substituting 7401 for 8881 in a PDP-8/E

My PDP-8/E stopped working at the weekend, which is a bit of a nuisance as I need it working for the DEC Legacy event at Windermere in October -- and I'm going on holiday on Friday so won't have much real time to deal with it and prepare my talk before then. In the meantime I've "fixed" the problem by replacing a dead 8881 bus driver (E23 on the display board, drives D0-D3 from the switches) with an SN7401. It works with M8300+M8310 CPU, M8330 timing board and M8320 bus loads, but probably doesn't have enough drive capability for a full system. IIRC an 8881 should be capable of sinking 70mA with Vol=0.8V, while a 7401 is only guaranteed for 16mA. I've calculated the terminators alone need 23mA plus around 1.6mA per load (20 loads in a medium system?), and DEC sometimes used selected 7401s marked 97401 presumably for this reason. Anyone got practical experience of substituting for an 8881? -- Pete Peter Turnbull Network Manager Information Directorate, University of York DD: +44 1904 323804