Re: DECTape head problem (I've uploaded pictures)
Some folks asked for pictures and information about my Astrotype DECtape project. I've uploaded some pictures and other details to the web for your enjoyment. http://xx2247.com contains some photos and first-draft information about the components. I'll update this site from time-to-time as I make progress. -Gary
Re: DECTape head problem
On 2/9/22 10:54, Michael Thompson via cctech wrote: Date: Tue, 8 Feb 2022 20:55:31 + From: Wayne S Subject: Re: DECTape head problem So it serms dectape heads are special. I don?t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? We have one from Applied Magnetics Corporation, maybe the one in Goleta, CA. I can't find them. Lots of lost info (even Bloomberg has info, but the web site listed goes to a parking 'for sale' page.) Documents suggest they "merged out" in 1987 (but no pointers to who gobbled them up.) I have sent a request for information from jrfmagnetics.com (thanks Tom!) and will see what they say. It's seems they are still 'lingering' in the head repair business, so it's remotely possible they could do a repair job. Thanks all. If anyone has a working head they aren't using, I'd entertain an offer... :-) -Gary
Re: DECTape head problem
> > > Date: Tue, 8 Feb 2022 20:55:31 + > From: Wayne S > Subject: Re: DECTape head problem > > So it serms dectape heads are special. I don?t think Dec would have the > desire to make them internally so they probably contractef with a company > already set up to do that. Who were the big tape head manufacturers at that > time? Does anyone know? > We have one from Applied Magnetics Corporation, maybe the one in Goleta, CA. -- Michael Thompson
Re: DECTape head problem
On 2/8/22 15:49, Paul Koning via cctalk wrote: The maintenance manual (on Bitsavers) speaks of a "read/write head" and has an illustration that shows one of the head elements with a "read/write coil". So the implication is that (a) there isn't an erase head, and (b) the same head serves for read or write according to whether the coil is being driven or sensed. Yes, that is right. Come to think of it, I think erase heads are an aspect of audio tapes, not relevant to computer tapes. No, all 9-track drives that I know of have erase heads that erase the tape to a no-transitions state before it is written on. This allows you to obliterate old data when writing a new record, and leave gaps between records. Since DecTape was synchronized by clock and mark tracks, that was not needed. Jon
Re: DECTape head problem
You could try: http://www.jrfmagnetics.com/ Tom On Wed, Feb 9, 2022 at 3:06 PM Gary Oliver via cctalk wrote: > On 2/8/22 14:14, Wayne S via cctech wrote: > > Searched a lille bit for Western Magnetics. Here’s a site that has some > surplus heads, even a western magnetics onebut probably not the correct > one. There is a corporate charter record for Western Magnetics in Minnesota > dated 1964. Maybe this is the same company. There’s also a tape head from > Michigan Magnetics. Maybe a merged company? > > > > https://www.surplussales.com/Equipment/magnetic-tape.html > > > > > > Sent from my iPhone > > > > On Feb 8, 2022, at 13:05, Ron Pool via cctech > wrote: > > > > > > So it sermsdectape heads are special. I don’t think Dec would have the > desire to make them internally so they probably contractef with a company > already set up to do that. Who were the big tape head manufacturers at that > time? Does anyone know? > > > > A photo of the back of a TU56 DECtape head can be seen at > https://www.pdp8online.com/tu56/pics/head_label.shtml?small . > > The head has a label on it that reads: > > Western Magnetics > > Glendale Calif. > > Record > > 7282 > > > > I've never seen a TU56 in person and have no idea if they have separate > read, write, and erase heads or some other combo. The "Record" notation on > the above head's label hints to me this might be a write head. > > > > I found that and other DECtape photos at > https://www.pdp8online.com/tu56/tu56.shtml . > > > > -- Ron > > > > > Thanks. Hadn't seen the Minnesota information. Found some references > but not actual company info. Did find a reference somewhere it Canada, > but I couldn't tell if it was original or successor company. At any > rate, no web presence nor telephone numbers found (yet.) > > I've dealt with the SurplusSales (of Nebraska) many times. His prices > are usually pretty high (not obscene, but just not 'surplus' prices I'm > used to.) However, he is a first-rate dealer and when he says something > is so, you can count on it. Never had problem with anything I was > willing to *PAY* for. I scanned the list you provided and found only a > few 'digital' devices, unfortunately. I suspect from 7 and 9 track mag > tape drives. I will scan his site and send him a ping so he'll be on > the lookout. > > -Gary > > >
Re: DECTape head problem
