Weird TS05 gotcha

I just wanted to share an interesting experience that might save someone else some time if the occasion should arise... I've got a Q4 cabinet with two BA23s in the middle, an RA81 below them and a TS05 tape station on top. It's had a KA630 (a MicroVAX II, that is) CPU running VAX/VMS, Ultrix and 4.3BSD-Reno before, and the TS05 has always behaved perfectly. Just recently, I reconfigured this box with a MicroPDP-11/73 (a great little system: two RD54s, twin RX50s, TK50 and TS05, DELQA, DHQ11 and the RA81), and was dismayed to find that my trusty old 9 track tape station no longer worked! After several, unsuccessful attempts to get some (too) old diagnostic software to work, I put the KA630 back in, and ran MDM, the MicroVAX Diagnostic Monitor. The tape station checked out perfectly. Back in went the 11/73 -- sure enough, it didn't work. Experimenting showed that I could fsf, bsf rewind and stat the tape station with mt all I wanted, but I couldn't read nor write. The controller always gave an illegal address error, which the manual says is what happens when you use it in a 22 bit qbus while it's configured for 18 bit operation. Of course, that couldn't be for real, right? I mean, the KA630 is a 22 bit system, and it worked on that with several operating systems! Still, it doesn't hurt to check, so I pulled the controller. Yup, it was set to 18 bit mode. Flipped it to 22, turned on buffering at the same time -- and I now have a fast, dependable 1600bpi 9 track again! If anyone can explain how this thing worked in the first place, I'd appreciate it! (Oh, and if anyone has some hints for this youngster about the proper care and feeding of my TS05 as the years go by, that would come in very handy as well!) (Heck, while I'm asking all this, an RK05 with qbus controller and a few packs would be great, too, and would go real well with this old /23 I've got sitting here!) -tih -- Popularity is the hallmark of mediocrity. --Niles Crane, "Frasier"