Date   : Tue, 11 Dec 2007 09:18:25 +0000
From   : pete@... (Pete Turnbull)
Subject: Black power supply

On 08/12/2007 14:35, Andrew Benham wrote:
> Paul J wrote:
> 
>> Could anyone shed any light on the black power supplys, how long they were
>> used for, were they replaced in machines because of problems, anything
>> related to the history.
> 
> My recollection was that the black power supplies were linear, rather
> than switched-mode, and although weren't subject to a 'recall' were
> always replaced on sight.

They are linear, and there are three different models, of varying 
degrees of goodness (or badness).  Two gloss black and one matt black 
(or maybe the other way around), all with black moulded power cables. 
They were used on early model Beebs (mostly Model As), before the 
switchmode units were available.

They weren't officially "replaced on sight" but there were several good 
reasons to swap them for the metallic switch-mode units.  For example, 
one of the three varieties was unofficially known as the "adapter and 
exploder" (a variation on its real name) because it had a tendency to 
overheat on an expanded machine and fail, sometimes loudly -- and these 
were often replaced without argument.  None of the three linears had an 
auxiliary power connector, so they were no use for disk drives, and most 
didn't have the capacity to handle an expanded machine.  Therefore, one 
of the reasons to replace them was fitting a disk interface; another was 
fitting a second processor.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York