The Los Angeles and Orange County Audio Society site hosts an interesting paper describing a step by step procedure for upgrading the B77 and PR99 Revox models for higher playback quality. The document is a work by Arian Jansen of Sonorus Audio. We talked about Sonorus Audio’s
ATR10 tube reel to reel deck here.
The modified machine becomes a playback-only device, addressing hi-end hifi listening, however it is possible to preserve recording functionality by applying only part of the modifications.
The guide contains DIY instruction to perform:
- doubling operating speed up to 15 IPS, for lower speed models (US residents only, due to 60Hz power-supply requirement)
- conversion from NAB to IEC EQ
- upgrading the output capacitors to higher specs components
- removing from signal path the components (a couple of transistors) required for auto-muting, used to suppress audio output during ff/rew operations.