On 2/8/22 14:14, Wayne S via cctech wrote: Searched a lille bit for Western Magnetics. Here’s a site that has some surplus heads, even a western magnetics onebut probably not the correct one. There is a corporate charter record for Western Magnetics in Minnesota dated 1964. Maybe this is the same company. There’s also a tape head from Michigan Magnetics. Maybe a merged company? https://www.surplussales.com/Equipment/magnetic-tape.html Sent from my iPhone On Feb 8, 2022, at 13:05, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Thanks. Hadn't seen the Minnesota information. Found some references but not actual company info. Did find a reference somewhere it Canada, but I couldn't tell if it was original or successor company. At any rate, no web presence nor telephone numbers found (yet.) I've dealt with the SurplusSales (of Nebraska) many times. His prices are usually pretty high (not obscene, but just not 'surplus' prices I'm used to.) However, he is a first-rate dealer and when he says something is so, you can count on it. Never had problem with anything I was willing to *PAY* for. I scanned the list you provided and found only a few 'digital' devices, unfortunately. I suspect from 7 and 9 track mag tape drives. I will scan his site and send him a ping so he'll be on the lookout. -Gary
Re: DECTape head problem
> On Feb 8, 2022, at 5:14 PM, Wayne S via cctech wrote: > > Searched a lille bit for Western Magnetics. Here’s a site that has some > surplus heads, even a western magnetics onebut probably not the correct one. > There is a corporate charter record for Western Magnetics in Minnesota dated > 1964. Maybe this is the same company. There’s also a tape head from Michigan > Magnetics. Maybe a merged company? > > https://www.surplussales.com/Equipment/magnetic-tape.html Those all look like audio heads, nothing even vaguely resembling a DECtape head. paul
Re: DECTape head problem
> On Feb 8, 2022, at 4:04 PM, Ron Pool via cctech wrote: > >> So it sermsdectape heads are special. I don’t think Dec would have the >> desire to make them internally so they probably contractef with a company >> already set up to do that. Who were the big tape head manufacturers at that >> time? Does anyone know? > > A photo of the back of a TU56 DECtape head can be seen at > https://www.pdp8online.com/tu56/pics/head_label.shtml?small . > The head has a label on it that reads: > Western Magnetics > Glendale Calif. > Record > 7282 > > I've never seen a TU56 in person and have no idea if they have separate read, > write, and erase heads or some other combo. The "Record" notation on the > above head's label hints to me this might be a write head. > > I found that and other DECtape photos at > https://www.pdp8online.com/tu56/tu56.shtml . This picture https://www.pdp8online.com/tu56/pics/TU56_front.shtml?large shows the tape path clearly. There is just one head assembly that performs reading as well as writing. I don't know what "Record" refers to; the numbers near it look vaguely like a date code though not the usual year and week number. The maintenance manual (on Bitsavers) speaks of a "read/write head" and has an illustration that shows one of the head elements with a "read/write coil". So the implication is that (a) there isn't an erase head, and (b) the same head serves for read or write according to whether the coil is being driven or sensed. Come to think of it, I think erase heads are an aspect of audio tapes, not relevant to computer tapes. paul
Re: DECTape head problem
On 2/8/22 13:04, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Mine also says Western Magnetics, Glendale CA, but does not have a part number. Just serial numbers. At least I assume they are serial numbers "19984" and "19976". I've seen evidence that a few souls in the 50s managed to make magnetic heads from scratch (heck, Ivan Sutherland is claimed to have made a functioning magnet drum storage device when he was in 12th grade,) so give the modern world of CNC milling and availability of every manner of sheet metal via Internet searchers, I figured their just *might* be a possibility of growing one of these from scratch - tolerances (other than head gap) appear pretty generous, but I just don't have enough info to crack what the coil construction is to be. There may be enough information to do a stab at it, but I'm not sure I have the energy (or even the skill) to give it a credible effort. I've seen evidence of 'head repair' services, but I doubt they include digging out the wires from solid epoxy. Any information available would be appreciated. -Gary
Re: DECTape head problem
On 2/8/22 13:04, Ron Pool via cctech wrote: So it sermsdectape heads are special. I don’t think Dec would have the desire to make them internally so they probably contractef with a company already set up to do that. Who were the big tape head manufacturers at that time? Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron Mine also says Western Magnetics, Glendale CA, but does not have a part number. Just serial numbers. At least I assume they are serial numbers "19984" and "19976". I've seen evidence that a few souls in the 50s managed to make magnetic heads from scratch (heck, Ivan Sutherland is claimed to have made a functioning magnet drum storage device when he was in 12th grade,) so give the modern world of CNC milling and availability of every manner of sheet metal via Internet searchers, I figured their just *might* be a possibility of growing one of these from scratch - tolerances (other than head gap) appear pretty generous, but I just don't have enough info to crack what the coil construction is to be. There may be enough information to do a stab at it, but I'm not sure I have the energy (or even the skill) to give it a credible effort. I've seen evidence of 'head repair' services, but I doubt they include digging out the wires from solid epoxy. Any information available would be appreciated. -Gary -- -Gary
