PDP-8/E H724 power supply and serial interface

Pete Turnbull pete at dunnington.plus.com
Mon Nov 17 11:23:47 CST 2008

I've taken my newly-acquired PDP-8/E apart to clean out the dust and 
disintegrated foam, but I've not powered it up yet.  (In fact it's still 
in pieces while I sort out the foam).  I'll be checking the capacitors 
before I go much further.

Part of the reason for not powering it up is that it's a 110V version, 
and here in the UK my mains is 240V.  Looking at the engineering 
drawings (on David Gesswein's site, and Highgate) for the H724 (110V) 
and H724A (240V) supplies, I see transformer taps shown for both 
voltages, and on the face of it, it should be very easy to convert. 
Just a matter of moving the connections from tags 6 and 9 of the relay 
(or "realy" as the schematic calls it :-))  Has anyone ever done this?

Another question:  There are four 1N4721 rectifier diodes used for the 
+8V and +15V supplies (two pairs for two full-wave rectified supplies). 
  Someone before me has disconnected one end of one of them.  Usually 
that's because it's gone short, but my meter says this one is OK.  Any 
ideas why?

I'm also lacking any serial interface for this machine.  I do have some 
other spare boards; is anyone (especially in the UK) interested in a trade?


Pete						Peter Turnbull
						Network Manager
						University of York

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