DEC 874-A Power Conditioner

BTW, what I did manage to get done in the past few weeks, is an "upgrade" of two 861's. I replaced the big electromagnetic relay with a modern Solid State Relay. If you install an SSR with zero-crossing detection switch-on, instead of the old relay, the power surge of the big transformer in the bigger UNIBUS PDP-11's will not trip the fuse in the house. It is fairly simple, and if you keep the old relay, you can alwyas revert to the original situation. Here's what I did. 0. Get a SSR with input 3-32VDC. The output is AC rating what you have at home (for your PDP-11's). 1. Get the diagrams from bitsavers. Not really necessary, but they will make you understand better how an 861 works. 2. Remove the electromagnetic relay. 3. Install the SSR (I had to drill one hole, sorry ...) 4. Remove the pilot control board. 5. Cut the trace that connects the reed relay to the *AC* power. The other trace goes to the relay. It depends a little on the type of board, as I have seen a few small differences. 6. Connect the cut trace (to the reed contact) to the "+" of the electrolytic cap. 7. Connect the "-" wire from the electrolytic cap to the "-" of the SSR input. And connect the other contact of the reed relay to the "+" of the SSR relay. 8. Lead one wire from the AC breaker directly to the output cap. From the output cap straight to the AC power socket (Neutral). 9. Lead the "hot" wire from the AC breaker to the SSR AC LOAD input, and a wire from the SSR AC LOAD output to the other contact of the AC power socket (Phase, "hot"). Before you apply power (stand-alnoe, just the 861 box!) check the wiring at least once ...! I haven't had a tripping fuse up till now when I turn on the 11/34. - Henk, PA8PDP. ________________________________ Van: cctalk-bounces at classiccmp.org namens Richard Verzonden: wo 04-01-2006 18:56 Aan: General Discussion: On-Topic and Off-Topic Posts Onderwerp: Re: DEC 874-A Power Conditioner In article <10601040813.ZM28391 at mindy.dunnington.plus.com>, Pete Turnbull <pete at dunnington.plus.com> writes: Mine is labelled "AUX On/Off" and I didn't know what it did. On the 861 power conditioner there is a connector labelled J2. Is this where the switch connects up? -- "The Direct3D Graphics Pipeline"-- code samples, sample chapter, FAQ: <http://www.xmission.com/~legalize/book/ <http://www.xmission.com/~legalize/book/> > Pilgrimage: Utah's annual demoparty <http://pilgrimage.scene.org <http://pilgrimage.scene.org> > This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message. Thank you for your cooperation.