15 Jun
2015
15 Jun
'15
5:19 p.m.
From: Mark J. Blair
I could replace an M1 Carbine trigger spring on the
spot, or a HMMWV
taillamp housing ... Should I criticize you for not having SAE grade 8
hardware on hand, or Bristo wrenches
I think Tony's point was that someone who's into vintage computers ought to
have a stock of suitable parts for them.
So unless he's into older guns, or cars, were he not to have things like SAE
8 hardware around, that would be understandable - he doesn't do them.
Having said that, _I_ don't have 2N3904s nor NE555s around either! I do have
a modest number of parts (e.g. 4164's, 40-ping Berg shells, .250 tab
hardware, etc, etc) - a large enough collection that I just had to
re-organize and add more parts holders (although that was mostly because I
went berserk at the local Radio Shack in the 80% off sale). But it takes a
long time to build up a really comprehensive collection of parts.
It's funny, I was thinking of this exact topic last night - wondering if I
could find someone who's selling off a large cabinet full of mixed spares! (I
was thinking of the experience of one list member, who lucked into such.) I
could certainly use it!
Noel
15 Jun
15 Jun
5:44 p.m.
On Jun 15, 2015, at 2:19 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
Having said that, _I_ don't have 2N3904s nor
NE555s around either! I do have
a modest number of parts (e.g. 4164's, 40-ping Berg shells, .250 tab
hardware, etc, etc) - a large enough collection that I just had to
re-organize and add more parts holders (although that was mostly because I
went berserk at the local Radio Shack in the 80% off sale). But it takes a
long time to build up a really comprehensive collection of parts.
I got into the arcade & pinball hobby over a decade ago, would travel to people home?s
and fix their machines, and really got into the retro computing thing about 3 years ago. I
don?t have a huge collection of parts either, just what I bought to fix something or make
something. One nice thing is there is a lot of crossover of technology with both hobbies,
so I?m often surprised to find I happen to already have something on hand.
What sucks is ordering things that I actually *did* have because I didn?t know. I?ve
slowly started to be a little more organized but things are still scattered all over in
different boxes. I decided to standardize on those 24 compartment and 18 compartment
storage containers from Harbor Freight since they fit quite well in the wooden crates I?ve
been making.
http://imgur.com/a/UsFn3
--
Follow me on twitter: @FozzTexx
Check out my blog: http://insentricity.com
6:11 p.m.
On Jun 15, 2015, at 14:19 , Noel Chiappa <jnc at
mercury.lcs.mit.edu> wrote:
I think Tony's point was that someone who's into vintage computers ought to
have a stock of suitable parts for them.
Yes, that'll likely be true once they have been in the hobby for a while. But for
somebody who has gotten into it recently, and otherwise hasn't had reason to touch a
DIP packaged part since the early 1990s (even while being a full-time electrical engineer
and full-time electronics/etc. hobbyist), it can't be taken for granted that they have
a parts drawer full of misc. 74LS parts. I have a vast junkbox, and I regularly order
electronic components both professionally and for my hobby... and I still don't have a
lot of TTL parts on hand.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
6:37 p.m.
I suppose it depends on what you're working on ... I have a BSEE but only
practice as a hobby ... and I am still mostly in the DIP, through-hole era
... by choice, I suppose ... I wanted to move beyond the level of depending
on pre-manufactured development or demonstrator boards and understand how
to rough-in all the support components from a clean slate ... I use
solderless breadboards for convenience and DIP parts work best there ...
Most things in retrocomputing ... and in building little
single-board-computers and small scale embedded projects typical of most
electronics hobbyists ... can be done still using through-hole/DIP and I
think it will remain with us for a while yet.
Now, yes, I am working in CMOS if I can; or LSTTL if circumstances require
i.e. building a SBC with TTL CPU and support chips ... it's true ...
finding the original 7400 or 74S or 74F is getting a bit challenging & more
expensive but they're still out there ... Jameco's got a decent stock, yet.
Sure, the pre-manufactured boards can allow you to prototype quickly... but
I think Tony is kind of bemoaning the loss of the "old way" and I respect
that ... I kind of miss it myself, even though I wasn't there to experience
it first-hand ...
