PEARL's Miscellaneous Downloads Page

This page is posted as something of a precursor to the construction of our site.
Here we've made available a number of PDF files that will eventually be available from
our site's main navigation pages. In the meantime, and so that those viewing posts archived
on various servers will find live links in the future, we'll keep this page as permanent resource.

Complete Article Download Links   Previews
001 - PEARL CryoValve Tubes:
One fairly comprehensive page of process description followed by several pages of customer comments -- alright, raves -- on the sound of these tubes. The latest version includes a HiFi News and Record Review
interview with Ed Meitner of EMM Labs wherein mention is made of the benefits that accrue to cryo-treated vacuum tubes.


005 - PEARL RB300 3CX Data Sheet:
The RB300 3CX is a 300W anode dissipation rated, metal-ceramic, audio triode intended for low-velocity (i.e. quiet) fan cooling. Although not presently available due to difficulties with single-source supply the data sheet is nonetheless an interesting download.


010 - QUAD ESL-57 Rebuild & Modification:
245 pages of information on the QUAD ESL-57 that includes:
1) A 2009, Ken Kessler article on the ESL-57,
2) PEARL's complete rebuild of the original QUAD service information,
3) a compendium of Sheldon Stokes excellent work on repair and modification downloaded from
4) several pages from Stewart Penketh on panel module repair along with info on setting up the '57s in pairs and quads,
5) Peter Walker and D. T. N. Williamson's 1955, 3 part, Wireless World series of articles on ESL design,
6) the original UK and subsequent US versions of Walker and Williamson's patent on ESL technology in general and the ESL-57 in particular. All the patents have been rebuilt from the scrappy looking patent office originals into rather more presentable, readable, form . . .


015 - Altec Lansing 260A Product Literature:
This is a rebuilt version of the original literature for the Altec/Peerless, push-pull, 813-based 260W, 183lb power amp that while commonly mistaken for a boat anchor is in fact, an astonishing performer once modified.


020 - Altec Lansing "Voice of the Theater" Product Literature:
High quality , full color scans of a '60s vintage, 5 page, original Altec brochure. A nice little nostalgia trip . . .


025 - JFET Input, UL Cascode, Passive RIAA Stage:
While I don't suggest this is a "world beater," it has handily trashed any number of commercial offerings. It's presented here as a "freebie" and that's as far as the offering goes. If tech support is desired, you'll have "pay the piper" ( i.e. me) for the time it'll take to sort through your inquiries.


030 - W. Marshall Leach Jr. on the subject of noise:
Downloaded from
here and then collated into one large, navigable PDF.


1816 - Twinning Push-pull Audio Output Transformers:
This is a very brief, schematic description of a method for connecting pairs of single coil push-pull output transformers that materially improves the AC and DC balance of the composite pair so formed. AC balance is very important to low-value, high frequency distortion and feedback loop stability and is typically very poor in conventionally wound push-pull output transformers. The measurements shown for a Dynaco ST 70 output transformer illuminate the problem very well . . .


374 - Use of an Ideal Matching Transformer for Impedance Matching:
Excerpted from "Applied Electronics" published by the MIT Press


045 - Fostex NF-1, Near-field Monitor:
This is a very interesting speaker. Fostex have done some excellent research and FEA work to arrive at a cone shape not previously seen, one that opens a whole new line of inquiry for this developer.


050 - Cone and Diaphragm Materials:
Published by Pioneer Corp. about 1982, this paper is an excellent and thoroughgoing technical review of then-recent developments of materials for loudspeaker diaphragms in Japan. Detailed are developments of beryllium and boronized titanium diaphragms for high frequency applications and carbon-fiber reinforced olefin and polymer-graphite materials for use, in the former case in mid- to low frequency applications and in the latter, applications across the audio band.
Much information useful in the assessment of materials for diaphragm applicability is given.


1385 - Critical Damping: Missing Link in Speaker Operation Parts 1 & 2:
In audio reproduction, a subject of considerable importance to the high-fidelity enthusiast is amplifier damping factor and its effects on speaker operation. Misconceptions have arisen concerning this subject, and vague and incomplete answers have too often been given to the many questions involved.
Are the high damping factors found in present high-fidelity amplifiers byproducts of high-feedback circuits and, as such, unimportant in the operation of the system? Or is the ultimate, as some loudly proclaim, to have the highest possible damping factor built into the amplifier? Why does a particular speaker sound better with amplifier A than with amplifier B, although both show identical frequency response and power capabilities under bench checks? Why does that $2.00 speaker with the 6-ounce magnet (inefficiency and distortion included) seem in some cases to have more bass than the high-fidelity unit with the 5-pound magnet? Why is it that one enthusiast found reproduction more pleasing when he used a little current feedback from the output circuit yet another didn't when using the same circuitry? [ . . . ]




1386 - Loudspeaker Damping, Parts 1 & 2 - Albert Preisman:
Part 1. A discussion of theoretical considerations of loudspeaker characteristics, together with a practical method of determining the constants of the unit as a preliminary step in obtaining satisfactory performance.
"One of the considerations in the design and application of loudspeakers is the adequate damping of their motion. Thus, owing to the masses and compliances involved, the sudden application or removal of current in the voice coil tends to produce a transient oscillation of a damped sinusoidal nature. In particular, the sudden cessation of current in the voice coil may find the loudspeaker continuing to vibrate in the manner described, so that the sound "hangs over". Anyone who has experienced this unpleasant effect will seek ways and means to eliminate it."

