TL-102 = Amplifiers In Parallel – Instructions for constructing a circuit using an Altec 15067 Autotransfomer that makes it possible to parallel the outputs of two power amplifier. May 16, 1960.

TL-103 = Loss In Telephone Cable Circuits – Informative Chart. May 16, 1960.

TL-104 = Zone Volume Control – Instructions for building a zone volume control for distributed, 70-volt speaker systems. May 16, 1960.

TL-105 = Area Covered By A Horn Beam – Subtitled “A Problem In Geometrical Projection”, this Technical Letter is an excellent resource for those wishing to get in on the basics of the behavior of multicellular and sectoral horns.

TL-106 = Altec 70-Volt Matching Transformers – Excellent information on Altec transformers for use in 70-volt distributed sound systems. Includes pictures, charts, and comparisons with competitive products of the time.

TL-107 = Essential Requirements For Speech Reinforcement Systems – An excellent early paper on application and design of sound systems. Often misunderstood by today’s system designers, these principles are A MUST SEE!

TL-108 = Sound System Power Requirements – Our old friend Don Davis’ influence really begins to shine through with this Technical Letter. Another excellent paper on proper design of amplifier power requirements for sound systems that gives principles most designers today have forgotten (if they ever knew). Includes a helpful nomograph.

TL-109 = Ventilation Or Sure Death – An interesting TL regarding the importance of keeping transformers in sound systems cool, and so increase their life expectancy. Note the references to owners of Altec sound systems keeping them for 30+ years.

TL-113 = Loss Due To Speaker Lines – Excellent instructions for calculating the size of wire needed for a specific application.

TL-121 = Protection For High Frequency Driver Units – Dr. John K. Hilliard’s expertise in making applications of Altec Lansing products interesting, understandable, and practical show here. Includes information on AL passive crossovers and protecting HF drivers from static discharge.

TL-122 = Line Voltage Compensation – Another Hilliard-influenced Tech Letter for those who have problems with varying power sources for their sound system equipment.

TL-123 = Altec 755C Loudspeaker – An interesting TL replete with application information and frequency response charts for this very famous speaker.

TL-124 = Output Power and Maximum Gain – More technical information forgotten by the modern sound system designers/installers. Covers concepts and includes a chart about calculating electrical gain in Altec sound systems.

TL-128 = Altec Voice Warning System, Part 1 – Pages 1 – 8 of the original manual on how to design and install a properly operating Emergency Warning System using voice projection. Later called “BIG VOICE” and then “GIANT VOICE”, systems of this type are still the BEST way warn the public in an emergency.

TL-128 = Altec Voice Warning System, Part 2 – Pages 9 – 12 of the original manual on how to design and install a properly operating Emergency Warning System using voice projection. Later called “BIG VOICE” and then “GIANT VOICE”, systems of this type are still the BEST way warn the public in an emergency.

TL-128 = Altec Voice Warning System, Part 3 – Pages 13 – 16 of the original manual on how to design and install a properly operating Emergency Warning System using voice projection. Later called “BIG VOICE” and then “GIANT VOICE”, systems of this type are still the BEST way warn the public in an emergency.

TL-133 = Standard Pads – An invaluable tool for designing audio pads. Every sound system designer and installer should have and use this!

TL-134C = Typical Specifications for Altec Lansing Voice Warning Systems – Originally prepared for Vandenberg Air Force Base, these specifications were for system designers to use as a basis for writing “specs” for similar systems they might be called upon to design for bidding. Circa 1963.

TL-135 = Typical Mounting Of Three #31A Horns For 360-degrees Of Coverage – Interesting.

TL-136 = Engineering Information For The 695A Microphone

TL-137 = Altec 21BR Microphone – A complete listing of all of the versions of one of the most famous of all the Altec microphones.

TL-139 = Wind Noise Reduction In Microphones – Windscreen applications for the famous Altec M-20 and M-30 Condenser Microphone Systems, many of which are still in use. Nothing sounds better!

