This model seems pretty rare in the UK. I havn't seen one like this on E-Bay but I would have thought $200 was acheivable. I can't remember what I paid for the HP7475A but I think it was around $100. No box but it does have a cover and manual. Dave Wade G4UGM Illegitimi Non Carborundum

On Tue, 19 Jun 2012, Dave McGuire wrote: I picked up two 7550A plotters in the late 1990s from various university auctions for ~$20-25/each. If these plotters are "rare" and now worth $2k as that eBay seller suggests then I think I got a heck of a bargain... ...and they are really, really nice plotters. IIRC, this was the -fastest- plotter HP ever made. They work with Chiplotle http://music.columbia.edu/cmc/chiplotle/ and documentation for these machines can be found at here: http://www.hpmuseum.net/display_item.php?hw=75 http://www.hpmuseum.net/exhibit.php?hwdoc=75 The downside to these plotters is that they require a special serial cable (pinouts can be found online) and replacement carousels and carousel parts are not easy to find.

On 6/20/2012 12:38 PM, Dave wrote: I might make mention that I have one of the 48" plotters with I think an 8 pin tray, and associated accessories if anyone is interested. pick up in Southern California. Jim

On Thu, Jun 21, 2012 at 12:28 AM, Tothwolf <tothwolf at concentric.net> wrote: Plotters are a lot of fun. They're fascinating to watch, they create an output not quite reproducible by other technologies and, with the appropriate job sent to them, they teach patience :) A listmember passed this site to me recently. Not only do they sell pens for a lot of the plotters out there, they have a very handy cross-ref chart to match pens to plotters (and figure out which models are rebadged and might use a pen you already have.) http://www.thetestequipmentstore.com/plotter_pens_charts.htm I've got a Digital LVP16, as well as the equivalent HP model. The LVP uses the same pen as the HP, as do many of the plotters listed there. Those two are multi-pen models. I've also got a couple smaller HP models which are monochrome. And let's not forget the Commodore VIC plotter :) My problem with the multi-pen models is not pens, it's the pen carousels. I've identified the HP part # for them (apologize for not having it handy) but all sources list $sillyprices and are out-of-stock anyway. Anyone have a source for those? j

As am I. I'd actually quite liek a 7550 (there's a 68000 processor in them IIRC), but I am not paying $2000 + shipping for one :-) I even have an HP7470 opt 003 -- the HPIL pone, and the HP41 ROM module to drive it. No it's not up for grabs! The HP9125 plotter is fun too. It conencts to the HP9100 expansion conenctor, it grabes the data from the X and Y regiaters and uses that s the cooridiantes. Inside it's not as complciated as you might think, given it's all discrete transistors. There are 4 boards of logic to interface to the strange 9100 signals (mostly flip-flops and diode gates), 2 DAC boards (3-and-a-bit decades, these things habve over 90 transistos on them), and then essentially an analogue XY plotter conencted to the outputs of the DACs. The do exist in the UK. I haev 2 of them (again, I am keeping them). One is a Houston Instruments, the other a Bryans. Both are (mostly) valved. Making one would be quite a fun project if you have a reasoanble mechancial workshop, actually. The Houston doesn't have any really odd bits. The slidewires are actually multi-turn pots coupled to the drive cables for the 2 axes, which might simplify things. -tony

Does anyone else here have an HP7245? Thia is (I kid you not) a thermal printer/plotter. IT takes special sproketed thermal paper (which is unobtainium nwo, I have a few boxes I use for demonstrations). There's one stepper motor driving a sproketec roller to feed the paper. And anotehr to move the printhead across the paper. The printhead has (IIRC) 13 heater elements on it. 12 are in a diagonal line and are used for printing text (it can print both across and up/down the page, hence the diagonal arangement of the elelemts). In this mode, it prints dot matrix chracters i nthe usual way. teh 13th element is used for plotting. In this mode, the paper and carriage are moved like a pen plotter, the element is turned when the 'pen' should be 'down'. Oh yes, the element temperature is controlled depending on the speed of motion to keep a constant line intensity. It has an HPIB interface and repsonds to 2 consequtive addresses (AFAIK these don't have to only differ in the LSB, they could be addresses 7 an 8, for example). One address is used for printing, you send ASCII text to it and it prints it. THe other is used for plotting, you send HPGL commands there. The control electronics uses an HP 'nanoprocessor' with the normal ROM and RAM. And a lot of TTL for the motor contorl and HPIB interfaces. Oh, and the PSU is one of those that uou hope never to repair, it's a complex switcher spread over about 5 boards. It's certainly a fun device us play with once in a while... I find some of the electromechanical teleprinter terminals (Teleypes, etc) to be fascinating to watch in operation. -tony

For suitable values of 'easily' :-) Actually, it;'s not as simple as that. One sprocket hole every so often on the left edge of the paper is elognated across the paper a bit (prehaps to twice the hromal width). This is detected by the plotter and used as the top-of-form marker. -tony