How are everyone's parts bins so empty? My dad is a practicing EE of over
40 years and he tends to take a pretty dim view of hobby work ... he's all
business .. but even he's got boxes full of random old components and parts
that made their way home from the office scrap and were accumulated over
the course of his career ... as he goes thru and tosses them out, I'm happy
to ensure they get a good home long-term :O
Best,
Sean
On Mon, Jun 15, 2015 at 6:11 PM, Mark J. Blair <nf6x at nf6x.net> wrote:
On Jun 15, 2015, at 14:19 , Noel Chiappa <jnc
at mercury.lcs.mit.edu>
wrote:
I think Tony's point was that someone
who's into vintage computers ought
to
have a stock of suitable parts for them.
Yes, that'll likely be true once they have been in the hobby for a while.
But for somebody who has gotten into it recently, and otherwise hasn't had
reason to touch a DIP packaged part since the early 1990s (even while being
a full-time electrical engineer and full-time electronics/etc. hobbyist),
it can't be taken for granted that they have a parts drawer full of misc.
74LS parts. I have a vast junkbox, and I regularly order electronic
components both professionally and for my hobby... and I still don't have a
lot of TTL parts on hand.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
16 Jun
16 Jun
9:54 a.m.
Sure, the pre-manufactured boards can allow you to
prototype quickly... but
I think Tony is kind of bemoaning the loss of the "old way" and I respect
that ... I kind of miss it myself, even though I wasn't there to experience
it first-hand ...
It's also that this is the 'classic computers' list. To me, classic computing
means rather
more than just the hardware. It also covers the design and construction methods,
technology
and so on. And there seems to be precious little of that in a modern microcontroller
acting
as a clock oscillator.
I find it odd that people want to have a lights-and-switches panel, but are prepared to
totally
adulterate the hardware of the machine that drives it.
As an aside, when I restore m 11/730 I am in 2 minds as to what to do about the microcode
load
device. a TU58 emulator is certainly convenient, but I actually would rather get the real
tape drives
working if at all possible. After all that is what the machine was designed to use.
How are everyone's parts bins so empty? My dad is
a practicing EE of over
Mine isn't, but then you knew that, right :-). When I moved house recently I think I
had
over 30 packing boxes of modern-ish components and more of valves and CRTs. Not
counting the dozen or so boxes of PCBs (some to use, some to raid for parts).
-tony
10:18 a.m.
On Jun 16, 2015, at 06:54, tony duell <ard at
p850ug1.demon.co.uk> wrote:
As an aside, when I restore m 11/730 I am in 2 minds as to what to do about the microcode
load
device. a TU58 emulator is certainly convenient, but I actually would rather get the real
tape drives
working if at all possible. After all that is what the machine was designed to use.
I'll consider using my real TU58 drive instead of an emulator when I find a working
TU58 cartridge. So far, that is foreign to my experience. :(
I've cleaned up my drive and replaced the capstan rubber, and I think my drive is
probably just fine. The problem is the media, which in my opinion was a poor mechanical
design when new. I also thoroughly distrust the similar mechanism of the larger QIC
tapes.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
11:01 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
Sent: 16 June 2015 14:55
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: using new technology on old machines
computing means
Sure, the pre-manufactured boards can allow you
to prototype
quickly... but I think Tony is kind of bemoaning the loss of the "old
way" and I respect that ... I kind of miss it myself, even though I
wasn't there to experience it first-hand ...
It's also that this is the 'classic computers' list. To me, classic
rather more than just the hardware. It also covers the
design and
construction methods, technology and so on. And there seems to be
precious little of that in a modern microcontroller acting as a clock
oscillator.
I find it odd that people want to have a
lights-and-switches panel, but
are
prepared to totally adulterate the hardware of the
machine that drives it.
There sometimes isn't enough hardware to go round. I would like a front
panel for my SBC6120 but I don't think DEC built a machine with a 61xx chip
and a front panel...
the microcode load device. a TU58 emulator is
certainly convenient, but I
actually would rather get the real tape drives working if at all possible.
After
> all that is what the machine was designed to use.
think I had over 30 packing boxes of modern-ish
components and more of
valves and CRTs. Not counting the dozen or so boxes of PCBs (some to use,
some to raid for parts).
I have a good selection of TTL but I am not longer sure if it works. I think
a lot of NOS TTL has rotted internal connecting wire.
12:28 p.m.
It's also
that this is the 'classic computers' list. To me, classic
computing means
rather more than just the hardware. It also covers the design and
construction methods, technology and so on. And there seems to be
precious little of that in a modern microcontroller acting as a clock
oscillator.
