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Richard's Stuff

Technical Biography: Richard F. Sears, Kenly, NC 27542

Born November 6th, 1957, Farnborough, Hants, England



I have shown strong practical and technical aptitude from an early age.  I am an apprenticeship-trained toolmaker and studied mechanical engineering at night-school.

As a teenager I was keenly interested in vacuum-tube electronics, this interest being re-kindled over recent years with the design and construction of several vacuum-tube audio projects.

My professional life has been primarily that of a mechanical design engineer in the fields of high-pressure pneumatics and fire / explosion suppression systems.  In addition I have conducted original research in the field of fire extinguishing agents, culminating in a leading role in a DARPA sponsored ‘technology reinvestment’ program.  This program, under the “other” technology category, was won in the face of fierce competition from more than 100 other potential technology development proposals.  A major aspect of this program was the design and construction of an automated military aircraft dry bay explosion simulator.  I hold three patents in the field of fire & explosion suppression.

Support activities for the above engineering work included engineer and technician supervision, program cost analysis, hardware cost analysis, generation of technical proposals and program management.

I am a naturalized American citizen.   

Biographic Details.

As a kid, I showed a strong sense of practical and technical competence from an early age.  I built my first vacuum tube audio amplifier at the age of 11.  My father led me to comprehend the basics by guiding me in the construction of a common cathode triode (6F5) amplifier stage and the plotting of the transfer characteristics.  He then helped me to design a SE amplifier using a 6SL7 for gain and a 6V6 for the output stage.  I carried out all the construction myself including modifying an existing power transformer to provide the required HT voltage.  I calculated the required number of turns using data from F J Camm's “Coils, Chokes and Transformers” and then set about stripping the existing HT winding and replacing it, by hand.  The amplifier worked from the outset with no significant difficulty.  I then constructed a record player by building a plywood case and installing a speaker, the amplifier and a turntable.  I made my own pickup arm using Meccano.  The design of the record player included an “infinite baffle” box  for the speaker, using carpet underfelt to line the walls.  I felt that this constituted an improvement on the commercial inexpensive record players of the time which typically had a small elliptical speaker mounted in the side with the back radiating into the space under the turntable. 

Subsequent to this I played around with a number of Superhet AM receivers and later built several push-pull integrated audio amplifiers using 6V6s and 6L6s together with long-tailed and cathodyne phase splitters.  All of these worked, the latter ones fairly well, and sounded OK (at least to my ears at the time).

The other major project of note was the construction of an oscilloscope based on an adaptation of the Heathkit design.  I could not afford to buy much in the way of specified components and had to resort to ingenuity to “work around” with salvaged junk.  However, the result was a very usable ‘scope with particularly reliable triggering. 

By this time, I was 16 and being of a practical disposition, I left school to serve an apprenticeship in mechanical engineering trades, at the Royal Aircraft Establishment.  I opted for mechanical engineering since, at that time, I felt that pursuing a profession which was also my hobby was not a good idea. 

Other interests include playing classical piano, swimming, mountain hiking, cycling, motorcycles and steam locomotives.  I participated in the restoration to steam of  West Country Class Pacific, number 34105, ‘Swanage’.  Recently, I carried out a complete mechanical and cosmetic restoration of my 1980 Moto-Guzzi motorcycle. 

At the completion of my apprenticeship, I was retained at the RAE as a toolmaker, and within 3 months, promoted to the design drawing office at the National Gas Turbine Establishment.  During this period I completed the (British) Higher National Certificate in mechanical engineering, passing with distinction.  This included supplementary endorsements in mathematics and thermodynamics.  These qualifications are adjudged to be equivalent to a United States BS in Mechanical Engineering Technology. 

My professional life has been fairly varied with experience ranging from prototype manufacture and assembly to supervision of professional engineers.  I rapidly progressed from designer level to senior engineer, then section leader of the “stored energy systems” section at Graviner Ltd, England.  This involved design and development of small pneumatic pressure storage and release systems for infra-red night vision equipment cooling  and fin actuation of guided missiles.  The infra-red coolers employ nitrogen which is expanded through a Joule-Thompson cooler.  The fin actuation systems employ helium for the highest compressibility.  Helium storage pressures were up to 11500 psig (70°F) which is quite a challenge! 

Graviner was acquired by Williams Holdings who also bought Walter Kidde Aerospace (WKA) in the US.  If you have flown at all, then you will have been on aircraft protected by WKA fire protection systems.  I was brought over here as their “Manager of Conceptual Design” because of my experience with pressure vessels and valves including stress and fatigue analysis, also gas discharge pressure control dynamics analysis using Runge-Kutta techniques.  In addition, my practical aptitude was recognized.  Part of my responsibility at WKA includes the Model Shop.  My work has been a hectic blend of design, analysis, test, development, customer liaison and technical presentations.  The responsibilities included representing WKA at the International Halon Replacement Working Group coordinated by the FAA.  I was responsible for heading up the development of a minimum performance test standard for the lavatory trash receptacle fire extinguisher.  This standard has now been published and is the international benchmark for the application.  (This minimum performance standard was the first of 4 in progress actually completed and published.)

Additionally, I have conducted significant research into alternatives to Halon 1301 as a fire-extinguishing agent for aircraft.  I was the first to show how dry powder (sodium bicarbonate) can be used effectively to suppress incipient hydrocarbon explosions in cluttered 3 dimensional spaces, specifically, military aircraft Dry Bays.  This system actually out-performed Halon 1301 on a mass basis.  This work was reported in the June 1993 edition of Scientific American, by Mike Bennet and his team at Wright Patterson Airforce Base.  (Mike and his team provided the facility and protocol to test alternative extinguishing agents and systems.  I did the technology development  at WKA followed by performance testing at the Combustion Research Center of Fenwal, prior to the test series at WPAFB.  At that time, Fenwal were also owned by Williams Holdings.) 

