Radio Broadcast (May 1929-Apr 1930)

.RADIO BROADCAST ADVERTISER. Sweetest of Loud Speakers*— It's a Real S-M! ONLY two months old is the S-M dynamic speaker: yet already it has taken its proud place among S-M audio products — the acknowledged aristocrats of tone quality. . . "Stveetness" is taking on a new meaning for owners of S-M speakers. All the mellow flow of the "lows," as well as the brilliancy of of the "highs," come out smoothly on an S-M dynamic — with a surprising absence of all rumbles, roars and rattles. . . As always, there are underlying engineering reasons. Sound design in the speaker head is coordinated with similar mathematical correctness in the built-in S-M 229 output transformer, which has various taps to insure proper impedance matching for 171A, 210, 245, or 250 type tubes, singly or in push-pull. . . The 110-volt d.c. type (851), at $29.10 net, is ideal where the field winding is to be connected as a choke in a power circuit. . . The a.c. type (850), at $35.10 net, operates on 50 to 60 cycles, 105 to 120 volts. Thorough rectification of field current, with a 280 tube and a 2-mfd. filter condenser, reduces hum to the point of defying detection. . . Either type fits an 8V2" baffle hole. . . Try an 850 or an 851 unit in the next set you build — and the S-M speaker will become your speaker! S-M 850 Dynamic Speaker 105-120 volts, 50-60 cycles. 720AC Screen-Grid Six (All-Electric) The 720AC is giving to experimenters everywhere a preview of radio as it will be in 1930 — combining the sensation of the 1928 season — all-a.c, operation — with the sensation of 1929 — screeri'grid r./. amplification — and with them the entirely new 1930 features of a screen-grid tube almost 100% better than the d.c. operated '22, and a moderate-voltage output tube (the *45) nearly as powerful as the high-voltage *50. And, with these, the S-M precision engineering which has brought in broadcasting from across the Pacific with six tubes — and even with four. S-M tone quality is the accepted criterion of the audio transformer industry. All these things in the 720AC (licensed under patents of RCA and associated companies), at only $70.20 net for the set completely wired in the 700 two-tone shielding cabinet, less tubes and power units. Component parts total $47.07 net; cabinet $5.55 net additional. S-M 669 power unit, furnishing all A, B, and C power required, wired complete $34.50 net. S-M 720 receivers can be changed over at slight cost to the 720 AC circuit; full directions in Data Sheet No. 10. " Round the -World Four" (Short -Wave Sets) Bigger and bigger grow the thrills that are coming in on the short-waves — biggest of all when received clearly on an S-M Round-the-World Four. One screengrid r.f. tube is used, with regenerative (non-radiating) detector and two S-M Clough-system audio stages. Wired complete in the aluminum cabinet shown, (Type 730) with coils giving 17 to 200 meter range, $42.90 net — or as a two-tube adapter (Type 731) for use with any broadcast receiver, $30.00 net. Component parts also available, at $31.71 net for the 4 tube set, or $22.86 net for the 2 tube adapter. New 810 Drum Dial As beautiful an illuminated dial as you will find anywhere, in the highest-priced receivers. Smooth — absolutely quiet — rigid and accurate — a full '/f6' for each of the 100 dial divisions — and only l'/ie' thick over all — truly a dial to delight the heart of the setbuilder with modern ideas. Obtainable for condensers to right or to left of dial; 810R or 810L, price $2.25 net. Are you getting the Radiobuilder, a monthly publication telling the very latest developments of the SM laboratories! No. 11 (Mar. 1929) gave the first details of the new 720AC All Electric Screen Grid Six, and the 669 Power Unit for the new a.c. screen grid and 245 tubes, with complete circuits. Send the coupon for free sample copy, or to enter your subscription if you want it regularly. If you build professionally, but do not have as yet the S-M Authorized Service Station appointment, ask about it. SILVER-MARSHALL, Inc. 6403 West 65th St., Chicago, U. S. A. Silver-Marshall, Inc. 6403 W. 65th St., Chicago, U. S. A. .... Please send me, free, the 1929 Summer S-M Catalog; also sample copy of The Radiobuilder. For enclosed in stamps, send me the following : . 50c Next 12 issues of The Radiobuilder . $1.00 Next 25 issues of The Radiobuilder S-M DATA SHEETS as follows, a 1 2c each: .No. 1 .670B. 670ABC Reservoir Power Units . No. 2. 685 Public Address Unipac .No. 3. 730. 731, 732 "Round-the-World" Short Wave Sets .No. 4.223, 225, 226, 256, 251 Audio Transf ormers . No 5 . 720 Screen Grid Six Receiver .No .6. 7 40" Coast-to-Coast" Screen Grid Four .No. 7.6 75ABC HighVoltage Power Supply and 676 Dynamic Speaker Amplifier .No. 8. Sargent-Ravment Seven .No. 9. 678PD Phonograph Amplifier ..No. 10. 720AC All-Electric Screen-Grid Six. . .No. 12. 669 Power Unit (for 720AC) Name • may, 1929 page 3 0