I've just uploaded a pdf version of the HP 5090A Ops and Service manual to Didier's site at..... http://www.ko4bb.com For now at least it's also available at.... https://www.mediafire.com/?u0bf1eips89uo3h The 5090A was an HP product designed in the UK in the early 1960s and was an off air frequency standard intended for use with the BBC Droitwich broadcast service when it was broadcasting on 200KHz. If anyone has a copy of the 5090B manual they'd be willing to scan and share that would be very much appreciated, the A and B versions of the 5090 are quite different. Nigel GM8PZR