There isn't., but some-times we have to compromise, and sometimes we choose
to compromise. I looked at the circuit of the M484 and I might not have the
parts in the parts box... .. its also a nasty hybrid design with DC biased NPN
and PNP transistors. I
find it ugly and can see it being a pig to debug, though it simulates fine
in LTspice...
I didn't find it that hard to basically understand in my head. After all, there
are only 4 transistors, and 2 of those are just an output buffer. Quite
why having both NPN and PNP transistors makes it harder to understand
I do not know.
I will leave the flames about Spice and simulation packages in general for
another day.
-tony
6:35 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
Sent: 16 June 2015 17:29
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: using new technology on old machines
I assume you mean M452 here, I can't find a reference to M484.
I did don't know where 484 came from
It's
also that this is the 'classic computers' list. To me, classic
computing means rather more than just the hardware. It also covers
the design and construction methods, technology and so on. And there
seems to be precious little of that in a modern microcontroller
acting as a clock oscillator.
There isn't., but some-times we have to compromise, and sometimes we
choose to compromise. I looked at the circuit of the M484 and I might
not have the parts in the parts box...
I suspect many of the parts are not that critical.
I don't think so either, but I see from:-
http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/m/m452.pd
f
that the original appears to use a 2k 10-turn pot, and a 7440 output buffer,
neither of which are in my rather extensive junk box.
In fact the 7440 are rather rare, and I see the cheapest I can get them for
is around $4.00 each.
I do however have a tube of pic 16f84 chips and a few 4Mhz crystals and so
could build a suitable generator with 1 x IC and 1 xtal.
The great thing about PIC, Arduino and FPGA is they allow the creation of
something which is as functionally identical to the original as you can get
without duplicating it.
.. its also a
nasty hybrid design with DC biased NPN and PNP
transistors. I find it ugly and can see it being a pig to debug,
though it simulates fine in LTspice...
I didn't find it that hard to basically understand in my head. After all,
are only 4 transistors, and 2 of those are just an
output buffer. Quite
why
having both NPN and PNP transistors makes it harder to
understand I do not
know.
I am really used to RF circuits so am puzzled there is no inductor. It kind
of looks like a Darlington Pair but it isn't.
What I don't understand is why the emitter of Q1 is spliced in what I assume
is a voltage divider in the collector of q2.
I was expecting a multivibrator circuit...
I will leave the flames about Spice and simulation packages in general for
another day.
You are touchy. Would it help if I used the original Spice2 written in
Fortran IV. It still works. Sadly I don't have a real mainframe but have to
use Hercules to run it....
-tony
Dave
17 Jun
17 Jun
12:29 a.m.
[M452]
OK, I sort-of forgot the smiley, but only sort-of.
The problem is that people try to understand a circuit by throwing it on the
simulator and really don't understand what is going on at all (this assumes
the simulator gets it right which is not always the case). I prefer to think about
it. work out how the capacitor (there is only one!) charges and discharges, since
that must be the key to the oscillations.
-tony
that the original appears to use a 2k 10-turn pot, and
a 7440 output buffer,
neither of which are in my rather extensive junk box.
In fact the 7440 are rather rare, and I see the cheapest I can get them for
is around $4.00 each.
True. But you don't need either to build and test the oscillator circuit. The 7440 is
an output buffer, if you want to build a test version of the entire module you could
stick a '20 there or just about any other TTL inverting gate. But I was thinking of
just
testing the oscillator part which is Q1 and Q2 (again the other 2 transistors are
buffers)
The preset clearly sets the frequency. You could build the oscillator with say a 1k
resistor there at least to put a 'scope on various points to understand how it works.
I am really used to RF circuits so am puzzled there is
no inductor. It kind
of looks like a Darlington Pair but it isn't.
RC oscillators have been around since the 1930s.....
I will leave
the flames about Spice and simulation packages in general for
another day.
You are touchy. Would it help if I used the original Spice2 written in
Fortran IV. It still works. Sadly I don't have a real mainframe but have to
use Hercules to run it.... 
4:12 a.m.
On 2015-Jun-16, at 3:35 PM, Dave G4UGM wrote:
there
I think you could characterise it as:
- Q1 & Q2 form a two-stage direct-coupled non-inverting amplifier from Q1-B to Q2-C.
- C5, the main timing cap, is thus effectively in AC positive feedback, as one would
expect for an oscillator.
- R9 (the R between Q2-C and Q1-E you were questioning) provides DC negative feedback,
presumably to help stabilise and fix the circuit characteristics, as some measure of
stability is going to be
needed for a baud-rate generator. Note it also has it's own voltage regulator in D1
to D4.
