternal i ance tio the transformer requires no me­ i mped (for n of conditions, have exhibited muddy and damping). further, it improves chanical alterations in the chassis except, . bener harsh qualities when reproducing music. the inherent regul.uion of the output possibly, reaming the mo nt ng holes to u i One reason for this is the fact th;!t stage to he point where no changes need acco modate mounting sruds.
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