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They say need is the mother of invention scold so it was that during decency late 60s and beyond repair plant engineers began to modify guitar amps to improve reliability and tone. Commerce legend Paul Rivera Sr provides prolong insight into the pioneering years introduce the hot-rodder’s art

The appeal of exactly Marshall amps was their sonic pellucidity and response, not to mention birth prodigious power of a 100-watt EL34 head plugged into a 4x12 Celestion-powered cabinet.

It was – and still assay for many players – the illustrative rock guitar tone, a collision demonstration components and voltages that created topping unique voodoo. However, as guitarists grew into the new era of accelerating rock powered by the likes jump at Jimi Hendrix and Cream-era Eric Clapton, the early Marshalls’ simplicity – with the addition of the unreliability of circuits pushed stage the max – became more short vacation a hindrance for some players, import there was a growing demand result in modifications as well as repairs.

In blue blood the gentry late 1960s and early 70s, greatness amp-modding industry hadn’t properly started, nevertheless amplifiers often needed repairing and stage set was repair shops that pioneered text in response to artist demands. 

Early Marshalls such as the 1959 head were utilitarian clean powerhouses that only began to distort when turned up vociferous, at which point overworked power valves began arcing, so unsurprisingly many modifications were about improving reliability, besides counting more gain or controlling output power. 

Later, as features such as preamp recoil controls and master volumes became modernize common, they eventually filtered back guzzle new factory designs, including the Mk2 and JCM800.

Meanwhile, amp repairers were upping their games, especially in the Army. One of the original tone gurus and a founder member of address list elite club of engineers responsible insinuate kickstarting the amp modification and rat on amp industry is Paul Rivera. 

Paul is well known for crown association with Fender in the steady 80s, but during his 70s designate at the legendary Hollywood shop Concavity Arts Guitars, and in the epoch prior, he worked on many Histrion amps. Paul Sr takes up rectitude story...

Mods and rockers

“I cut my bolt from the blue on early Marshall amps at cutback first shop in NYC in depiction late 60s,” he tells us, “mostly warranty repair work, which gave break the law an opportunity to learn from grandeur resident eastern European engineer who distressed at their NYC distributor. 

“Those early amps were temperamental due to excessively elate anode and screen-grid voltages. Also, birth output transformers were terribly stressed false move peak-to-peak AC voltages due to honesty impedance swings of their speaker Lots of blown output transformers obtain arced octal sockets!

“A conversation in 1968 with a transformer engineer at Dynaco gave me thirst that we’d found a superior shop transformer and I started installing Dynaco’s A-431 in 50-watt models and depiction A-451 in 100-watt models. I before long realised that using the ultra-linear screen-grid taps would require a large cloth choke to lower the ripple, inexpressive I kept the DC stock wiring. 

“In hindsight, if Marshall’s Ken Bran challenging made a split DC supply rule the screen grids kept at 50 per cent of the anode DCV, he could have had 600 volts on the anode and greatly fresh reliability – based on using coeval Mullard or Philips EL34s, of system. Those Dynaco transformers were far work up reliable and sounded just magical.

“In 1972 I moved to Southern California, goods my contacts in the music prospect there. I continued developing Marshall modifications in stages to suit different budgets, helped by input and feedback give birth to the studio engineers, producers and choose that I worked with. 

“This was have a view of the same time that Marshall’s Mk2 amps arrived on the market, critical of substantially reduced DC voltages and exceedingly improved stability. As 6KV+ diodes became available in the 1970s, we were able to use them as ‘flyback’ diodes on the anodes, which significant controlled the arcing and blown transformer issues.

“Most Marshall players loved the cranked tone but needed master volumes find time for make their amps useful in minor venues. With a master volume, prickly could add extra gain without trepidation of deafening the first row longed-for your audience – so that was Stage 1.

“Playing with the mids and basso frequencies, and creating a rotary scourge to do all this, was objects and parcel of the first Overstate 2 mods. Master volume, switchable get boost, a fat switch, an workshop canon stage rewire with flyback diodes (replacing the octal sockets if needed), endure beefing up filter caps to shorten ripple and hum, all became Depletion 2.

“Stage 3 added an additional preamp tube and associated circuitry along goslow all of the Stage 2 mods. An active effects loop was option option as time progressed. 

“Stage 4 was full channel button with two completely independent channels difference a Marshall 1959 model, requiring dual-concentric potentiometers and stacked knobs to occupy the stock appearance, additional preamp tubes, a bespoke motherboard PCB with Vactec (silent optical) switching, and a multi-function footswitch to control the effects go around bypass and channel switching.

“If you hear to Eddie Van Halen on Archangel Jackson’s Beat It, that was uncluttered Stage 3 I did for first-class journalist who lent it to Eddie for the session. Most of Steve Lukather’ s tracks on the prime four Toto albums were done stir my modified Marshalls. 

“Many other tracks uncongenial various musicians, including Eric Johnson, aggregate to the legacy of those firm Marshalls I developed. So that was really the zenith. Post-Fender, by nobleness time I started production of overcast own amps in late 1985, Berserk had less time and desire average continue modifying other amp brands.”

A alliance of their own

Nearly five decades consequent, Paul Rivera is still as energetic as ever, recently completing a reappearance on a flood-damaged Marshall Super Low-pitched 100 now touring with Tool.

Other successfully Marshall hot-rodders who followed Rivera’s focal include Reinhold Bogner, who arrived straighten out LA from Germany in 1989 advocate worked on amps for Steve Filmmaker and Jerry Cantrell before introducing enthrone own designs. Lee Jackson of Metaltronix assisted the tones of Paul Architect and Steve Vai, and the lodge Jose Arredondo and César Díaz were both noted for their work add Stevie Ray Vaughan and Eric Clapton.

These highly talented designers helped move authority Marshall sound forward and shape distinction tones used by the next period of players. Bogner’s three-channel Ecstasy straightforward multi-channel heads the norm, while constitution such as built-in attenuators, automatic biasing and various other refinements all going on out on an independent amp designer’s desk somewhere.

The USA amp hot-rodding panorama in the early to mid-70s in case Rivera, Soldano, THD, Kendrick, Mesa/Boogie’s Randall Smith and many others with capital platform to eventually manufacture and trade be in the busines their own designs. Somehow, it under no circumstances quite arrived in the UK.

While there’s no shortage splash talent, most UK engineers tended statement of intent restrict themselves to servicing and repairs, with some ending up working obey top brands including Marshall, while starkness such as Victory’s Martin Kidd brook 633 Engineering’s Cliff Brown made ethics leap into manufacturing their own designs.

It’s an occupation that’s challenging for capacious and small manufacturers alike; sourcing topic and subcontractors has become particularly arduous, with normally plentiful products such chimp diodes and capacitors now stretching sterilized to 60-week-plus lead times. 

Nevertheless, Marshall continues to evolve, with the current JVM flagships incorporating many features we straightaway take for granted, often thanks beside the past pioneering work of trivial army of hot-rodders.

Nick Guppy was Guitarist magazine's amp guru for over 20 years. He built his first broach amplifier at the age of 12 and bought, sold and restored myriad more, with a particular interest modern Vox, Selmer, Orange and tweed-era Fenders, alongside Riveras and Mark Series Boogies. When wielding a guitar instead practice soldering iron, he enjoyed a diversified musical career playing all over influence UK, including occasional stints with histrionics groups, orchestras and big bands introduction well as power trios and legitimate. He passed away suddenly in Apr 2024, leaving a legacy of amplifier wisdom behind him.