Can Potentiometers Affect Your Electric Guitar’s Tone?

Even though typical electric guitar owners consider changing the stock pickups of their guitar as the most cost effective way to upgrade to a better tone, would changing the pots or potentiometers be the more cost-effective option? 

By: Ringo Bones 

Whenever they are dissatisfied with the sound of their electric guitar and they have some money burning a serious hole in their pocket, most electric guitar owners resort to upgrading the stock pickups of their electric guitars as a “cost effective way of upgrading their electric guitar sound. After all, there are well-reviewed DiMarzio humbuckers and Lace Sensor single-coil pickups that can be bought for less than 500-US dollars that would readily transform that 500-US dollar electric guitar given to you as a gift last Christmas into something that sounds similar to a one used by a famous rock guitar god. But what if I told you that there’s a far more cost effective – i.e. cheaper – alternative way to upgrade the existing tone of your electric guitar. 

Consider changing potentiometer values of your electric guitar, a reliable potentiometer brand often used by top electric guitar manufacturers like Fender or Gibson seldom sells more than 50-US dollars each. And if you’re soldering and electronic DIY skills are as good as your guitar playing, you could save a bundle in labor costs – given that they are relatively easy to install and swap around. From an electronic engineer’s perspective and from the electric guitarists “point-of-hearing”, volume pots or potentiometers act as a tone filter – given that a typical classic Fender Strat or Gibson Les Paul uses internal shielded / Faraday caged wiring  to connect its pickups with the output socket via wires with a 30 picofarad per foot capacitance ala JAN (joint Army-Navy) RG-58 shielded cables. The higher the potentiometer’s value, the more treble you hear. With a little DIY experimenting, you might find out that your electric guitar’s stock pickups can be made to sound like the one used by Eric Clapton during his Cream days just by swapping the pots and a few minutes worth of DIY soldering. 

When it comes to single-coil pickups, stock Fender Stratocaster / Telecaster guitars or Fender type clone electric guitars that use single-coil pickups typically use 250-kiloohm (250-K) potentiometers, substituting it with a 500-K potentiometer will brighten single-coils, whether they are of Stratocaster-style lipstick or the much older soapbar (pre 1955 era) style pickups. For an airy sounding Strat, try a 1-megaohm (1-Meg) potentiometer. The trick here is to find a value that provides clarity of tone without introducing too much harshness or noise.    

When it comes to humbucker pickup use and installation, most manufacturers follow Gibson’s lead and use 500-Kiloohm (500-K) potentiometers for humbucker pickups. If your humbucker pickup equipped electric guitar sound too bright, too shrill or too tonally thin, try mellowing its tone by changing to a lower value potentiometer – typically 300-K or 250-K. Conversely, you can add more presence to a humbucker by switching to a 1-Meg volume control. Just remember that in a dual-volume Les Paul style rig, you can mix volume controls say like brightening only the neck pickup or darkening the bridge pickup of your Les Paul type electric guitar for greater tonal flexibility usually very useful for country music or old school electric Blues styles. 

Weak 9 Volt Batteries: Secret to a Great Fuzz Pedal Tone?

Even though batteries for wireless units and guitar tuners should always put-out full 9-volts when tested on a voltmeter, can weak 9-volt batteries in your Fuzz or distortion stompbox give you great tone?

By: Ringo Bones 

I might be the last person to know about this electric guitar “tone tweaking” trick during my amateur metal band days back in the late 1980s, but it has been empirically proven by guitar gods and guitar techs since the days of Woodstock that a weak 9-volt battery that only puts out between 5.5 to 7.5 volts when connected to a voltmeter can actually result in a pleasing tone when used to power your Fuzz or other distortion type stompbox effect pedal. Famed guitar legend Duane Allman reportedly preferred weak batteries in his Dallas Arbiter Fuzz Face, though any voltage reading lower than 5.5-volts – and depending whether your distortion pedal is IC op-amp or germanium transistor based – it could be the difference between “death metal tones” to a dead as a doornail silent stompbox. But why do weak 9-volt or PP-3 batteries produce a pleasing tone when used to power your Fuzz Face / distortion type stompbox effects pedals?  