TL-140 = Special Application For the 695A Microphone – One of the BEST of all of the hand-held paging/announcing microphones ever built by any manufacturer, the Altec 695A Noise Canceling Transistor Microphone, this TL shows how to adapt it so that there will not be any  “switching pops” when in use.

TL-141 = Handbook Of Altec Sound System And Installation Data – Again, our friend Don Davis’ abilities to educate shine through in this, the first thorough manuals on “how to” design a properly functioning sound reinforcement system. Topics covered include: Time Delay; Accessory Panels; Priority Systems; Compressors; Impedance Matching; Hybrid Transformer; Signal Circuit Wiring; Cable Capacity; Design of Standard Pads (almost NO ONE knows how to do this today!); Voltages for Various Power Levels; Number of dB for Voltage or Current Ratio; Electrical Power vs Electrical Power Level; SPL vs Acoustical Pressure; Length of Cable vs Loss at 10 kc & 20 kc. FASCINATING and another MUST READ for all those in the design and installation of sound reinforcement systems!!!!

TL-143 = Adapting the Altec 695A Microphone For Use With Altec 1568A and 1569A Amplifiers

TL-145 = Modification Of Altec 351C Amplifier For Use With Altec 695A Microphone

TL-146 = Altec 351B Modification For Microphone Operation, Using Altec 1578A Preamplifier

TL-147 = “Profitable Business Management” – Address given at the 1964 Altec Lansing Seminar by Mr. C. R. Rininsland, Altec Lansing’s VP of Finance. Very good!

TL-148 = Two Papers On Microphones – Presented by our good friend, Mr. Bill Hayes, at the 1964 Altec Lansing Conference, this TL covers very interesting and valuable information about the design, construction, and use of high-quality microphones.

TL-149 = “Over 40 Years In The Sound Business” – This address, which was given at the 1964 Altec Lansing Conference, was presented by Mr. Milton Boom, President of BOOM Sound Engineering of Chicago. One of the most interesting men to ever be in the sound business, Mr. Boom presents his experiences in a manner that is both informative and entertaining. EVERY person interested in sound systems needs to read this gem!

TL-156 = Two Papers On Selling – Second only to Dr. John K. Hilliard, W. H. Johnson was THE PREMIER of all salesmen for Altec. These two papers, “What Is A Salesman” and “Satisfied Customers (the function of selling)”,  ought to be required reading for everyone in sales operations, regardless of their field of selling. DON’T MISS THIS ONE!

TL-157 = The “How” and “Why” Of Writing Altec Specs

TL-158 = Acoustical Tube Delay System – One of the finest men to ever work for Altec, Ed Seeley worked for ERPI, and came along with George Carrington, Alvis Ward, etc., when the formed the All Technical Service Company in 1936, and stayed with Altec until his retirement. Mr. Seeley wrote this interesting article on pre-digital delay problems and a practical solution to them! Mr. Seeley died not too long ago of Alzheimer’s disease – a sad thing to happen to such a great mind!

TL-159 = Objective Technical Specification for the Altec M50 Solid State Condenser Microphone System

TL-160 = Advertising Sales Brochures – VERY INTERESTING! A neat set of examples of Altec’s sales literature in the mid-1960’s.

TL-162 = Sound Coverage: Degrees vs Distance – Still accurate and up-to-date, this TL from Don Davis shows how to calculate coverage for a ceiling-mounted distributed loudspeaker system. EVERY SOUND SYSTEM DESIGNER & INSTALLER SHOULD READ THIS ONE!

TL-163 = Amplifier Comparison Tests – A VERY GOOD primer on how to test power amplifiers for output performance.

TL-165 = Altec “TRUTH BOX” Transformer Demonstration Board – Even today, those who saw the Altec “Truth Box” in operation vividly remember it’s ability to demonstrate how cheaply built most “other” transformers were. Someone ought to build one and test TODAY’S transformers – it might be quite surprising to hear the results…

TL-162 = Sound Coverage: Degrees vs Distance – Still accurate and up-to-date, this TL from Don Davis shows how to calculate coverage for a ceiling-mounted distributed loudspeaker system. EVERY SOUND SYSTEM DESIGNER & INSTALLER SHOULD READ THIS ONE!

