>
>
> Date: Tue, 8 Feb 2022 20:55:31 +0000
> From: Wayne S <Wayne.Sudol at hotmail.com>
> 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
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 <cctech at classiccmp.org> 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
Hi
???????? Jerry Walker and I have an 11/34 under restoration.
We have run into a bit of a problem.
On the M8266 CPU control board a defective 7404 (E111) has killed a
bunch of the PROMs holding the microcode.
Does anybody have or can get images of the PROMs on this board so
replacement devices an be programmed.
Rod
I have many 8mm tapes. A few are new. First comers get new ones.
I have a few 8mm cleaning cassettes
I have about a dozen DLT-II tapes.
I have a Quantum DLT-II drive with wide SCSI LVD/SE interface
I have some Ultrium LTO fibre-channel SCSI drives that were removed
>from a tape-mounting robot several years ago. I never used them in my
computers. The mounting bracket for one was modified to have an
internal power supply -- which might be inadequate. ?I have one LTO
tape.
I have a 5.25" floppy drive.
Yours for the price of shipping, or local pickup OK.
Van Snyder
van.snyder at sbcglobal.net
La Crescenta, CA
> On Feb 8, 2022, at 5:14 PM, Wayne S via cctech <cctech at classiccmp.org> 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
> From: Steve at oldcomputers.net
> There are some vintage tablets in Minneapolis (Eden Prarire) that would
> like, but the seller will not ship.
> Any help?
When dealing with eBaiters who can't/won't ship, I have had good luck with
PakMail (http://www.pakmail.com/); for a usually reasonable fee, they will go
pick something up, package it properly, and ship it.
In my experience with them, the shipping cost may not have been the absolute
lowest possible I could have secured had I been on the spot, looking around,
but.. I wasn't on the spot, looking around. And they went to the person's
house, picked the thing up, and shipped it.
Noel
There are some vintage tablets in Minneapolis (Eden Prarire) that would like, but the seller will not ship.
Any help? You will have to pay, pick up, and ship.
I would do it for you!
Thanks-
Steve in CA
> On Feb 8, 2022, at 2:53 PM, Wayne S via cctech <cctech at classiccmp.org> 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
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 <cctech at classiccmp.org>
> 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 <
>> cctech at 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
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 <
> cctech at 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 <wayne.sudol at hotmail.com> 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 <
>>> cctech at classiccmp.org> wrote:
>>>> ?
>>>>>
>>>>> From: Gary Oliver <go at aerodesic.com>
>>>>> 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
>>
