MAY, 1960 50¢ / .. A NEW LOW-NOISE TWIN TRIODE to improve performance and simplify the design of Audio Pre-Amplifier Stages Low noise, high performance, moderate cost­ provided by the new RCA-6EU7, a high-mu, nine­ pin miniature twin triode designed especially for high-gain, resistance-coupled, audio pre-amplifier stages-in high fidelity amplifiers (monaural or stereo), amplifier kits, tape r 2corders, juke boxes, and public address systems. Noise and hum are minimized by the use of double­ wound, helical heaters, and a new base layout which keeps heater leads well away from the grid leads. Low microphonism, high mechanical strength, and reli­ ability are assured by a short, rugged cage which provides sturdy support for the tube electrodes. New base arrangement also simplifies stereo to Stereo layouts. The accom­ C hannel 2 panying diagram shows how the basing arrangement facili­ tates the design of an amplifier using the two to Stereo triode units for isolated Channel l stereo channels. For technical information, contact the RCA Sales Repre­ sentative at our office nearest you, or write directly to RCA Electron Tube Division, Commercial Engineering, Section E-9l-DE, Harrison, New Jersey. EAST: 744 Broad Street, Newark 2, N. J. HUmboldt 5-3900. MID-WEST : Suite 1154, Mercha.ndise Mart Plaza, Ch icago 54, 111. WHitehall 4-2900. WEST: 6355 E. Washington Blvd., Los Angeles 22, Cal. RAymond 3-8361. • The Most Trusted Name in Electronics ~&: RADIO CORPORATION OF AMERICA ~® 6 t Progress Re1JOrt #1 jTom GarTard LaboratoTies THIS E~PERIMENTAL TONE ARM WILL TRACK 40,000 MILES BEFORE WE UNVEIL IT FOR YOU The tone.arm on the Garrard you buy today was .once an experimental modelli.fs,e this one. Tracking thousands of miles. Running the gamut of ever more' exacting laboratory tests under the critical eye.s of engineers who have literally grown up in the Garrard tradition. That's why today's Ga1"rard equipment is the world's most advanced. Why, too, the exciting new ideas now on the testing tables will introduce dramatic new concepts in tomorrow's record playing. Now, as for 40 years, you can look to Garrard laboratories for the meaningful advances in the world's finest record playing equipm~nt. introducing the world's fore the 1000-cps tone was filtered_ (Per­ haps I should state here that harmonics are frequencies other than the one f ed into the amplifier. They are always multiples of the original, 01' fundamental, frequency. The first harmonic, 01' fundamental, is con­ l eollil BOUNTIFUL sidered to be the frequency in which we are interested-lOOO cps in this case. The second harmonic is 2000 cps, the third har­ monic is 3000 cps, and so on. In describ­ ing the test I could have said that all the first harmonic content of the signal ap­ pearing at the output of the amplifier is removed. All other harmonics are distortion since the note f ed into the amplifier did not contain harmonics or at least we hope that it didn't. In practice we can never get a source of tone which is completely free from harmonics, although oscillator distor­ tions of less than 0.1 pel' cent are r eadily the J ® obtainable. I do not wish to give the im­ pression here that all harmonics a re bad and unwanted. Musical instruments pro­ ore/co duce harmonics in addition to their funda­ (AG3400) mental tones to a greater or lesser degree, and it is in part, at least, by harmonic content that we can distingnish one musi­ cal instrument from another.) Probably the measurement about which MAINETa-DYNAMIC we have heard the most is that of fj'e­ DESIGNED to provide ultimate fidelity, stereophonic and mono- quency l'esponse determination. We feed in phonic . .. DESIGNED for highest vertical compliance . .. DESIGNED for a series of tones, all of which are at the same intensity. The output of the ampli­ instant compatibility with almost any system, any tone-arm . fier should reprodnce these with the same DESIGNED to completely safeguard the full fidelity of your records. relative intensity if we are to say that the Because of its extremely high vertical compliance, frequency r esponse of the amplifier is per­ the Nore1co Magneto-Dynamic cannot impair the fectly flat. To determine if this is true we quality of your valuable stereo records. Because of connect our same old resistor to the ampli­ its high output aqd the correspondingly lower gain fier; we also connect a good a. .f. voltmetel' demanded from your pre-amplifier, the Norelco whose characteristics are good to the lowest Magneto-Dynamic can be expected to eliminate the and to the highest tones in which we are problem of hum and noise in your system. Because interested. In other