TL-166 = Decibels – Don Davis is at it again: training Altec Engineering Sound Contractors and acoustical consultants how to understand the behavior of sound and help them design and install better systems!

TL-167 = Quick Reference Chart For 70-volt Systems – Another Tl that is still useful today! Shows watts, dBm, Load Impedance, & Speaker Wire Size.

TL-168 = Graph Relating Thermal Noise To Bandwidth – Jim Noble was one of the really brilliant minds at Altec during it’s heyday. In this TL, he gives a simple illustration as to the proper way to design a noise-free sound system.

TL-169 = Instructions For Detailing “Typical Specification” Sheets – In this TL, Jim Noble shows how Altec developed the format of the “spec sheet”. Still in use today, and largely unchanged, this is a VERY interesting piece of Altec history. March, 1967.

TL-170 = A Collection Of Questions By Sound Engineers Concerning The Alternating Current Meter

TL-171 = 70-volt Line Impedance Bridge – Our ever-practical friend Don Davis wrote this TL to help Altec sound contractors make sure that the systems they install perform without failure. Still accurate and up-to-date, EVERY SOUND SYSTEM INSTALLER SHOULD READ THIS ONE!

TL-172 = Peak Factor Demonstration Test Set – Altec’s Lou Graner shows how to build a test set that will show the difference between RMS voltage and the true peak voltage encountered in the complex waveforms of music and speech.

TL-173 = Portable Peak-Responding Voltmeter, Calibrated In RMS Volts – In this TL, Lou Garner shows how to build and use this device.

TL-174 = DC Capabilities Of Altec All-Solid State Amplifiers – Altec’s Jack Shechtman gives a veritable gold mine of valuable information regarding Altec’s early solid-state amplifiers.

TL-175A = Replacement Transistor List – Much like a “tube substitution chart” for vacuum tube radios and televisions, this TL gives invaluable information owners of older Altec solid-state amplifiers when in need of repair.

TL-181 = Inverse Square Law Calculator – As our friend Don Davis pushed the Altec contractors and acoustical consulting community into ever-deepening seas of sound system performance prediction and design, this TL became the cornerstone of all that he and his dear wife Carolyn would spend the rest of their professional careers doing: writing, training, and educating. EVERY SOUND SYSTEM DESIGNER AND INSTALLER SHOULD READ THIS ONE!

TL-182 = Engineering Loudspeaker Locations – Another milestone in the writings of Don Davis, the principles for proper loudspeaker system design – largely forgotten today – are well explained here. Another MUST READ for EVERY sound system designer & installer!!!!

TL-183 = Directivity Of Loudspeakers And Microphones – Written by our friend and colleague, Don Davis, this is one of the BEST articles ever written on the subject. Includes a reprint of the now famous paper on the subject by Hopkins and Stryker.

TL-187 = Altec 9473A Limiter Amplifier – Specifications for this early two-channel limiter. Interesting!

TL-192 = Amplifier Impedance Effects On The Transfer Characteristic Of Filters And Equalizers – Altec’s Director of Engineering, Jim Noble, shows how to make certain that the input impedance to Altec amplifiers is not altered by external filters or equalizers. Interesting!

TL-196 = Calculating And Using Critical Distance – Here’s Don Davis again with a TL that, coupled with TL #’s 181, 182, & 183, makes for excellent reading. It would do the modern generation of system designers and installers to read it!

TL-197 = Calculating The Maximum Electrical Power Required – Again Don Davis shows us methods now forgotten by modern system designers (until something blows up). How often have we seen systems shut down when the A/C power breakers tripped because the designer or installer forgot (if he ever knew) the principles laid out here?

TL-198 = New Ways To Look At Potential Acoustic Gain – As we get into the second generation of sound system designers and installers who have never heard of PAG/NAG, it would do them well to read this! Thanks Don!