On 06/20/2012 11:29 PM, dwight elvey wrote: Does that plotter take the pre-7475-style pens with the two little plastic "ears" on the sides, that you insert and turn to lock? I have a 7015B that takes those, and I'm looking for pens. If you think this place would have those, would you please send me their contact information? Thanks, -Dave -- Dave McGuire, AK4HZ New Kensington, PA

Hi Dave It looks like the other guys beat me to it. That is the place I bought my pens from. They seem to have pens for just about anything. Dwight

Hi All Reminded of this, I did a search for Moseley and found an articlethat said that Moseley was bought out by HP. It seems that HPXY plotters got their start with Moseley.The plot thickens ( pun intended ).The search also brought up one of the ebay searches for plotters.There was an early add for a Moseley plotter but also a number ofother XY plotters as well as manuals.Looking to see what was there, I came on a buy it now fora HP 135/135A plotter maintanence manual. I blow up the pictureand what do you think. The knob pannel looked just like my plotter.A closer look even had the Moseley lable on it.I went ahead and bought it of course.I'd been trying to fix the one I had but it looked like the outputtransistors had been failing ( older germanium types ).I'd tried to trace the wiring but it is difficult without cutting thewire ties, that I didn't want to do.With the manual, I'll no longer need to do this.It is interesting, how it works though. Instead of a DC servo motor,it uses an AC synchro motor. It chops the error signal and uses thatto drive the motor. A clever way to avoid DC offset with the earlytransistors.I did get a kick out of one of the ebay adds. The wanted about $200for a plotter and said it was in excellent condition. In the picture,one could clearly see two of the switch toggles broken off. Oops!Dwight

[...] That was not at all uncommon in ploters (and chart recorders) using valve amplifiers (a 'chart recorder' here is a device with one votlage-cotnroled axis (moving the pen across the papar) and one time axis (moving the paper at a constant speed using a synchronos motor and gearbox). WHt was often done in such unts was to take the DC error voltage optained by the differnece between the input nad the slidewire position. THis was then choppend by a vibrating reed device eneerginsed from the heater winding (normlally). The resulting signal conld then be amplifieed in a normal AC-coupled valve amplifier. The amplitude of the output was then the magnitude of the eorror (and thus couple be used to cotnrol the speed of the motor), wehter it was in phase or anitphase iwth the heater winding gave the direction. The output of said amplifier drove one winding of a 2 phase motor, the other widing being mains-supplied (maybe Certainly that Houston Instruments unit I mentioned last night works like this. So do the (well-known over here) Honeywell-Brown 'continuos balance' chart recorders. One minor problem for running thse units now. THe votlage acorss the sliderwire needs to be constant And may need to be flpating wrt to ground. In smome units, this was provided by a mercury cell. Or course those are now unobtainalbe. An alkaline AA cell will do for testing, but don't expect the thing to hold its calibration (if the voltage drops, the thing gets _more_ sensitive). It's not hard to make up a PSU though. -tony

I don't know how early this thing is, but it may have predated the easy/cost-effective aviaalbility of FETs. The point being that a nuvistor has a higher input impedance than a bipolar transistor. Did they contain elemental mercury? Or did you find soem way to extract it from the compounds? If you really want to give the 'greens' a fit, show them a Weston cell. IIRC it's a mercury/cadmium couple. I guess they're banned now too, ala, even thought he environmetal impact is close to xero (they last for a very long time if not misused, and they're sealed glass tubes). Indeed not. But I beelvie there are such compounds in a mercury cell. WHich I beelive is the origian of that phrase, hatters used merucry or mercury compounds for oen of the operations on the felt to make said hats. I prefer 'As mad a as Hacker' :-) (which may well eb caused by breathing flux fumes...) -tony

On 21/06/2012 14:46, dwight elvey wrote: They don't seem to have any for my Hitachi plotter. Looks like these folks have some:- http://www.draftingfurniture.com/listings/Plotterpens.html#2 what I really want are some Staedtler32B23 or 31B23Fiber-tip pens but looks like these are long discontinued. -- Dave Wade G4UGM Illegitimi Non Carborundum

Hi They don't list the 7044A on their chart but the 1CY14xx pens work fine on it as well. I see that they have Dave's plotter list though. Dwight

On Tue, 19 Jun 2012, Dave McGuire wrote: The 7550 will handle 11x17 if you manually place the page. The paper tray only handles 8.5x11 though.

On 19 Jun 2012 at 21:45, dwight elvey wrote: You see that a lot on Craigslist--sellers asking the same above- market price for something that's rapidly declining in value, day after day. Since it costs them nothing to list, I suspect they have an automatic script that runs every day. --Chuck

I thought htere were minor mechancial differneces too, it wasn't a simple rebadging. IIRC when loading paper into the hP one, you have to line the edge up with a mark on the plotter. With the IBM one, there;'s little plastic stop that's raised when you flip the load lever, you just put the paper against that. -tony

On 06/20/2012 06:37 PM, Dave wrote: My 7475A has it. -Dave -- Dave McGuire, AK4HZ New Kensington, PA