At first glance I thought R9 might be there to provide some hysteresis in the switching
thresholds for the RC charge/discharge but it looks like it acts in the opposite direction
to that.
The base circuit of Q3 (the first stage of buffering) will draw current from the
high-impedance side (R8,R9) of the oscillator output, pulling up the C5,R9 junction when
Q2 is off, so it will probably affect the oscillator and be necessary to get the
'proper' functioning of the oscillator portion of the circuit.
-----Original
Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
.. its
also a nasty hybrid design with DC biased NPN and PNP
transistors. I find it ugly and can see it being a pig to debug,
though it simulates fine in LTspice...
I didn't find it that hard to basically understand in my head. After all, are only 4 transistors, and 2 of those are just
an output buffer. Quite
why
having both NPN and PNP transistors makes it
harder to understand I do not
know.
I am really used to RF circuits so am puzzled there is no inductor. It kind
of looks like a Darlington Pair but it isn't.
What I don't understand is why the emitter of Q1 is spliced in what I assume
is a voltage divider in the collector of q2.
I was expecting a multivibrator circuit...
4:27 a.m.
The M452 module schematic for quick access for anyone following along, as it hasn't
been linked before in the thread:
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/modules/mSeries/M452.p…
6:55 a.m.
That's only the schematic. The link I included earlier:-
http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/m/m452.pd
f
also includes the PCB component layout, from which I inferred the Trim Pot
is of the 10-turn variety.
Dave
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: 17 June 2015 09:28
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: using new technology on old machines
The M452 module schematic for quick access for anyone following along, as
it
hasn't been linked before in the thread:
http://bitsavers.informatik.uni-
stuttgart.de/pdf/dec/modules/mSeries/M452.pdf
10:38 a.m.
Whoops, sorry for not noting that, a link had not been included earlier in the thread so I
had had to search it out.
On 2015-Jun-17, at 3:55 AM, Dave G4UGM wrote:
That's only the schematic. The link I included
earlier:-
http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/m/m452.pd
f
also includes the PCB component layout, from which I inferred the Trim Pot
is of the 10-turn variety.
Dave
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: 17 June 2015 09:28
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: using new technology on old machines
The M452 module schematic for quick access for anyone following along, as
it
hasn't been linked before in the thread:
http://bitsavers.informatik.uni-
stuttgart.de/pdf/dec/modules/mSeries/M452.pdf
7:28 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: 17 June 2015 09:13
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: using new technology on old machines
On 2015-Jun-16, at 3:35 PM, Dave G4UGM wrote:
there
I think you could characterise it as:
- Q1 & Q2 form a two-stage direct-coupled non-inverting amplifier
from Q1-B to Q2-C.
- C5, the main timing cap, is thus effectively in AC positive
feedback,
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
.. its
also a nasty hybrid design with DC biased NPN and PNP
transistors. I find it ugly and can see it being a pig to debug,
though it simulates fine in LTspice...
I didn't find it that hard to basically understand in my head. After
all, are only 4 transistors, and 2 of those are just
an output buffer.
Quite
why
having both NPN and PNP transistors makes it
harder to understand I
do not know.
I am really used to RF circuits so am puzzled there is no inductor. It
kind of looks like a Darlington Pair but it isn't.
What I don't understand is why the emitter of Q1 is spliced in what I
assume is a voltage divider in the collector of q2.
I was expecting a multivibrator circuit... as one would expect for an oscillator.
- R9 (the R between Q2-C and Q1-E you were questioning) provides
DC negative feedback,
presumably to help stabilise and fix the circuit characteristics,
as
some measure of stability is going to be
needed for a baud-rate generator. Note it also has it's own
voltage
regulator in D1 to D4.
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.....
At first glance I thought R9 might be there to provide
some hysteresis in
the
switching thresholds for the RC charge/discharge but
it looks like it acts
in the
opposite direction to that.
The base circuit of Q3 (the first stage of buffering) will draw current
from the
high-impedance side (R8,R9) of the oscillator output, pulling up the C5,R9
junction when Q2 is off, so it will probably affect the oscillator and be
necessary to get the 'proper' functioning of the oscillator portion of the
circuit.
I included that in my LTSpice model....
... but it doesn't actually have that much effect...
Dave
G4UGM
5:14 p.m.
On 2015-06-17 13:28, Dave G4UGM wrote:
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.