RE: DECTape head problem
> So it sermsdectape heads are special. I don’t think Dec would have the desire > to make them internally so they probably contractef with a company already > set up to do that. Who were the big tape head manufacturers at that time? > Does anyone know? A photo of the back of a TU56 DECtape head can be seen at https://www.pdp8online.com/tu56/pics/head_label.shtml?small . The head has a label on it that reads: Western Magnetics Glendale Calif. Record 7282 I've never seen a TU56 in person and have no idea if they have separate read, write, and erase heads or some other combo. The "Record" notation on the above head's label hints to me this might be a write head. I found that and other DECtape photos at https://www.pdp8online.com/tu56/tu56.shtml . -- Ron
Re: DECTape head problem
> On Feb 8, 2022, at 2:53 PM, Wayne S via cctech wrote: > > Since so many audio tape players and computer magtape units were made it > would stand to reason that there has to be a stash somewhere of tape heads > and it’s just a matter of finding where they are. > Are there any part numbers on the dectape heads? The schematics are bound to show DEC part numbers, but how those translate into supplier part numbers is anyone's guess. Or perhaps they were made internaly by DEC? In any case, DECtape heads are unusual. Computer tapes are normally 1/2 inch wide (a few old tape drives had different widths, like the 14 track 1 inch CDC tape). But DECtape and LINCtape are 3/4 inches wide, with 10 head positions. Audio tapes are unlikely to be helpful; consumer reel to reel tape is 2 tracks (interleaved for when you flip over the reel?) 1/4 inch; professional decks might have 8 tracks or more on 1/2 or 1 or 2 inch wide tape, but I don't remember ever seeing 3/4 inch wide audio or instrumentation heads. paul
Re: DECTape head problem
On 2/7/22 12:48, Marc Howard via cctech wrote: The problem would be the non-standard track size and number of tracks. However if at least one of the head's paired tracks is good you could potentially cut the drive current in half and double the read amplitude and just use one track for the affected channel. Marc On Mon, Feb 7, 2022 at 12:33 PM Wayne S via cctech wrote: I’ve often wondered if the tape heads from consumer tape devices such as cassette or 4-8 track tape players could be used or be made to be used as replacements. Anybody ever try that? Sent from my iPhone On Feb 7, 2022, at 11:51, Michael Thompson via cctech < cct...@classiccmp.org> wrote: Further, the DECTape had various track-to-track spacing. Between the the Mark track and the first data track on both edges, the spacing is at a little less than twice that between the mark and timing tracks or between each set of data tracks. Put a different way, the track spacing is: T.M..D.D.D.D.D.D..M.T The magnetic poles of each head is roughly 1mm wide with about .8 mm spacing heads The '..' in the above means there is about 1.4mm spacing (between 'M and D' and 'D and M', for example - the measurements are crude, so I could be off 20% or more.) I've searched the documents I have (many from bitsavers) and haven't yet spied a specification for the head design. I suppose if I could determine the head 'gap' and knowing the magnetic flux required of the tape (with proper margins) and knowing the stated impedance of the head and drive current, I could figure out how many turns of some size wire is required (looks to be at least as small as #40). Back when I was a bit younger and less experienced (and didn't know it was impossible,) I actually 'repaired' (for some definition of 'repair') an old 1/4 inch tape head. But all I did was pull some wire off the coil and delicately soldered a tap to this wire. It worked ok for a couple of years but was obviously failed again from rough handling. Fortunately it was 'easy' since there wasn't a bunch of clear epoxy in the way ;-) I'm not sure today I would have the temerity to even try. Hoping one will show up someday and I can make a deal as to complete my unit. Thanks to all who have replied. -Gary
Re: DECTape head problem
I wonder if there are any professional audio multi-track recorders that match the tape width, number of tracks and tack pitch and have the necessary frequency response. On 2/7/2022 3:05 PM, Marc Howard via cctech wrote: 8 track tapes use 1/4" wide tape. Most 8 track units use heads with only two tracks implemented. There was a stepper solenoid that moved the head down (or up after all 4 stereo programs were played). Growing up in the 60s you never forget things like listening to In-A-Gadda-Da_Vida fade in the middle of the drum solo and a loud "klunk-klunk" sound and the song resuming. Some true 8 track heads were made for mastering pre-recorded tapes and maybe for consumer recorders. Marc On Mon, Feb 7, 2022 at 12:51 PM Michael Thompson via cctech < cct...