Question
hi wayne , i have a small collection of orchids ranging from aspasia , epidendrum stanhopea dockrillia dendrockilum maxillaria pholidota and others but these in particular have been dropping all their leaves and bulbs or rhizomes have been shrivellin. Only changes have been the weather, very cold some nights and a hit of osmacote about 4 weeks ago. (although i noticed it didnt have the plastic coating on it)

Answer
All of the species you referenced have two things in common: they are plicate (ie thin) leaved and they are warm growers.  Since osmocote is a very slow release fertilizer, I don't suspect it as the problem.  Colder temperatures, especially if combined with keeping them slightly on the wet side, could have begun the process of root rot.  Leaf drop could have been initiated by the colder temperatures and shriveled pseudobulbs reflect the start of root problems.  I suggest you remove the plants from their pots and check the roots removing any roots that are mushy or in bad shape.  Then repot the plants in fresh potting mix. Most important is to move them to a warmer environment.  When new growth begins, gradually increase the light level (you didn't mention your lighting conditions).