Wednesday, July 31, 2013

Leslie Organ Speaker: The Ultimate Electric Guitar Speaker?

Even though the product is primarily intended to be used in early electric church organs, is the Leslie Organ Speaker the ultimate electric guitar speaker?

By: Ringo Bones 

Maybe it is its built-in paper coned woofer that is the primary reason for its sweet as honey sounds, or the rotating horn being rotated by a surprisingly silent motor system, or maybe the built-in vacuum tube based amplifier – which resembles like either a Leak TL12 Point One or a Quad II – that makes it the ultimate electric guitar speaker and amplifier. Either way, why can’t today’s electric guitar amplifier / speaker manufacturers offer something similar or even something better than the original Leslie Organ Speaker?
The often used model of the Leslie Organ Speaker by electric guitar players is the Leslie Model 145 Organ Speaker. It was used as a recording session electric guitar amplifier when the late guitar legend Jimi Hendrix recorded the studio version of Little Wing during the late 1960s. And despite his preference of using Fender guitars an Marshall amplifiers during his live performances, Jimi Hendrix prefer to use low-powered 1950s era Fender tweed amplifiers connected to dual cone / whizzer cone equipped 15-inch musical instrument speakers and Mosrite electric guitars with Bigsby tremolo bars. 

All guitarists have the US Navy researcher Donald Leslie (any relation to John Leslie?) to be eternally grateful to because it was he who designed the first generation of Leslie Organ Speakers equipped with a silent motor system to rotate the middle frequency-high frequency horn speaker to make its sound to fill a rather large church space despite its built in vacuum tube based amplifier is only capable of producing 12 watts or so. The good thing about the Leslie Model 145 Organ Speaker is that its built in vacuum tube amplifier can easily be modified – with just as easily as equipping it with a ¼-inch electric guitar input jack – to be able to accept and play an electric guitar. And by the way, other famous legendary guitarists who use the Leslie Organ Speakers when playing and recording electric guitar were Stevie Ray Vaughan and Pink Floyd’s David Gilmour.  

Even though there are digital guitar effects processors today that allow you to be able to replicate the sound of a classic Leslie Organ Speaker, they usually fall short in replicating the sweetness and the sound-staging capabilities of the real thing – like the iconic Leslie Model 145 Organ Speaker if one wants to mimic Hendrix’s Little Wing riff as he originally recorded it. Sadly, most Leslie Organ Speakers – especially the Leslie Model 145 Organ Speaker – is too low powered sound wise to be used in live stadium rock settings.

As a “solution” to the Leslie Organ Speaker’s inability to play loud enough in stadium rock concert settings, Pink Floyd guitarist David Gilmour tried using Maestro Rover units. Even though they are clearly much louder than the Leslies in studio recording session settings, the Maestro Rover revolving / rotating full range electric guitar speakers were still deemed not loud enough for stadium rock concert application settings. Then Phil Taylor and Paul Leader designed something that provided Gilmour with that distinctive “Leslie” effect that was adequately loud enough for stadium rock concert use – thus the Doppolas were born.  The Doppolas are rotating speakers - la Leslie Model 145 Organ Speaker - except that the Doppolas are equipped with two six inch 100-watt drivers making them loud enough for live stadium rock concert use. Looks like today’s digital audio processing modeling technology for electric guitar effects processing use is still not advanced enough to replicate that rotating and whooshing Leslie Organ Speaker tone. 

Sunday, July 7, 2013

Can Nuvistors Be Used As An Electric Guitar Preamplifier?

Even though they are for all intents and purposes just ultra small vacuum tubes that were discontinued back in the late 1971, why do electric guitar preamplifier manufacturers never made one using nuvistors? 

By: Ringo Bones 

Even though nuvistors were briefly reintroduced back into the consumer electronic marketplace when Musical Fidelity CEO and Classically trained clarinetists Antony Michaelson released the Nu-Vista Pre-Amplifier back in August 1998 and the Nu-Vista 300 hybrid power amplifier before Michaelson got too busy playing with the Michelangelo Chamber Orchestra while being recorded by Tony Faulkner, these ultra-miniature vacuum tubes were sadly largely discontinued when the 1970s rolled around. It was largely Michaelson’s fortunate bulk-purchase of a stash of unused Mullard 6CW4 high-mu triode nuvistors that somewhat saved the largely forgotten electronic devices from total obscurity. 