The “subjectively pleasing tone” one gets when using weak 9-volt PP-3 batteries on their distortion pedals is probably a holdover from the days before the invention of more efficient solid-state silicon rectifiers. Where electric guitar tube amplifiers still use vacuum tube power supply rectifier and / or selenium rectifier based power supplies when a hard-struck power chord usually causes power supply voltage sag and the accompanying warm fuzzy distortion tone – and unlike your typical hi-fi vacuum tube amplifier, this “fuzz tone” is usually in the 200 to 300 percent total harmonic distortion range. Though there are some electric guitar vacuum tube amplifiers like use both vacuum tube and solid-state rectifiers – Mesa Boogie for example – for reasons of tone. This makes the GZ34 vacuum tube rectifiers, especially the NOS Mullard types, are now highly sought after by vintage guitar amp enthusiasts. If only Mullard made reliable versions of those pesky selenium rectifiers used in the Fisher 500 C Receiver. 

 

The 7591 Vacuum Tube: The Jazz Guitarists' Vacuum Tube?

Even though it was the preferred vacuum tube for Jazz guitarists near the end of the 1960s due to its use in the 1966 Ampeg GS-12R guitar amp, is the 7591 vacuum tube deserve the acclaim as the Jazz guitarists’ vacuum tube? 

By: Ringo Bones 

Sometimes I wonder whatever compelled the Russian vacuum tube manufacturer Sovtek – via their Electro Harmonix arm – to remanufacture the 7591 pentode output power vacuum tube during the first few years of the 21^st Century given that it became virtually extinct around the time when Ronald Reagan ruled the free world. Was the Fisher 500-C and Hermon Hosmer Scott’s receivers a runaway success during the height of the Cold War? Or was it that the 1966 Ampeg GS-12R amp, oft used by Jazz guitarist on this side of the Iron Curtain near the end of the 1960s, was also a runaway success for “underground” Jazz guitarists in the then Soviet Union and the rest of the then Eastern Block countries? Anyway, both guitarists and hi-fi enthusiasts are very eternally grateful for Sovtek / Electro Harmonix for remanufacturing the 7591 vacuum tube – not just for the still functioning 1966 Ampeg GS-12R amps the world over but also the still working Fisher and Scott receivers needing fresh 7591 vacuum tubes around the world. 

The 7591 gained credence as the “Jazz guitarists’ preferred vacuum tube” probably around the time of the Reagan presidency where NOS and even (gasp!!!) used but still functional 7591 vacuum tubes were desperately scrounged by discriminating Jazz guitarists and owners of Fisher and Scott receivers in desperate need of fresh – or at least working - 7591 tubes. And the 1966 Ampeg GS-12 guitar amp gained a reputation as a clean Jazz guitarists’ amp when it was introduced in the late 1960s even though it can rock when pressed. 

During the virtual extinction of the 7591 vacuum tube in the middle of the 1980s, many 1966 Ampeg GS-12 guitar amp owners – as well as Fisher and HH Scott receiver owners were experimenting ways to shoehorn the 6V6 vacuum tube – in the Ampeg – and the 6L6 vacuum tube – in the Fisher and Scott receivers with various degree of success. It might have involved serious “brain surgery” in rearranging the wiring and the biasing resistors and coupling capacitors of their Ampeg amps and Fisher and Scott receivers since the 6V6 and 6L6 vacuum tubes are beam tetrodes while the 7591 tube is a pentode. Though 6V6 vacuum tubes that had been “successfully” transplanted into a 1966 Ampeg GS-12R guitar amp did manage to produce a very interesting tone that make them now highly collectible, sadly, less skilled thermionic electronic tinkerers irreparably damaged their Ampegs in such endeavors. 

Historically, the 7591 pentode output vacuum tube was introduced in 1958 and registered with the EIA in 1960 via Westinghouse’s receiving tube factory in Bath, New York. Given that Dr. Harvey C. Rentschler used to be the director of research for the Westinghouse Lamp Division, every vacuum tube enthusiast is now wondering how instrumental Dr. Rentschler was in the development of the famed 7591 pentode output vacuum tube. And by the way, the 1962 Westinghouse 7591 vacuum tube is the best NOS type for this kind of tube.         

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. 

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.