Somebody said something recently about wanting an RRD-42 or two. I just
found two of them in my pile of obselete electronics and I don't need them.
I also found two RRD-40s but my VAX3000/30 is fond of those. I did not
find any RRD-45s which my AS4100 has a taste for.
Speak up if you are looking for an RRD-42, I can also throw in the spiffy
little CD carrier.
--
Richard Loken VE6BSV, Unix System Administrator : "Anybody can be a father
Athabasca University : but you have to earn
Athabasca, Alberta Canada : the title of 'daddy'"
** richardlo at admin.athabascau.ca ** : - Lynn Johnston
> From: Dave G4UGM
> I found it easier to think of it in DC terms. So the Cap charges
> through R5 + R3 and R9 + R8.
> As the Cap charges the voltage on the base of Q1 rises until it turns
> on, which then turns on Q2.
> At this point the cap is then charged (or discharged) in the reverse
> direction via Q2, D5 and R4 until Q1 turns off.....
I'm clearly never going to be any good at analog stuff! ;-) Even with what
looks (on the surface) to be a wonderfully clear explanation of how the
circuit works, I still can't really grok how it operates!
I mean, I can tell from the polarity on the cap that the collector of Q2 must
be at a higher voltage than the base of Q1, but I am utterly failing to
understand how the cap discharges through Q2. And as the cap charges (i.e.
the voltage across it increases), how does the voltage on the base of Q1
increase - surely it must be decreasing (since it's tied to the negative side
of the cap, which is experiencing a voltage increase across itself)?
Like I said, I apparently don't have the gene for analog... :-)
Noel
> From: Pontus Pihlgren
> One computer I could imagine would sparc interest is a new PDP-6.
Umm, perhaps not the best choice! The original PDP-6 was known for being, ah,
flaky. There's a reason DEC sold less of them than any other DEC machine!
(Nothing wrong with the _architecture_, mind - the KA-10, which is basically
identical, was _very_ successful. It was purely the implementation.)
Noel
>
> Date: Mon, 15 Jun 2015 19:42:42 -0400
> From: Michael Thompson <michael.99.thompson at gmail.com>
> To: cctech <cctech at classiccmp.org>
>
> The M452 creates a 220 Hz clock for the TTY transmitter and a 880 Hz clock
> for the TTY receiver.
> The M405 for the DP12-B serial port generated a clock that is 16x the baud
> rate which is then divided by an M216 module.
>
> Michael Thompson
>
>
Just to prolong this discussion...
The PDP-12 came to us with an M452 for the 110 baud TTY console and a
home-made adjustable baud rate module for the second serial port. The
adjustable baud rate generator was made by the original user of the system
in the early 80s, and is just a crystal, rotary switch and a Fairchild
4702. I ordered a replacement Intersil IM4702 so we can repair the module.
The original owner doesn't remember ever having an M405 for the second
serial port.
--
Michael Thompson
I am humbled (yes, it is possible!) .... got a very nice email from
Homebrew Computer Club moderator / SOL-20 co-developer / Osborne 1 chief
engineer (and many more):
"This book presents the history of personal, portable computing from the
abacus to the present day in a remarkably thorough, accessible fashion.
Not only the winners are described but the also-rans and
almost-made-its. Koblentz has done an admirable job of research and
description in covering the field.
I've always been careful to claim that my Osborne-1 design was only the
"first commercially-successful portable computer" because I knew that a
book like this would be forthcoming to show the time lines, descriptions
and designers of earlier efforts. By nature a survey of the field, it is
thoroughly researched and can provide pointers to more in-depth
investigations."
Evan again: still just eight bucks in PDF edition.
http://www.abacustosmartphone.com.
Also: This is version "1.0"; all first-batch readers will also get the
PDF of version 1.x for free when it's ready.
As long as we're talking philosophy, what do y'all think about emulating the TU58 drive, vs. emulating the TU58 *tape*?
I cannot properly express my opinion of that tape cartridge design even if I violate list rules about use of profanity. But the drive itself isn't all that bad, aside from not having enough motors to manipulate a well-designed tape cartridge mechanism.
