Question: In which year, was this English rock band formed in Hertford that the lead vocalist Ian Gillan of Sabbath is best known for collaborating with?

Context articles: Episode Six
Born Again (Black Sabbath album)
Gillan (band)
Deep Purple
The Best of Black Sabbath
Born Again Tour 1983
Ian Gillan Band
List of Deep Purple band members
Ray Fenwick
The Javelins

Episode Six were an English rock band formed in Harrow, London in 1965.
 The band did not have commercial success in the U.K, releasing nine singles that all failed to chart, but they did find minor success in Beirut at the time.
 Group members Ian Gillan and Roger Glover left in 1969 to join Deep Purple, while drummer Mick Underwood founded Quatermass and later collaborated with Gillan.
Born Again is the eleventh studio album by English heavy metal band Black Sabbath, released in August 1983.
 It is the only album the group recorded with lead vocalist Ian Gillan, best known for his work with Deep Purple.
 It was also the last Black Sabbath album for nine years to feature original bassist Geezer Butler, and drummer Bill Ward, until he played the studio tracks on their 1998 live album "Reunion".
 The album has received mixed to negative reviews from critics, but it was a commercial success upon its 1983 release, reaching No. 4 in the UK charts.
 The album also hit the top 40 in the United States.
Gillan was a rock band formed in 1978 by Deep Purple vocalist Ian Gillan.
 Gillan was one of the hard rock bands to make a significant impact and commercial success in the United Kingdom during the early 1980s, with 5 albums in the Top 20.
Deep Purple are an English rock band formed in Hertford in 1968.
 The band is considered to be among the pioneers of heavy metal and modern hard rock, although their musical approach changed over the years.
 Originally formed as a progressive rock band, the band shifted to a heavier sound in 1970.
 Deep Purple, together with Led Zeppelin and Black Sabbath, have been referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies".
 They were listed in the 1975 "Guinness Book of World Records" as "the globe's loudest band" for a 1972 concert at London's Rainbow Theatre, and have sold over 100 million albums worldwide.
The Best of Black Sabbath is a double CD compilation album by Black Sabbath released in 2000 on the Sanctuary Records label.
 Its 32 songs are presented chronologically from the band's first 11 albums, spanning the years 1970 to 1983.
 Black Sabbath's classic six-album run, from 1970s debut "Black Sabbath" through 1975's "Sabotage" is celebrated with three to six songs from each album.
 Original vocalist Ozzy Osbourne's subsequent final two albums with the band, 1976's "Technical Ecstasy" and 1978's "Never Say Die!
", are represented by one and two songs, respectively.
 Replacement Ronnie James Dio's early 80's stint fronting the band on two albums is acknowledged with the title track of 1980's "Heaven and Hell" and a track from 1981's "The Mob Rules".
 The compilation closes with a song from 1983's attempted rebirth, "Born Again", former Deep Purple vocalist Ian Gillan's sole album with the band.
 "The Best of Black Sabbath" does not include any later material with vocalists Glenn Hughes (1986's "Seventh Star"), Tony Martin (1986–96) or the returning Dio (1992's "Dehumanizer").
The Born Again Tour 1983 was a global concert tour by in support of Black Sabbath's "Born Again" album.
 Both the album and the tour were the only ones of Black Sabbath's to feature former Deep Purple frontman Ian Gillan on lead vocals.
 Ex-Electric Light Orchestra drummer Bev Bevan was hired to replace Bill Ward, who had returned to the band for the recording of the album after a two-year hiatus, for the tour.
 This was the final tour to feature original Black Sabbath bassist Geezer Butler until 1992's "Dehumanizer" tour.
The Ian Gillan Band were an English jazz-rock fusion band formed by Deep Purple singer Ian Gillan in 1975.
Deep Purple are an English hard rock band from Hertford, Hertfordshire.
 Originally known as Roundabout, the group formed in March 1968 featuring vocalist Rod Evans, guitarist Ritchie Blackmore, bassist Nick Simper, drummer Ian Paice and keyboardist Jon Lord.
 This first lineup of the band, known as Mark I, released three albums within the space of a year – "Shades of Deep Purple", "The Book of Taliesyn" and "Deep Purple" – before Evans and Simper were fired from the band at the request of Blackmore and Lord.
 Mark II of Deep Purple saw Ian Gillan and Roger Glover replace Evans and Simper, respectively, in the summer of 1969.
 This lineup of the band has since been identified as their most successful, with their next four albums reaching the top four of the UK Albums Chart, including number-one albums "Fireball" and "Machine Head".
Raymond John Fenwick (born 18 July 1946) is an English guitarist and session musician, best known for replacing Steve Howe in The Syndicats, and as the lead guitarist of Ian Gillan's post Deep Purple solo project, the Ian Gillan Band.
The Javelins, sometimes also known as Ian Gillan & the Javelins, was a 1960s band fronted by Ian Gillan of Deep Purple.
 The band played live but never recorded in their initial spell together.
 The other members included rhythm guitarist Tony Tacon, bass player Tony Whitfield,drummer Keith Roach and lead guitarist Gordon Fairminer.
 All from Hayes/Heston area of West London.