While the cap charges, it steals the base current which
would otherwise
have gone to Q1, thus keeping Q1 turned off. When the cap nears the end
of the charge, more current goes to the base of Q1 which turns on,
turning on Q2, which raises the voltage over R8 and R9. Since the
voltage on a capacitor cannot change instantaneously, the voltage on the
base of Q1 rises while the cap discharges through the base of Q1,
keeping it hard on. As the cap discharges and charges in the reverse
direction, the base current of Q1 decreases and ultimately Q1 turns off,
turning off Q2 and lowering the voltage over R8 and R9, and the cycle
starts over.
For the circuit to work, I think (I may be wrong) the base current
supplied to Q1 by R5 and the pot has to be not quite sufficient to turn
it on. Also the cap is reverse charged for one half cycle.
I believe this is a classical astable multivibrator circuit, but not the
more common one with two cross-coupled transistors with capacitors from
the collector of one to the base of the other. The DEC circuit I think
can be seen a lot in old Siemens application books from the 1960s, such
as may be found here (note German books):
http://rainers-elektronikpage.de/SIEMENS-Fach---u_-Datenbucher/siemens-fach…
/Jonas
At this point the cap is then charged (or discharged) in the reverse
direction via Q2, D5 and R4 until Q1 turns off.....
At first glance I thought R9 might be there to
provide some hysteresis in
the
switching thresholds for the RC charge/discharge
but it looks like it acts
in the
opposite direction to that.
The base circuit of Q3 (the first stage of buffering) will draw current
from the
high-impedance side (R8,R9) of the oscillator
output, pulling up the C5,R9
junction when Q2 is off, so it will probably affect the oscillator and be
necessary to get the 'proper' functioning of the oscillator portion of the
circuit.
I included that in my LTSpice model....
... but it doesn't actually have that much effect...
Dave
G4UGM
16 Jun
16 Jun
11:58 a.m.
On Tue, Jun 16, 2015 at 01:54:56PM +0000, tony duell wrote:
I find it odd that people want to have a lights-and-switches panel, but are prepared to
totally
adulterate the hardware of the machine that drives it.
Are you honestly suggesting that I should rebuild a PDP-11/70
from things I have in my partsbin?
'cause that is what it sounds like.
/P
11:58 a.m.
I find it odd that people want to have a lights-and-switches panel, but are prepared to
totally
adulterate the hardware of the machine that drives it.
Are you honestly suggesting that I should rebuild a PDP-11/70
from things I have in my partsbin? 'cause that is what it sounds like.
No, not really. If you have a front panel from an otherwise non-existant machine then
it makes sense to drive it any way you can. I was thinking more of the PDP12 that started
this.
-tony
12:04 p.m.
On Tue, Jun 16, 2015 at 03:58:51PM +0000, tony duell wrote:
Oh, very much! Then we could have a discussion about using
modern switching power supplies ot not ;-)
/P
Are you
honestly suggesting that I should rebuild a PDP-11/70
from things I have in my partsbin?
You have to admit it would be an interesting and educational
project :-)
12:24 p.m.
On Tue, Jun 16, 2015 at 04:18:03PM +0000, tony duell wrote:
[Build your own 11/70]
I would suspect that modern switchers are more efficient. If I
wanted to have one running for any longer extent I would
consider an "upgrade". Only reversible changes of course.
/P
Oh, very much! Then we could have a discussion
about using
modern switching power supplies ot not ;-)
As opposed to the original 11/70 switching supply?
12:25 p.m.
Oh, very
much! Then we could have a discussion about using
modern switching power supplies ot not ;-)
As opposed to the original 11/70 switching supply? 
3:32 p.m.
On Tue, 16 Jun 2015, tony duell wrote:
Quite probably, but the modern mains-side switcher is
more
troublesome and a lot less pleasant to repair. I think I'll stick
with the room-heater in my 11's :-)
Well, you could use a switcher, paralleled to the mains with a heater.
Just as you can use a CFL along with a heater for some applications
that call for an incandescent.
3:41 p.m.
Quite
probably, but the modern mains-side switcher is more
troublesome and a lot less pleasant to repair. I think I'll stick
with the room-heater in my 11's :-)
Well, you could use a switcher, paralleled to the mains with a heater. Just as you can use a CFL along with a heater for some
applications
that call for an incandescent.
I once saw a curious lightbulb which contained both a mercury vapour
discharge lamp and a filament. The idea was that the latter would
provide some red light to go along with the predominantly
blue/green mercury lamp. I think the filament was also the ballast
for the dischage lamp.