words, the meter itself the replacement stylus is completely self-contained must have a good - frequency response. with ~ts own damping blocks and self-aligning, you Meters for this purpose often carry a can, Ii you wish, change the stylus at home in a decibel (db) scale so that we can read the matter of seconds. response directly in terms of db without And these are only a few oi the abundant features having to convert voltage ratios into db. and advantages which combine to make the Norelco If the output of the amplifier is truly a Magneto-Dynamic the world's most bountiful stereo refl ection of the signal being f ed into the cartridge . .. ONLY $29.95 (including 0.7 mil dia­ input, the meter will not change reading mond stylus). For additional literature, write to: regardless of the tone being fed in. In North American Philips Co., Inc., High Fidelity other words, the intensity of the tone can vary and cause a change ill meter indica­ tion, but the frequency of the tone can P'OdU't~t 'ion, 23~ ' :okWillO, N. y ~~~NETO. change over a very wide range and should e produce no great change in meter indica­ tion. Another type of distortion measu I'ement in which we are interested is the squa1'e­ wave response of an amplifier. A square I; ,;~, ~~~C~~~E wave, because of its shape, is rich in har­ monics. If we fed a 1000-cps square wa.ve into our amplifier, we could see many har­ B monics. This measurement consists in de­ .~~ , termining how many of the harmonics con­ A taine£l in the square wave the amplifier is capable of reproducing. These are har­ monics which are introduced into the inzmt of the amplifier and are not produced by the amplifier itself. Note this fact in order to differentiate between this type of dis­ tortion and harmonic distortion. (Here r"o thin ~ods (A) c~mposed of a new platinum·cobalt alloy having ex· harmonics are intentionally introduced, and tremely hIgh coerclvlty, acting as armatures and diametrically mal' we are concerned with the amplifier's abil­ netlzed alon& their lengths are supported b, special butyl rubber ity to reproduce them in the same strength 'liearlngs and placed between two mu·metal pole pieces (8). The stylus (e) Is attached to a lever (D). Also attached to lever (D) are as they are contained in the original . vlscolold dampinl blocks (E) which are encased In a small metal sqnare wave. The amount by which the am­ clip that is Inserted into the housing of the cartridge. lever (II) Is plifier does not reproduce these square connected to the magnetic rods. by a W-sbaped couplinll body (F). waves ill a measure of this type of distor· Each half of th is coupling body can conduct stylus vibrations in one on only. In essence, this divides the overall stylus movement tion. No' standards have been set regarding its . two component vectors which correspond to th.- left and transient performance of amplifiers and channel modulations, and transforms these component vlbra­ other audio equipment) 10,000- and 20,000- Into ~ rotary movement of the corresponding magnetiC rod. rl0tatoons induce a varyinl flux In tfie mu metal pole pieces cps sqnare waves are commonly used. The h, n turn, induce signal voltages in the coil systems (G). output of the amplifier is loaded with the be specific advantages forthcoml~, from this s,stem Include' same resistor and with an oscilloscope. This emely high vertical compliance (more tban 3.5 x 111-5 em/drne): mely hllh output (mare than 30 my per channel at 10 cm/see) last instrument gives us a picture of the emely bleh chaanel separation (more than 22 db at 1.000 ke CPS); waves which are being reproduced by the I.. dynamic mass (2 mil. law st,lus pressure (3-5 ,rams) and vir. Iy no distortion. Frequen., respOll .. II flat trom 50 cps to ,. kc. • (Contin1te d on page 65) 4 AUDIO • MAY, 1960 SOulntR~fl SOulntR~ffll OUlntR~ DC the tape ' that cost , . , to perfect! Soundcraft Tape with the new FA-4 \:~:::::y formula­ tion. Designed to meet the unlimited challenge of the most exciting new era in recording history! Only years of research ... and the most modern and advanced before ... the full frequency spectrum for perhaps the very tape manufacturing facilities in the world ... could have per- first time! fee ted this tape! Soun<lcraft's new FA·4 FORMULATION is . frequency adjusted to provide the superlative sound repro- InsIst on Soundcraft Tape wIth the new FA·4 FORMULATION duction demanded in this exciting era of new discoveries and before you run another reel through your recorder ... you'll innovations in tape recordirtg. You'll hear "highs" as never never settle for inferior sound reproduction again! Gr:at Pasture Rd., Danbury, Conn.