Part 2. A discussion of theoretical considerations of loudspeaker characteristics, together with a practical method of determining the constants of the unit as a preliminary step in. obtaining satisfactory performance.
"We come now to the question of damping of the loudspeaker mechanism by the electrical circuit. In Fig 3 is shown the electrical equivalent of a loudspeaker illustrated in Fig. 2, with the addition of an electrical source of internal resistance RG feeding it. This normally represents the Rp of the output tube or tubes as viewed from the secondary terminals of the output transformer.


1387 - Acoustic Damping for Loudspeakers - Benjamin Bauer; Shure Brothers, Inc. Chicago, Ill:
The fundamental resonance of loudspeakers is recognized by many as a source of annoyance. Usually this resonance can be damped electrically by suitable selection of the amplifier impedance.
What is less well known is that damping can also be achieved by acoustical means incorporated into the loudspeaker or the enclosure.
This paper deals with the theory and methods for providing acoustic damping. It is concluded that transient response of loudspeakers and enclosures can be effectively controlled by acoustic damping. Furthermore, the response-frequency characteristic of the loudspeaker system need not be adversely affected, and it actually may be improved. Loudspeakers with acoustic damping may operate from high-impedance amplifiers without "hang-over." Performance characteristics become largely independent of the amplifier impedance.
Acoustic damping may be designed in a straightforward manner by ascertaining the acoustical constants and using standard experimental techniques of equivalent circuit analysis. We conclude, therefore, that acoustic damping for loudspeakers merits far more serious consideration than it has had heretofore.


1389 - Loudspeaker Enclosure Design - Damping with Acoustic Resistance - Parts 1 & 2:
This is a seminal piece of work that as far as I know has been completely ignored. Written in 1956 by E. J. Jordan , then in the employ of Goodmans Industries Ltd. UK, this paper outlines the manifold advantages of bass loading using what he called an "Acoustic Resistance Unit," an ARU, to control low frequency damping.
Completely unaware of Jordan's work, I independently developed his method about 1980 and have used it with great success ever since. I called it "Distributed Acoustic Impedances" or DAMPS and in the estimation of many, many listeners across some 3 decades it is simply the best bass loading method yet developed, far surpassing the ubiquitous Thiele-Small alignments for "reflexive," or, resonant, enclosures . . .


061 - Misleading Measurements - Raymond Cooke; KEF Electronics, UK:
It is not widely appreciated that acoustical measurements are prone to inaccuracies and that interpretation calls for a degree of experience and insight which is probably unequalled outside of medical diagnosis.
Testing out of Doors:
There are in fact very few really large anechoic chambers of first class quality in existence and of these, still fewer are available for loudspeaker measurements. For this reason measurements out of doors are often resorted to in an attempt to obtain precise results.


065 - Power Distortion:
Written by Kurt Steffenson of JoeList and
TriodeFest fame and edited by yours truly this is a post to the JoeList made about 2000. Kurt engages the matter of "current driving" bass units in a most intriguing article.




070 - The TungSol 5881 A New Beam Power Tube:
[ . . . ] For a long time there has been a growing demand for a tube with dynamic characteristics like the 6L6 but of a design that would cope more vigorously with the problems encountered in a heavy-duty audio output tube. After considerable experimentation, the TungSol design and development engineers have evolved a design which embodies many features which should qualify it as a successful candidate. This is experimental type (the RETMA commercial number is 5881), it has some intriguing features.




075 - The High-End Mythology of the Toroidal Power Transformer:
If you look at the AC power transformers used in most high-end audio equipment these days, you will find that a very large majority are toroid transformers. These donut-shaped transformers seem to have taken the high-end industry by storm. Their major advantage is that they do not radiate much of a magnetic field--a very useful property. Dealing with stray magnetic fields from EI-frame transformers (non-toroid) inside a high-end component is not a trivial undertaking. While toroidal transformers have one significant advantage regarding radiated magnetic fields, toroids have a number of "problems" that severely limit their performance in high-quality audio equipment. We'll try to help you understand what these problems are and show you how another kind of transformer, the EI-frame transformer can be a superior performer if designed, manufactured and installed properly. [ . . . ]