Oh well.. The time I need a filament lamp is when I am using it for
the electrical characteristics (e.g. using it as a ballast resistor),
so no kludge with a CFL is likely to work
-tony
4:05 p.m.
On Jun 16, 2015 3:43 PM, "tony duell" <ard at p850ug1.demon.co.uk> wrote:
Actually, no. That honour goes to the PSU in a Zenith MDA monitor
which as I said 'combines the efficiency of a linear with the reliability
of a switcher'. The design (if you can call it that) of this PSU is to
rectify the mains, feed it into a free-running chopper circuit, then
a transformer. The output of that is half-wave (!) rectified giving
about 18V DC. Note the chopper free-runs, so there is no regulation
applied at this point. That 18V is then fed to a discrete-transistor
linear regulator.
And that's not the end of the 'curious' design. As you know, a linear
regualtor compares the output voltage of the supply with a
reference votlage. That reference voltage is typically produced by
a zener diode. Not in this monitor. It uses the drop across the
power-on LED. Which means it is important to use a green LED.
Another colour, with a different Vf, and the PSU output is wrong.
I would love to have a copy of that schematic for an Engineering Wall of
Shame. Seriously, that is the strangest supply design I've ever heard.
Kyle
8:49 p.m.
On Jun 16, 2015, at 4:05 PM, Kyle Owen <kylevowen
at gmail.com> wrote:
On Jun 16, 2015 3:43 PM, "tony duell" <ard at p850ug1.demon.co.uk>
wrote:
>
> Actually, no. That honour goes to the PSU in a Zenith MDA monitor
> which as I said 'combines the efficiency of a linear with the reliability
> of a switcher'. The design (if you can call it that) of this PSU is to
> rectify the mains, feed it into a free-running chopper circuit, then
> a transformer. The output of that is half-wave (!) rectified giving
> about 18V DC. Note the chopper free-runs, so there is no regulation
> applied at this point. That 18V is then fed to a discrete-transistor
> linear regulator.
Maybe someone learned how high voltage supplies for TV sets work (from the sweep voltage)
and decided to apply that. It does sound like someone with too little knowledge or
ability for the job.
And that's not the end of the 'curious' design. As you know, a linear
regualtor compares the output voltage of the supply with a
reference votlage. That reference voltage is typically produced by
a zener diode. Not in this monitor. It uses the drop across the
power-on LED. Which means it is important to use a green LED.
Another colour, with a different Vf, and the PSU output is wrong.
I would love to have a copy of that schematic for an Engineering Wall of
Shame. Seriously, that is the strangest supply design I've ever heard.
17 Jun
17 Jun
12:14 a.m.
Actually, no. That honour goes to the PSU in a Zenith MDA monitor
which as I said 'combines the efficiency of a linear with the reliability
of a switcher'. The design (if you can call it that) of this PSU is to
rectify the mains, feed it into a free-running chopper circuit, then
a transformer. The output of that is half-wave (!) rectified giving
about 18V DC. Note the chopper free-runs, so there is no regulation
applied at this point. That 18V is then fed to a discrete-transistor
linear regulator.
And that's not the end of the 'curious' design. As you know, a linear
regualtor compares the output voltage of the supply with a
reference votlage. That reference voltage is
typically produced by
a zener diode. Not in this monitor. It uses the drop across
the
power-on LED. Which means it is important to use a green LED.
Another colour, with a different Vf, and the PSU output is wrong. I would love to have a copy of that schematic for an
Engineering Wall of
Shame. Seriously, that is the strangest supply design I've ever heard.
I don't know if it was ever published [1], but I should have a reverse-engineered
version somewhere. When I unpack it (after the move...) I will see about getting
it scanned. It really is a crazy design.
[1] There was the standard 'safety component' warning telling you only to use
the parts specified in the service manual on the back cover. But I was totally
unable to obtain said service manual.
-tony
16 Jun
16 Jun
1:10 p.m.
On 6/16/2015 9:58 AM, Pontus Pihlgren wrote:
On Tue, Jun 16, 2015 at 01:54:56PM +0000, tony duell
wrote:
I was more expecting a PDP 8 :)
Ben.
I find it odd that people want to have a lights-and-switches panel, but are prepared to
totally
adulterate the hardware of the machine that drives it.
Are you honestly suggesting that I should rebuild a PDP-11/70
from things I have in my partsbin?