TL-199 = Finding A Realistic EAD – Don’t know what EAD is? Well, it’s not surprising! Read here to find out as Don Davis – again – makes it clear how to design sound systems that work BEFORE they are installed!

TL-201-A = Useful Directivity Data For Reverberant Sound Fields – Altec’s Chief Engineer in Acoustics, Bob Beavers, gives valuable directivity information on famous Altec horns, including the 811B, 511B, 311’s, and multicellular models. If you use these horns, this will interest and hep you!

TL-202 = Modification of Altec 1591A Compressor For Use As A Line Amplifier In Altec Acousta-Voicing Network

TL-203 = Measurement of Nominal Sensitivity Ratings For Horn-Driver Combinations Commonly Used In Acousta-Voicing – An interesting TL on the performance of large-format Altec Lansing drivers and horns. A similar one for the smaller horns can be found as TL # 220.

TL-204 = Altec Rotary Attenuators

TL-205 = High Frequency Driver Protection Capacitor For Biamplified Sound Systems – Written by Paul Spranger, this is another excellent article for those who design or install professional sound systems.

TL-206 = 1588B Gain And Overload Characteristics

TL-207 = Useful Directivity Data For Reverberant Sound Fields – Altec’s Chief Engineer in Acoustics, Bob Beavers, gives valuable directivity information on famous Altec horns, including the 811B, 511B, 311’s, and multicellular models. If you use these horns, this will interest and hep you!

TL-207 = A More Accurate Way Of Calculating Critical Distance – Here’s Don Davis again – pushing the envelope in an MUST READ Technical Letter!

TL-208 = Architectural Uses Of The Critical Distance Concept – More from Don. Another essential paper for all sound system designers, users, and operators! Published February, 1972.

TL-210 = Calculating Percentages, Pages 1 & 2 – EXCELLENT materials on how to conduct your sound contracting business in a more business-like manner. Pages 1 & 2.

TL-210 = Calculating Percentages, Pages 3 & 4 – EXCELLENT materials on how to conduct your sound contracting business in a more business-like manner. Pages 3 & 4.

TL-210 = Calculating Percentages, Pages 5 & 6 – EXCELLENT materials on how to conduct your sound contracting business in a more business-like manner. Pages 5 & 6.

TL-210 = Calculating Percentages, Pages 7 & 8 – EXCELLENT materials on how to conduct your sound contracting business in a more business-like manner. Pages 7 & 8.

TL-211 = Notes On Loudspeaker Directivity – One of the most ignored and misunderstood concepts in the sound system design world today is that of loudspeaker directivity. In this TL, Don Davis again shows why he is so well able to communicate these important concepts in an understandable manner. DON’T MISS READING THIS ONE!

TL-212A = Useful Equations For The Sound Contractor – A basic primer on the equations that every sound system designer USED to know how to use when designing a system. If every acoustical consultant, system designer, and sound contractor would learn and use them again, the quality of the systems being designed and installed would improve tenfold!

TL-213 = Using The General Radio 1564 Analyzer To Measure THD

TL-214 = Time Delay Calculations – Any sound contractor who has tried to set a digitally delayed loudspeaker systems needs to read this!

TL-217 = Using Altec Line Transformers and Autotransformers With European 100-volt Speaker Distribution Systems

TL-218 = Acoustic Attenuation With Increasing Distance – Here’s a great TL by Don Davis that will help ANY sound system designer, installer, or user! It’s amazing how much has been forgotten…

TL-219 = Improving The 1605A NOALA For Operation Under Adverse Noise Conditions – Altec’s Bob Bird, a true genius in electronic design and application, developed the first properly operating automatic level control for paging systems called NOALA – “Noise-Operated-Automatic-Level-Adjustment”. The NOALA worked so well that many are still in operation all over the world. Only the advent of digitally-controlled sound processing e equipment made it possible to improve upon his design.

TL-220 = Measurement Of Nominal Sensitivity Ratings For Horn-Driver Combinations Commonly Used In Monitor And Playback Systems – Similar to TL #203, which deals with the larger AL horns, this is an interesting data on the smaller Altec horns.

