Log of March 2007 events
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Tuesday, March 20,
Tuesday, March 20
Meeting for Tuesday, March 20 2:00 P/M. in the Von Neumann room.
- Present were Al Hoagland, Dave Bennet, Joe Feng, Dick Oswald, Ed Thelen.
- Dave Bennet presented the track pot that he obtained by swapping - paperwork still being signed -
- Dave says that this pot is electrically and mechanically functional. (Our original pot had a tap connection - which would have been "interesting" to design a controller for.)
Dave said that the mounting bracket casting of the swapped pot was somewhat different, different mounting screw positions and would have held the potentiometer at an awkward distance - so only the pot was swapped, the mounting bracket and gear is from "our" RAMAC.
- Dick Oswald presented:
- These boxes are for logic and switching circuits - the (linear) power supplies to be elsewhere
A 19" rack mount single height box, from WierdStuff, $7.50 ;-))
- Probably three of these boxes will be used
- There was discussion of:
- - cover plate - Dave says there is perforated aluminum at Orchard Supply Hardware
- - probably no fan needed, estimated 25 watt max dissipation per box
- - a mounting rack - a foot or two high, maybe with a cover and door?
- Joe Feng presented two decimal thumb wheel switches - three digits each.
These seemed very suitable to Dick Oswald, who wishes for two more - RAMAC from address, and to address.
- These switches are modular, two end digits and an optional number of inbetween digits.
- Dick Oswald and others then discussed:
- "Snubbing" the turn-off inductive kick from solenoids and clutches. Instead of the usual resistor, he likes to dump the energy into back biased zener diodes (say 150 volt). This drops the current much faster permitting somewhat faster operation. The duty cycle should be sufficiently low to prevent appreciable heating.
- Using a high voltage write current, maybe derived through a regulator from the clutch power supply. We should fuse this carefully to minimize risk to the head.
- Who is making which read/write logic and drivers?
- What is the maximum number of air solenoids energized at a time. Ed Thelen estimated three max - will verify
- What is the rated air solenoid voltage? We thought the students were using 40 volts.
- The air valve name plate says 40 volts, even though IBM used lots of 48 volts.
- We could use the existing plugs and cabling the students purchased/made
- (maybe twisting/shielding the long read sense wires?)
- Would 1401 restoration people be interested in helping?
- There is a 1405 RAMAC in Australia/New Zealang? - who said? where? schematics?
- Dick Oswald said he has a stack of (which?) schematics at his house.
- Should we help pay the tab that various members are running up?
- When can Dick use some "volunteer" help constructing his circuits?