Emulating the whole tape drive is pretty easy since it helpfully interfaces over a plain old asynchronous serial port. But replacing the whole drive with an emulator, or worse yet tethering its computer to a modern computer, leaves a bit of an empty feeling if one likes their vintage machines to be original. There's something missing when you don't hear the drive whirring, and the system boot completes within a modern attention span.
But what about emulating the tape cartridge, instead? Imagine a gizmo in the form factor of a TU58 cartridge, containing a wheel for the capstan roller to engage, but connected to an encoder instead of the ******* ************ ***** ** **** belt drive of an original cartridge? Where the tape would normally be exposed, there is instead a magnetic head which rests against the tape drive head like in one of those gizmos for injecting line level audio into an audio cassette drive. It might need an external power source, but for the sake of argument, let's pretend that a suitable rechargeable battery can be embedded. Maybe it has an SD card slot on the rear, or maybe it looks just like a real TU58 cartridge when inserted, and you swap the whole thing to change tapes (this is open for discussion).
Would this be more or less acceptable in terms of keeping the system as close to original as possible, vs. unplugging the original drive and plugging in a drive emulator?
No, I'm not going to build the thing. I'll just build my TU58 drive emulator to fit in the cartridge slot but plug into the computer in place of the original drive, with the cables snaked through the original drive mechanism. And I'll feel a little bit dirty, but the thing will work reliably and will be easy to implement. I'm just curious about the philosophical implications of my silly cartridge emulator idea.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
> From: wulfman
> 2.47 per each ic is kinda expensive
US$170 / 420 ICs = US$.40 per IC? (I suspect you swapped the numerator and
demoninator: 420 / 170 = 2.47.)
Seems not too unreasonable. I did order one, we'll see what it looks like
(thanks to the OP for the tip).
> i have 10s of thousands of each 74 series part there was ever made been
> collecting on ebay for 15 years
Want to get rid of some of the excess? :-)
Noel
> From: tony duell
> One method that works for me is that if you are buying a fairly cheap
> part, buy 10 of them and put the rest in stock. Or more than 10 if it
> is something really common.
I suspect a lot of us do that - that's why I have tubes of 4164's, etc, for
instance. It makes a lot of sense, because it's trivial to implement - it's
just as much work to order 10 of something, as 1.
But that model isn't really the best, because a lot of the time one winds up
needing something one doesn't already have. Which is why it's better to lay
in a diversified stock up front. E.g. in wood screws (I do a lot of work in
wood, mostly furniture), I have a fairly comprehensive collection; from #6
through #12, all the available lengths (not the very longest ones, though),
counter-sunk and round-headed, with both slot and Phillips drive.
But doing so in IC's - oi vey! Just in TTL alone, there are dozens of common
parts (hundreds, if you count the more obscure ones), and then you get into
the whole 74, 74S, 74LS, 74ALS, 74L, 74H, 74F, yadda-yadda. Of course, most
of the variants one would never need, but one can't get by with just, e.g.
LS; e.g. if I ever get my wish and wind up with a PDP-11/45, that's mostly S,
IIRC.
I wish there was some _easy_ way to lay in a stock of the most common TTL
IC's - e.g. some kind of kit one could buy - but alas, I don't know of any.
(Hence my dream of finding and acquiring someone else's collection! :-)
Suggestions for the source of such a good diversified 'starter kit' welcome...
Noel
Has anybody ever made a UNIBUS repeater with a high speed serial link between the bus segments yet? I'm curious because my VAX-11/730 backplane is full, and it would be nice to be able to experiment with additional hardware without needing to pull out one of the existing boards, i.e., adding a TK50 interface without removing the DEUNA, adding a SCSI card to boot from a scsi2sd without pulling the integrated drive controller, etc. There's a blank spot in the TU80 cabinet that looks like it may be tall enough for an expansion chassis, but the thought of adding more big ribbon cables to the belly plate area and then routing them between racks doesn't appeal to me. Running something like a CAT5 cable between the two racks would be a lot easier. Another application would be for placing a small remote UNIBUS backplane on the test bench for easy access, and cabling it to a VAX or PDP-11 elsewhere in the room.
This should be quite possible with modern hardware, but I'm curious about whether something similar has been done before.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
