Thank you everyone. I have a few 1/2 inch master tapes for the Studer A820, as opposed to about 100 1/4 inch masters or dubs. This was Stewart's pride and joy - so I feel very honoured to be its guardian. This actual machine belonged to Simon Heyworth, who helped to set up Manor Studios for Branson; SH was the producer for Tubular Bells and he has mastered numerous albums and re-relaeses over the last 35 years.
The A820 has just come back from some repairs with blown Rifa caps in the AC suppressor circuit and motor controller boards. Simon Griffett at Audio Related in Bucks fixed this. SG looks after SH's machines, as well as AIR and EMI studios.
There's no point in copying from 15 IPS 1/4 inch to 1/2 inch. I will have to keep my eye out for other 1/2 inch tapes over time. They're a lot harder to come by.