@classiccmp.org> wrote: DECtapes have 5x redundant tracks. If you could find an 8-track head that had the same track pitch, and maybe track width, you could read the tape but lose redundancy on the Mark and Timing tracks. That probably would not work with a marginal DECtape. On Mon, Feb 7, 2022 at 3:33 PM Wayne S wrote: I’ve often wondered if the tape heads from consumer tape devices such as cassette or 4-8 track tape players could be used or be made to be used as replacements. Anybody ever try that? Sent from my iPhone On Feb 7, 2022, at 11:51, Michael Thompson via cctech < cct...@classiccmp.org> wrote: From: Gary Oliver Subject: DECTape head problem In debugging my DECtape interface lashup, I found that one of my head has two open windings.? Specifically, one channel has an open 'ground' with the other two lines apparently the full winding of the channel.? The second channel failing has no continuity between any of the three lines.? I have tested the other head and it has all the requisite continuity so I'm hoping I can at least get a single spindle running. Has any ever attempted repair of one of these? -Gary At the Rhode Island Computer Museum we found several DECtape heads on TU55 and TU56 drives with open connections. A volunteer got one head X-Rayed so we could see the solder joints between the tiny wires for the head coils, and the larger twinax wires that go to the relay board. We couldn't see any damage to the wires or solder joints. We tried heating the potting material to soften it, and digging it out to get to the solder joints. While digging at the potting material you can't see the tiny wires, so they will likely get damaged. We considered using a solvent to remove the potting material, but thought that it would eat the enamel off the head coil wires and damage them beyond repair. So far we haven't found a way to repair the heads. Michael Thompson -- Michael Thompson
Re: DECTape head problem
DECtapes have 5x redundant tracks. If you could find an 8-track head that had the same track pitch, and maybe track width, you could read the tape but lose redundancy on the Mark and Timing tracks. That probably would not work with a marginal DECtape. On Mon, Feb 7, 2022 at 3:33 PM Wayne S wrote: > I’ve often wondered if the tape heads from consumer tape devices such as > cassette or 4-8 track tape players could be used or be made to be used as > replacements. Anybody ever try that? > > Sent from my iPhone > > > On Feb 7, 2022, at 11:51, Michael Thompson via cctech < > cct...@classiccmp.org> wrote: > > > > > >> > >> > >> From: Gary Oliver > >> Subject: DECTape head problem > >> > >> In debugging my DECtape interface lashup, I found that one of my head > >> has two open windings.? Specifically, one channel has an open 'ground' > >> with the other two lines apparently the full winding of the channel.? > >> The second channel failing has no continuity between any of the three > >> lines.? I have tested the other head and it has all the requisite > >> continuity so I'm hoping I can at least get a single spindle running. > >> > >> Has any ever attempted repair of one of these? > >> > >> -Gary > >> > > > > At the Rhode Island Computer Museum we found several DECtape heads on > TU55 > > and TU56 drives with open connections. A volunteer got one head X-Rayed > so > > we could see the solder joints between the tiny wires for the head coils, > > and the larger twinax wires that go to the relay board. We couldn't see > any > > damage to the wires or solder joints. > > > > We tried heating the potting material to soften it, and digging it out to > > get to the solder joints. While digging at the potting material you can't > > see the tiny wires, so they will likely get damaged. > > > > We considered using a solvent to remove the potting material, but thought > > that it would eat the enamel off the head coil wires and damage them > beyond > > repair. > > > > So far we haven't found a way to repair the heads. > > > > Michael Thompson > -- Michael Thompson
Re: DECTape head problem
> > From: Gary Oliver > Subject: DECTape head problem > > In debugging my DECtape interface lashup, I found that one of my head > has two open windings.? Specifically, one channel has an open 'ground' > with the other two lines apparently the full winding of the channel.? > The second channel failing has no continuity between any of the three > lines.? I have tested the other head and it has all the requisite > continuity so I'm hoping I can at least get a single spindle running. > > Has any ever attempted repair of one of these? > > -Gary > At the Rhode Island Computer Museum we found several DECtape heads on TU55 and TU56 drives with open connections. A volunteer got one head X-Rayed so we could see the solder joints between the tiny wires for the head coils, and the larger twinax wires that go to the relay board. We couldn't see any damage to the wires or solder joints. We tried heating the potting material to soften it, and digging it out to get to the solder joints. While digging at the potting material you can't see the tiny wires, so they will likely get damaged. We considered using a solvent to remove the potting material, but thought that it would eat the enamel off the head coil wires and damage them beyond repair. So far we haven't found a way to repair the heads. Michael Thompson