'cause that is what it sounds like.
/P
8:52 p.m.
On Wed, Jun 17, 2015 at 1:54 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
It's also that this is the 'classic
computers' list. To me, classic computing means rather
more than just the hardware. It also covers the design and construction methods,
technology
and so on.
DING.
Staying slightly on-topic, working on serious wire-wrap backplanes can
get a bit hairy. We probably all have hand-wrapping tools, and can do
the occasional repair or patch as required. But...
'remanufacturing' has become part of preservation movements in
general; 'preservation/re-creation' might be a better name. The
ultimate example of this might be from the railway world. A famous
class of British steam locomotives - the A1 Pacific - had become
extinct; all were scrapped before railway preservation really became a
Big Thing. So, enough enthusiasts got together and they *built* one.
From scratch, from raw metal: http://www.a1steam.com
There are various bits of DEC hardware that are extinct, or in
critically short supply. I would love to have a TC15 DECtape
controller for my pdp-15s; fat chance of ever finding one. Ditto for
memory for my KL10. Oh sure, we can make modern functionally
equivalent replacements, like Guy S, LCM etc, have done. But it's not
the same...
DEC backplanes were largely wire-wrapped by machine; I've seen
pictures. If the interest was there, it should be possible to restore
or re-create the machines used by DEC to manufacture backplanes. From
there, it's a relatively small step to source, or manufacture new
batches of, the modules etc. needed to populate them
Has this ever been seriously considered, or mooted as a possible
co-operative venture for a group of us?
Mike
http://www.corestore.org
'No greater love hath a man than he lay down his life for his brother.
Not for millions, not for glory, not for fame.
For one person, in the dark, where no one will ever know or see.'
9:49 p.m.
On Jun 16, 2015, at 17:52 , Mike Ross <tmfdmike at
gmail.com> wrote:
'remanufacturing' has become part of preservation movements in
general;
[...]
Has this ever been seriously considered, or mooted as
a possible
co-operative venture for a group of us?
On this topic, I'm particularly curious about remanufacturing of consumables such as
magnetic media, printer ribbons, etc. Not only are supplies of unused consumables
monotonically decreasing, but even remaining ones are succumbing to shelf rot (case in
point: TU58 cartridges, and particularly their drive belts).
In many cases, it may not be strictly necessary to manufacture the entire item. For a TU58
cartridge, the baseplate, case, reels, etc. may be quite usable. The tape probably needs
to be replaced, but maybe a particular formulation of common audio tape could be used
instead of manufacturing tape from scratch. The belts would certainly need to be
manufactured from scratch.
In other cases, even where the item needs to be manufactured from scratch, might it be
acceptable to use modern methods to manufacture authentic-ish replacement consumables? If
somebody figured out how to create suitable magnetic material and binder for floppy disk
media and apply it to mylar sheets, for example, maybe a laser cutter could be used to cut
out various kinds of blanks (5.25", 8", soft-sectored, various hard-sectored
configurations) without the tooling cost of punching dies that would make more sense for
mass production?
Would the mentioned automatic wire-wrapping machine need to be recreated in a
period-correct manner, or would it be acceptable to make one using modern expedient
hardware in order to use it to create new authentic reproductions?
What sort of concessions could we accept for the lack of authentic components to be used?
In the case of a locomotive, there are an awful lots of parts that could be authentically
remanufactured in a regular machine shop (obviously, large forgings and the like would be
more challenging!). But in the case of a computer using particular no-longer-manufactured
semiconductor components, the thought of bringing up a suitable semiconductor fab to build
those components would be economically unrealistic.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
17 Jun
17 Jun
2:47 a.m.
On Wed, Jun 17, 2015 at 12:52:23PM +1200, Mike Ross wrote:
Has this ever been seriously considered, or mooted as a possible
co-operative venture for a group of us?
I see it on the small scale all the time. Such as Rod's new front panels
for the 8/e. Or the various replica kits for early micros.
One computer I could imagine would sparc interest is a new PDP-6. Not
sure how that would materialise.
I have a theory as to why it hasn't happened yet though. And that is
lack of skill. Take an average sized Swedish town and you can probably
scrounge up a fair amount of welders, carpenters, painters and
metalworkers willing to work on a fun medium to large scale project such
as restoring trains, cars and even whole factories. And given the number of
"industry heritage" museums in Sweden it's a fairly big group.
But finding the a good sized group of people with the right skills for
wirewrapping a large scale backplane and populating it with period
correct hardware... much harder I think.
