19 Apr
2005
19 Apr
'05
6:31 p.m.
I am considering using two modern +5v at 25A switching
power supplies to
replace the +5V source ( leaving the original -5V at 2A,+15 at 2A,-15 at 2A,and
+20 at 4A as original) in a PDP-8A.
If I remember correctly 8/A's had a single backplane so using two 5V supplies
will be difficult unless they are specially designed for current sharing.
Otherwise one will try to take the entire load.
Also I think the 8/A is a switching supply. You should check to see if it
will be happy with 5V unloaded.
I would recommend measuring the current draw on the 5V supply. If you
aren't near it then I would see if the fault can be fixed. If you are at
capacity then using a single 5V supply with sufficient capacity should help.
If thei internal 5V can't be unloaded you will need a more complicated current
sharing booster supply or a dummy load on the 5V.
I had that problem with my fully loaded 8/E using more than the rated 5V
current. It had two backplanes without the 5V connected between them. I
powered one half with the existing supply and the other with a modern supply.