Serial UNIBUS Repeater?

Mark J. Blair nf6x at
Mon Jun 15 13:00:42 CDT 2015

> On Jun 15, 2015, at 10:11 , tony duell <ard at> wrote:
>> I'm not specifically familiar with the 11/730, but what's wrong with just cabling up an expansion box "the old 
>> fashioned way" using BC11A cable?
> Nothing electtically... 
> The problem is that the 11/730 mouting box (BA11-Z??) is a bit odd. The boards go in from the left. Cables end up
> going downwards (either straight down or over the top of the card cage, then down between the backplane and
> PSU). Then into a removeable tray on the bottom of the mouting box, round a flexible plastic sheet and to another tray fixed in the rack. The idea is to make the cables route nicely when yout slide the box in and out (something
> you have to do on the 11/730 to change the microcode tape or get to the main circuit breaker).

That's a much better description of the 730's mechanical peculiarities than I came up with. I was more concerned with cable management between the two racks, since I have them in a tiny room where I need to roll them around to get access to the back (it's literally a tiny bedroom in a manufactured home... basically a doublewide trailer that's been fastened to a foundation after having the axles and drawbar cut off!). It's already tricky to roll the racks back into place without running over the power cables, tape drive cables, serial lines and power controller cable. But managing the cables in the cable tray area is another thing that needs to be done right. 

> I am not sure how a BC11A cable would like being folded back and forth like that. The official way was, I think
> a board in the Unibus out slot of the 11/730 that had 3 40 pin Berg headers on it. This took 3 normal 
> 40 way ribbon cables which went round the cable routing thing and to a similar board in the Unibus in slot of the
> expansion box. I think there were even bulkhead panels to route the cables to another rack cabinet.

Three narrower cables sound like they would be easier to manage than one wide one.

Based on the hardware user's guide that I have (and which I do plan to scan and share), I gather that UNIBUS expansion cabinets would generally be used in a configuration that's in a larger rack and has both TU58 slots on the front panel. I haven't seen one of those in person before. My system is the configuration that's in one or two short racks. The main one is completely filled by the RL02, VAX-11/730 and R80 drives, from top to bottom. The other rack contains the optional TU80, with an unused bay below it. I haven't measured the size of that unused bay yet, but it looks like it may be tall enough for a UNIBUS chassis. Maybe I could adapt one of my empty PDP-11/44 chassis boxes for use as an expansion chassis?

Or another possible use for that slot could be for my Kennedy 9610 tape drive. The TU80 looks like it probably has a Pertec interface, so I should be able to add the Kennedy drive to the chain to get more BPI options in the system. Now that I have a computer with a Pertec interface running, buying/building a Pertec adapter for my Mac or Sun doesn't seem so important. Assuming I can bring up networking on the VAX that is, and that I can figure out how to do block-level stuff under VMS.

Mark J. Blair, NF6X <nf6x at>

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