There are other problems too, finding a big chunk of metal to machine a
new crankshaft is not so hard. Where do you find enough germanium
transistors for a PDP-6 (I'm guessing that is what was used, and I'm
also guessing that they are less common today, please correct me if I'm
wrong)
I would love to work on such a project though!
/P
16 Jun
16 Jun
12:40 a.m.
I could
replace an M1 Carbine trigger spring on the spot, or a HMMWV
taillamp housing ... Should I criticize you for not having SAE grade 8
hardware on hand, or Bristo wrenches
I think Tony's point was that someone who's into vintage computers ought to
have a stock of suitable parts for them.
So unless he's into older guns, or cars, were he not to have things like SAE
8 hardware around, that would be understandable - he doesn't do them. Having said that, _I_ don't have 2N3904s nor
NE555s around either! I do have
a modest number of parts (e.g. 4164's, 40-ping Berg shells, .250 tab
hardware, etc, etc) - a large enough collection that I just had to
re-organize and add more parts holders (although that was mostly because I
went berserk at the local Radio Shack in the 80% off sale). But it takes a
long time to build up a really comprehensive collection of parts.
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.
-tony
1:03 a.m.
On Jun 15, 2015, at 21:40, tony duell <ard at
p850ug1.demon.co.uk> wrote:
Exactly. I don't do firearms at all (we have various IMHO ridiculous laws in the UK,
but I do not want to start that debate)
Sorry I even brought it up; I was just using it as an example of the different
specializations that each person might wallow in. Guns, religion, politics and text editor
preference are often too contentious to discuss in polite company. :)
But if you are going to repair/restore something then
IMHO it makes a lot of
sense to have common spares around.
Agreed! But you generally tend to accumulate those spares *after* you have been involved
in that particular area for a while. Coming into it from scratch, you might not even know
which parts you're most likely to need. And buying every common-ish part that you
might need is an expensive proposition.
But common TTL parts, transistors, etc are used in
many
machines, and if you are going to restore the real hardware you are (a) going
to need them and (b) are going to need to now how they work so you can
trace faults.
Right. So coming in from scratch, you might buy a tube of 74LS00 instead of just the one
that you need to fix one board, and so on for many other common parts.
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.
Agreed again! For example, the first time I had a Rifa paper-dielectric EMI filtering cap
go incandescent on me (happened to be in a Tandy Model 12), I figured out the three or
four kinds of much better poly film EMI filtering caps I'd need to replace them on
sight in the Astec supplies that Tandy stuck in everything, and I bought lots of extras.
But I don't have a single 2N3904 in my junk box, because I don't think I've
had to replace one in the last 30 years, just based on the kinds of things I've been
working on. So it's not my go-to part. Now, 10k resistors and 0.1uF ceramic caps...
those things I use a lot. :)
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
1:07 a.m.
But if you are going to repair/restore something
then IMHO it makes a lot of
sense to have common spares around.
Agreed! But you generally tend to accumulate those spares *after* you have been involved
in that particular area for a while. Coming into it from scratch, you
might not even know which parts you're most likely to need.
And buying every common-ish part that you might need is an expensive proposition.
That is also true. And it's not obvious what is common and it very much depends on the
machine you
are working on. If you fix 1980s home micros you probably have a few 6502 and Z80s
on-hand, but they
are not a lot of use in a PDP12.
[...]
extras. But I don't have a single 2N3904 in my
junk box, because I don't think I've had to replace one in the last
I use them all the time for LED drivers, etc....
30 years, just based on the kinds of things I've
been working on. So it's not my go-to part. Now, 10k resistors
and 0.1uF ceramic caps... those things I use a lot. :)
And to get back to that darn M452 module that started this, it is _precisely_ those sort
of R's and C's you need
to change its frequency!
-tony
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
3324
days inactive
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33 comments
14 participants
participants (14)
-
ard＠p850ug1.demon.co.uk -
bfranchuk＠jetnet.ab.ca -
cisin＠xenosoft.com -
dave.g4ugm＠gmail.com -
fozztexx＠fozztexx.com -
hilpert＠cs.ubc.ca -
jnc＠mercury.lcs.mit.edu -
jonas＠otter.se -
kylevowen＠gmail.com -
nf6x＠nf6x.net -
paulkoning＠comcast.net -
pontus＠Update.UU.SE -
scaron＠umich.edu -
tmfdmike＠gmail.com