Nuvistors are a type of miniature vacuum tube introduced by RCA into the world’s consumer electronic markets back in 1959 though Mullard also produced it under license from RCA during the 1960s. The technology behind nuvisors became possible after the 8-year long research of Dr. Harvey C. Rentschler allowed him to conclude that atoms of gas – like oxygen, hydrogen or nitrogen – actually dissolve in the crystalline structure of some metals just as salt dissolves in water. These gas particles “loosen” the electrons in this structure, causing them to be emitted from the metal more readily as heat is applied. Dr. Rentschler’s findings were later published in the July 1943 issue of the Scientific American magazine. And such phenomena lead to the development of smaller and more efficient vacuum tubes that eventually lead to the development of the nuvistor. 

Nuvistors are thimble shaped but are actually 5 to 10 times smaller than an actual thimble and much smaller than conventional preamplifier vacuum tubes that were manufactured after World War II. Nuvistor triodes and a few tetrode types were made. The newfangled ultra-miniature vacuum tubes were made entirely of metal and ceramic. 

During its heyday, manufacturing nuvistors require special equipment since there is no intubation system to pump gases out of its ultra miniature metal envelope. Instead, the entire structure is assembled, inserted into its metal envelope, sealed and processed in a large vacuum chamber with simple robotic devices. Even though the “vacuum” inside a typical thermionic vacuum tube is 50,000 times less rarefied than the Horsehead Nebula, the vacuum chamber used to mass produce nuvistors must have been a technological manufacturing tour-de-force of its day to be able to maintain a “vacuum” of about 0.000001 Torr or millimeters of mercury – a level required for a high quality consumer electronics grade vacuum tube. By way of comparison, normal atmospheric pressure at sea level is 760 Torr or 760 millimeters of mercury. 

One of the most popular types of nuvistor during the electronic device’s heyday was the RCA 6DS4 Nuvistor triode vacuum tube. It measures 20-mm high and 11-mm in diameter. During much of the 1960s, nuvistors were among the highest performing small-signal receiving tube. They feature excellent VHF and UHF performance plus lower noise figures than early point-contact germanium transistors. Nuvistors are widely used throughout the 1960s in television sets beginning with RCA’s “New Vista” line of color TV sets in 1961 with the CTC-11 chassis and top-of-the-line radio and high fidelity equipment’s RF sections. Nuvistors competed with the solid-state revolution of the 1960s along with General Electric’s Compactron and probably held it at bay for a few years. RCA discontinued the use of nuvistors in their television tuners by late 1971. 

One famed application of nuvistors during the electronic device’s heyday was in the Ampex MR-70 open reel tape recorder for studio use – it was a costly studio tape recorder whose entire electronics section was based on nuvistors. Another application of the very small nuvistor vacuum tube was in the studio-grade microphone of the 1960s – the famed AKG / Norelco C12a, which employed the 7586 medium-mu triode nuvistor – the first nuvistor released on the market. It was later found out that with minor circuit modifications, nuvistors could sufficiently serve as an “ad-hoc” replacement of the then obsolete and no longer produced in the 1960s Telefunken VF14 tube used in the famed Neumann U47 studio microphone.
Given that the “roadie / guitar tech” who first made those fuzz-boxes / stomp boxes for the famed 1960s guitar-god Jimi Hendrix used to be Jimi’s regular TV repairman, it is quite a mystery why no examples of do-it-yourself nuvistor based electric guitar preamplifiers or effects / fuzz boxes are in existence. The famed Dallas Arbiter Fuzz Pedal used 1960s era germanium small signal transistors – imagine if some enterprising TV repairman familiar with the working of nuvistors experimented replacing the early germanium trannies with one. 

Technically, nuvistors can operate up to 110 volts DC and as low as 30 volts DC so powering one with a 9-volt PP-3 could be an engineering challenge back in the 1960s, though today’s high-voltage lithium polymer batteries used in Airsoft gaming applications could easily supply the 30-volt DC anode voltage required for nuvistor fuzz pedal operation. A typical nuvistor has an amplification factor or mu of 64 – comparable to the 12AX7 preamp tube’s 100, but  nuvistors have a much stronger transconductance or gm compared to the 12AX7 preamp tube. So if today’s top Russian vacuum tube manufacturers like Svetlana or Sovtek / Electro Harmonix  or those in Mainland China decides to remanufacture nuvistors, it would probably end up as electric guitar preamplifiers and fuzz / distortion effects pedals and boxes.