TL-221 = Directivity of Altec Loudspeakers – Mark Engebretsen’s excellent paper on loudspeaker Q verses frequency.

TL-222 = Application Of Telecommunication Products To Commercial Sound Use

TL-223 = Altec Horn-Driver Sensitivity Ratings In Metric Units – Some very helpful information for those who still use the Metric system of measurement.

TL-224 = Examples Of Simplexing For The Sound Contractor

TL-225 = Modifying The 9860A Active Equalizer For Low-Level Signal Applications

TL-226 = Measuring Loudspeaker Impedance By The Constant-Current Method

TL-227A = Notes On Noise Masking/Speech Privacy Systems – Interesting TL by Richard Forbes and John Eargle (before he went over the the dark – orange – side)…

TL-228 = Understanding And Using Hybrid Circuits

TL-229 = Control Of Feedback In Systems With The White Model 3900 Narrow-Band Filter Set – A GREAT primer on system equalization!

TL-230 = Application Of Component Loudspeaker Power Capacity Ratings To The Design Of Two-Way Systems – Mark Engebretsen’s EXCELLENT Technical Letter on how to determine the manner in which a loudspeaker will perform without failing, rather than merely rely on a manufacturer’s spec sheet.

TL-231 = Three New Compression Drivers – Mark Engebretsen and Bill Hayes introduce Altec’s 288-8G (there’s a nice chart comparing it’s performance to the JBL 2440), the 291-16B, and the 290-4G.

TL-232A = Equalization Techniques And Practices – Our long-time friend Ted Uzzle wrote this sterling paper on the proper use of equalizers in live sound reinforcement systems. A MUST READ!

TL-236 = Control Of Radio Frequency Interference In Sound Systems – Paul Spranger wrote these instructions for controlling RFI in sound systems – another MUST READ for system installers!

TL-237 = Directivity Response Of Single Direct-Radiator Loudspeakers In Enclosures – Clifford Henrickson authored this exceptional paper on a incredibly misunderstood topic.

TL-241 = Applications For The Altec Lansing MANTARAY® Constant Directivity Horns – Our friend Chris Foreman wrote this helpful and practical paper on how to use the BEST constant directivity horns ever designed or built to date – the Altec MANTARAY’s!

TL-242 = Applications For The Altec Lansing 1690 Mixing Console – Here’s Chris Foreman with a TL on how to use one of the nicer  mixers that Altec made – the 1690.

TL-255 = Coverage Of Altec Lansing Loudspeakers – Ted Uzzle’s expertise in making the complex understandable and usable is easily seen in this, the FIRST application of modern computer-assisted loudspeaker coverage and system design techniques. Still a valuable tool for understanding how loudspeakers work, it is a valuable addition to the knowledge of sound system designers everywhere. June, 1981.

TL-257A = Sound Distribution On A Plane Normal To A Loudspeaker Axis – Rex Sinclair authored this paper on designing distributed loudspeaker systems. Very nicely done!

TL-258B = Uniformity Of Coverage In Distributed Sound Systems – Rex Sinclair again enlightens us on this important and often misunderstood topic.

TL-262 = Coverage Of Multiple MANTARAY® Horns – Our friends Mark Ureda and Ted Uzzle teamed up to write a paper whose concepts are still not understood by most modern acoustical consultants, sound system designers, and sound contractors – how to cover large areas with multiple horns while minimizing phase interference, and maintaining apparent apex. Another MUST READ!

TL-263 = Modifying The Altec 2204 Power Amplifier For 16-ohm or 70.7-volt Operation – Again, Ted Uzzle’s years of cinema work shine through as he describes how to get the most out of a wonderful amplifier, the Altec 2204.

TL-264A = Using Thiele-Small Parameters – Rex Sinclair wrote this outstanding paper on how to use Thiele-Small parameters to design loudspeaker systems. Every loudspeaker designer should read this one!

TL-266 = Articulation Loss In Consonants For Distributed Sound Systems – Rex Sinclair’s expertise with distributed sound systems shows up again in this often ignored design topic.