1150 - Inherent Feedback in Triodes:
The triode is imagined to be replaced by an infinite- impedance pentode with a fictitious EMF in the grid circuit to represent the back action of the anode on the field at the cathode It is shown how this transformation makes it possible to obtain practical triode circuit formulæ from conventional feedback theory. [ . . . ]




085 - Tonearm Geometry and Setup:
Optimum geometry of tonearms has been the subject of several articles over the last three decades, the earliest complete mathematical study being that of H. G. Baerwald in 1941. His analytical study of tracking-error distortion showed that optimum geometry of a tonearm of given effective length will have a corresponding offset angle and overhang. [ . . . ]




090 - Sylvania Gold Brand Electronic Tubes:
11 pages of original technical literature from Sylvania on their extensive line of truly premium grade tubes. Highly informative . . .




095 - Strategies to Repair or Replace Old Electrolytic Capacitors
Unfortunately, the selection of high voltage electrolytic capacitors today is both smaller and different from the past, so the chances these days are you won't find an exact replacement for your original equipment electrolytic.
For low voltage applications, like cathode bypass capacitors, most vintage types have an axial configuration, which is less common today but still available. The more modern radial configuration can also be used if their leads are long enough and they don't violate your notions of aesthetics . . .




100 - General Description of and Application Guidelines for Aluminum Electrolytic Capacitors - Nichicon Corp., Japan
An aluminum electrolytic capacitor consists of cathode aluminum foil, capacitor paper (electrolytic paper), electrolyte, and an aluminum oxide layer, which acts as the dielectric, formed on the anode foil surface. A very thin oxide layer formed by electrolytic oxidation (formation) offers superior dielectric constant and has rectifying properties. When in contact with electrolyte, the oxide layer possesses an excellent forward direction insulation property. Together with magnified effective surface area attained by etching the foil, a high capacitance yet small sized capacitor becomes available.




105 - Measurement of Noise Voltage in Chemical Batteries - Chadwick K. Boggs, Alan D. Doak, F. L. Walls - NIST
Ultra low noise voltage sources are often required in measurement systems and other applications. Common voltage regulators have performed inadequately in some applications. As an alternative, battery cells have been used. Of the various types, Hg cells have been credited with the best performance. However, actual values for the voltage noise in batteries have not, to our knowledge, been reported. In this paper a measurement system capable of measuring voltage noise below ·20dB nV/rtHz [about 20 dB below the equivalent input noise of the quietest JFETs and BJTs or all time ! ] is discussed and its ability to characterize experimentally high performance voltage references is explored. The results of such measurements on common batteries are presented, and potential applications are considered.

References included:

Thermal Agitation of Electric Charge in Conductors - H. Nyquist; Physical Review, July, 1928
"Dr. D. B. Johnson has reported the discovery and measurement of an electromotive force in conductors which is related in a simple manner to the temperature of the conductor and which is attributed by him to the thermal agitation of the carriers of electricity in the conductors. The work to be reported in the present paper was undertaken after Johnson's results were available to the writer and consists of a theoretical deduction of the electromotive force in question from thermodynamics and statistical mechanics."

Thermal Agitation of Electricity in Conductors - Dr. J. B. Johnson; Physical Review, July, 1928
"In two short notes a phenomenon has been described which is the result of spontaneous motion of the electricity in a conducting body. The electric charges in a conductor are found to be in a state of thermal agitation, in thermodynamic equilibrium with the heat motion of the atoms of the conductor. The manifestation of the phenomenon is a fluctuation of potential difference between the terminals of the conductor which can be measured by suitable instruments."

Design Considerations in State-of-the-Art Signal Processing and Phase Noise Measurement Systems - F. L. Walls, S. R. Stein, James E. Grey and David J. Glaze - Frequency and Time Standards Section, National Bureau of Standards, boulder, Co, USA
"Introduction - The recent rapid improvement of oscillator phase noise has resulted in significantly more stringent requirements for signal handling equipment. However, information concerning the phase noise performance of the two most important types of circuits - amplifiers and mixers - is often difficult to find. Some general principles are presented which allow one to estimate the phase noise performance of an amplifier. Also, techniques are described which permit one to obtain the best possible results from the traditional double balanced mixer. A measurement set-up which has 15 to 25dB improvement in its noise floor is shown in detail to illustrate proper mixer drive and termination. Although traditional circuits can with extreme care achieve [phase noise of] -175 dB or slightly better, this is not sufficient for all present requirements. One technique to obtain an additional improvement of 10 to 40 dB in measurement system noise is to reduce the mixer and amplifier contributions to the noise floor by the use of correlation techniques. A circuit to accomplish this is discussed along with some preliminary results."




Animated FEA of a Woofer Basket - Done by Ulrik Skol when he was running, this well illustrates the sorts of deflections commonly seen in such structures; exaggerated for clarity.