The story of the Sola Sound Tone Bender is entwined with the the Arbiter Fuzz Face, the Vox Distortion Booster, and the Vox Tone Bender. The original Fuzz Face schematic is identical to the earlier Sola Sound Tone Bender so-called "Mk 1.5" by fuzz historians. The design for both pedals is claimed by Gary Hurst, though doubt over the Mk 1.5 persists due to conflicting evidence from interviews given by Hurst and Dick Denney (Vox engineer).
The Designer, Gary Hurst, and his controversial tale...
Gary worked for JMI/Vox in the early 1960s before setting up shop in London as an independent electronics guy by the mid 1960s.
Gary's independent business included designing a pedal called the "Tone Bender" for the Musical Exchange music shop. The Musical Exchange used the name "Sola Sound" for their electronics. The relationship between the Musical Exchange and JMI/Vox isn't completely clear, but the owners of the shop were also former JMI employees and they seemed to share product lines across the JMI/Vox store and the Musical Exchange.
Modifying the Maestro Fuzz Tone for more sustain...
It is often reported that Vic Flick brought his Maestro Fuzz Tone to the Musical Exchange for service to being the Tone Bender development, although other sources believe the guitarist was actually "Big" Jim Sullivan. Whoever it was, someone requested more sustain from the rather percussive Maestro unit. The technician who improved the Fuzz Tone was Gary Hurst. Following this, either Hurst or the Musical Exchange decided to sell the improved Fuzz Tone as their own product called the Tone Bender.
Gary's first Tone Benders, now referred to as version "Mk I", are modified Maestro Fuzz Tones. The very first versions were housed in a distinct wooden box. Due to few being produced, and the delicate wood enclosure, the wooden boxes are very rare.
Mysterious and controversial second version...
A second version, referred to in retrospect as the Mk I.V, or 1.5, contains a two transistor circuit identical to the later Arbiter Fuzz Face, and remarkably similar to the nearly simultaneously released Vox Distortion Booster. When the first "pedal histories" were being written, Hurst denied the existence of a two transistor Tone Bender. He later recanted his initial denials and claimed the two transistor design as his own.
It is possible that the Mk I.V wasn't even sold at the Musical Exchange, but the JMI/Vox store, according to one owner's account.
This two transistor circuit appeared in numerous designs from English companies, therefore I have dubbed the two transistor circuit the 2 Transistor English Fuzz to cover all the numerous effects with this similar circuit.
The JMI/Vox connections...
Gary's earlier JMI/Vox employment haunts him regarding the two transistor circuit because it is featured on the prior released Vox T.60 amp. Gary worked under lead Vox Engineer Dick Denney, who designed the AC series of Vox tube amps, and was known to dabble in distortion designs that were not allowed to be developed under JMI owner Tom Jennings. It isn't documented what circuits Dick may have tinkered with or even shown to Gary, but it is often speculated that Gary may have taken something away from Dick. Gary denies Dick Denney had anything to do with the Sola Sound Tone Bender or Arbiter Fuzz Face. To be fair, we could easily speculate it was the other way around, that Denney took from Hurst's original ideas. Denney was featured on TV, in books, interviewed, and revered for designing the Vox AC line of amps, so perhaps there is an unfair bias in favor of him due to celebrity, whereas Hurst was relatively unknown until the internet age.
The Vox Tone Bender, released after Hurst's designs, contains the two transistor fuzz with different component values, and is credited to Denney.
A third version named the Mk II...
The Tone Bender soon returned to a three transistor variation known as the Mk II Professional. This can be found in Sola Sound and Vox brand enclosures. The JMI/Vox store wanted to carry the fuzz that the Musical Exchange had.
Reusing the Mk I...
Around the same time Sola Sound got a Mk II, the Marshall Supa Fuzz appeared. This was another Hurst design that rehashed the Mk I (Fuzz Tone) design.
Reusing the Mk I.V...
The Arbiter Fuzz Face was a product made for the Sound City music store. Sound City was owned by Ivor Arbiter, and he chose his own last name to brand Sound City's line of electronics.
I've never read an account of Arbiter actually hiring Hurst to design the Fuzz Face, but Hurst claims the design. Arbiter or an associate could have hired Hurst in the same way Macari's had hired Hurst earlier.
Later Tone Benders
Mk III and Mk IV Tone Benders feature a different fuzz circuit and a tone control. The tone control requires a third knob which easily distinguishes these versions from the early ones.
These models use a Darlington pair as an input amplifier into a No Bias type germanium fuzz stage, followed by a passive tone network.
Supa and Jumbo Tone Benders are copies of the Electro Harmonix Big Muff Pi. They are a distinct variation as they leave out the clipping diodes in one of the gain stages, and some appear to leave out the final make up gain stage as well.