A significant aspect of the investigation of fire extinguishing agents is faithful simulation of the fire and / or explosion conditions that are of concern.  To this end, I designed and supervised the construction of, an aircraft dry bay fire / explosion simulator.  This simulator employs a full-scale aluminum mock-up of the actual dry bay to be protected.  Simulation of environmental parameters includes external airflow over the “wound”, cooling down to -40°F of the structure and internal airflow and internal airdump due to rupture of bleed air ducts.  The explosion scenario is usually due to either or both rupture of a hydraulic line or ram pressurization of a fuel tank by the round resulting in fuel squirting back into the bay.  These are simulated using a pre-heated and pressurized bottle of diesel fuel which is ignited by an aluminum incendiary igniter to simulate the incendiary ignition source from a round.  This results in an oxygen limited fast growth fire.  The rate of growth (characterized by rate of pressure rise multiplied by the cube root of the volume in which the event takes place, typically expressed in bar.m/sec) is characteristic of a low-grade explosion.  The internal and external airflow, fuel, igniter and suppression events are controlled automatically by a programmable sequencer.  This simulator is the only one of its type existing that I am aware of, short of the various government facilities which use live rounds and cost approximately 5 times as much to operate.  The US Navy were the first to use the facility and they were impressed by the faithful simulation of environmental parameters and fire events. 

Since then, I have received a US patent (number 5660236) on a (proven) concept which uses a pyrotechnic gas generator to pressurize and heat the lower volatility “environmentally friendly” alternative extinguishing agents under consideration.  This technique involves raising the flash-vaporizing mass fraction of the expelled agent (sub 100msec discharge time-frame) to the same level as that exhibited by Halon 1301 at 70 °F as characterized by the Jacob number. 

I recently completed a new design of re-settable manual / electric powder discharge valve for military vehicle fire extinguishing.  This includes a novel safety device which automatically prevents recoil if an unmounted extinguisher is accidentally discharged.  (This actually happens, and it KILLS.)  I have received two US patents on this design, one describing the discharge valve (6032745) and another which describes the safety valve (6029947).

Lately, I have returned to my interests in classical piano and vacuum tube audio amplifiers.  I have designed and built from scratch, a pair of mono-block KT88 power amplifiers and a balanced pre-amplifier. The power amplifiers are extremely pleasing and have taken their place in my primary audio system.    The original design involved breadboard development of a wide-bandwidth differential cascode drive circuit and a reliable high-voltage (650V) regulator using semi-conductors. The balanced line stage which is of the transformer coupled push-pull type, is able to accept both balanced and unbalanced sources.  The line stage was designed and built specifically to complement the mono-block power amplifiers.

 Subsequently, I have developed and implemented a fairly original DC coupled cascaded differential drive circuit to replace the cascode.   The harmonic distortion of this circuit is notably low and is the same at both output terminals even when driven with an unbalanced source.  It is the only circuit of many which I investigated to exhibit this desirable characteristic.  While implementing this drive circuit, I took the opportunity to completely re-built the amplifiers to incorporate separate active vacuum tube voltage regulators for the output stage, the drive stage and the bias.  The regulators employ pentode series-pass tubes using well-filtered screen grid supplies to obtain high ripple rejection (circa 65dB) and cascode error amplifiers.  I developed a technique to apply ‘feed-forward’ to the cascode error amplifier to enhance the line regulation.  The amplifiers exhibit particularly excellent total / intermodulation distortion performance, frequency response, clarity and sound stage.  The sound with rock, choral and classical piano music is enlightening.  This is particularly pleasing since classical piano is one of my main areas of interest. 

More recent work includes an integrated stereo amplifier featuring “switchable-on-the-fly” triode / Ultra Linear modes of operation of EL34 power pentodes in push-pull.  The gain in the Ultra Linear mode is corrected (with respect to triode operation) by simultaneously introducing 3dB of global negative feedback when switching to this mode.  The amplifier also features a hybrid high voltage regulator.  The series pass element is a hexfet while the error amplifier is a EF86 low-noise pentode.  The error amplifier has a soft start feature to bring the high voltage supply on gently.  This amplifier includes a precision, low-noise RIAA phono pre-amplifier suitable for moving coil cartridges. 

More recently, I replaced the semi-conductor analogue signal electronics in my CD player with a pair of special-purpose step up transformers, connected in XLR (balanced) format to the 6SN7 push-pull balanced line-stage.  The resulting system is truly rewarding to listen to and a fabulous platform for performance standard reproduction of all types of music.   

A couple of side line projects came in at this point:  A small guitar practice amplifier with Baxandall tone controls and variable saturation distortion capability.  A jfet battery phono stage intended for LP to CD transcriptions.

I completed a very ambitious transformer-coupled single-ended 845 stereo amplifier.  I developed and wound my own wide-band double C core output transformers for this project.  This design turned out to be quite an advance on the push-pull amplifiers in terms of sound quality and is a delight.

To complement the 845, I designed and built a pair of two-way ported speakers.

On the vinyl front, I designed and built a phono stage which uses the Western electric 416 planar triode for the input stage.  I have now developed and built a Mk11 version of this which uses separate active tube shunt regulators for each stage.

Being a glutton for punishment, the 845 output transformer project was not enough so, I developed and wound a pair of output transformers for a 300B SE stereo amp.

To improve my system integration, I developed and built a line stage which removes the sub energy from the main channels and also buffers the lines to the sub woofers(s) from the main channels.  This unit greatly improved the imaging of my system and made it very easy to get the sub-bass sounding authentic.