15 Apr
2009
15 Apr
'09
6:37 p.m.
With the recent discussions of the PDP-11/20, I've been thinking of
what all I'll need to gather to restore mine. It's been a long time
since I pulled things from the pile, but I'm pretty sure that before
it was pitched, the fans and PSUs were harvested.
I've found pictures on the 'net of the fans - looking at the wiring,
they appear to me to be pretty standard 110VAC boxer fans. ISTR
hearing that the fans in the 11/40 or 11/45 are bizarre, but I'm
expecting that the fans in the 11/20 are ordinary. This leaves the
PSUs. If I were going to go with MOS memory, I wouldn't worry about
what to use - the Unibus itself only needs to provide +5V, and +/-15V.
Because the 11/20 routinely held core, it's expecting +8V (unreg)
plus -22V on top of the usual voltages.
Since the "easiest" solution is to get the original equipment
reattached, I'm curious how much an H720 might fetch these days. If
it's too much, I can always come up with some other way to provide
power to run core (or skip the core and use MOS).
My question for those that have tried recently, is it feasible to go
searching for 1-3 H720 PSUs, or are they old enough that the chances
of running across them are slim enough to make building a functional
replacement a preferable go (preferable from the standpoint of ever
being able to finish).
Thanks,
-ethan
15 Apr
15 Apr
4:25 p.m.
I've found pictures on the 'net of the fans -
looking at the wiring,
they appear to me to be pretty standard 110VAC boxer fans. ISTR
hearing that the fans in the 11/40 or 11/45 are bizarre, but I'm
The fans in an 11/45 are plain 110V ones (even in the UK, they're run off
the primary of the mains transformer acting as an autotransformer). I
suspect the 11/40 is the same.
It's the 11/44 (a much later machine) that has odd fans -- 35V 70Hz or
something. They run off a transistorised full-H driver circuit in the
PSU, so they can be run off the backup battery.
expecting that the fans in the 11/20 are ordinary.
This leaves the
PSUs. If I were going to go with MOS memory, I wouldn't worry about
what to use - the Unibus itself only needs to provide +5V, and +/-15V.
Because the 11/20 routinely held core, it's expecting +8V (unreg)
plus -22V on top of the usual voltages.
You may find that +8V is used eleewhere. I remember a +8V supply for the
lamps on the KM11, and it may be used by the front panel lamps.
-tony
8:28 p.m.
On Wed, Apr 15, 2009 at 12:25 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
OK.
Good point. I don't know the 11/20 inside and out, but I do know my
way around the PDP-8/e, and the lamps on the front panel don't run off
the +5V on the Omnibus (there's a PSU lead right to spade connectors
on the front panel).
OK. So... that makes finding at least one H720 more important.
Thanks for the info.
-ethan
I've found
pictures on the 'net of the fans - looking at the wiring,
they appear to me to be pretty standard 110VAC boxer fans. ?ISTR
hearing that the fans in the 11/40 or 11/45 are bizarre, but I'm
The fans in an 11/45 are plain 110V ones (even in the UK, they're run off
the primary of the mains transformer acting as an autotransformer). I
suspect the 11/40 is the same. It's the 11/44 (a much later machine) that has odd
fans -- 35V 70Hz or
something. They run off a transistorised full-H driver circuit in the
PSU, so they can be run off the backup battery.
That's the one. I guess I should have paid more attention - I have an
11/44, but I've never fiddled with the fans. I think I'll put "check
and clean 11/44 fans" on the list of summer classiccmp tasks.
... If I were
going to go with MOS memory, I wouldn't worry about
what to use - the Unibus itself only needs to provide +5V, and +/-15V.
?Because the 11/20 routinely held core, it's expecting +8V (unreg)
plus -22V on top of the usual voltages.
You may find that +8V is used eleewhere. I remember a +8V supply for the
lamps on the KM11, and it may be used by the front panel lamps.
16 Apr
16 Apr
6:14 p.m.
It's the
11/44 (a much later machine) that has odd fans -- 35V 70Hz or
something. They run off a transistorised full-H driver circuit in the
PSU, so they can be run off the backup battery.
That's the one. I guess I should have paid more attention - I have an
11/44, but I've never fiddled with the fans. I think I'll put "check
and clean 11/44 fans" on the list of summer classiccmp tasks.
OK. So... that makes finding at least one H720 more important.
I have at least 2 of them, but neither are spare (not to mention the fact
that (a) they're the 230V version and (b) shipping would be expensive).
One runs the RK11C on my 11/45 system. The other is part of a DX11 which
I really must get round to investigating.
-tony
3:22 p.m.
On Wednesday 15 April 2009 12:25:53 pm Tony Duell wrote:
I have some power supplies -- out of an IBM storage setup or similar -- that
use fans that operate on an odd voltage like that. I get the impression that
they chose that voltage as being the maximim input for some 3-terminal
regulator part on the other end.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
I've found
pictures on the 'net of the fans - looking at the wiring,
they appear to me to be pretty standard 110VAC boxer fans. ISTR
hearing that the fans in the 11/40 or 11/45 are bizarre, but I'm
The fans in an 11/45 are plain 110V ones (even in the UK, they're run off
the primary of the mains transformer acting as an autotransformer). I
suspect the 11/40 is the same.
It's the 11/44 (a much later machine) that has odd fans -- 35V 70Hz or
something. They run off a transistorised full-H driver circuit in the
PSU, so they can be run off the backup battery. expecting that
the fans in the 11/20 are ordinary. This leaves the
PSUs. If I were going to go with MOS memory, I wouldn't worry about
what to use - the Unibus itself only needs to provide +5V, and +/-15V.
Because the 11/20 routinely held core, it's expecting +8V (unreg)
plus -22V on top of the usual voltages.
You may find that +8V is used eleewhere. I remember a +8V supply for the
lamps on the KM11, and it may be used by the front panel lamps.
-tony
6:44 p.m.
It's the
11/44 (a much later machine) that has odd fans -- 35V 70Hz or
something. They run off a transistorised full-H driver circuit in the
PSU, so they can be run off the backup battery.
I have some power supplies -- out of an IBM storage setup or similar -- that
use fans that operate on an odd voltage like that. I get the impression that
they chose that voltage as being the maximim input for some 3-terminal
regulator part on the other end. 
18 Apr
18 Apr
7:22 p.m.
On Thu, 2009-04-16 at 19:44 +0100, Tony Duell wrote:
I thought welders typically used tens of volts...
But I haev no intention of short-circuiting my 11/44 PSU to see if I can
weld a screwdriver to the terminals.
-tony
The second one provides the +5V (at 125A or
something)
That's a MIG welder, Tony... 
8:01 p.m.
The second one provides the +5V (at 125A or something)
That's a MIG welder, Tony... 
15 Apr
15 Apr
7:35 p.m.
Date: Wed, 15 Apr 2009 14:37:39 -0400
Subject: H720 PSU?
From: ethan.dicks at gmail.com
To: cctalk at classiccmp.org
With the recent discussions of the PDP-11/20, I've been thinking of
what all I'll need to gather to restore mine. It's been a long time
since I pulled things from the pile, but I'm pretty sure that before
it was pitched, the fans and PSUs were harvested.
I've found pictures on the 'net of the fans - looking at the wiring,
they appear to me to be pretty standard 110VAC boxer fans. ISTR
hearing that the fans in the 11/40 or 11/45 are bizarre, but I'm
expecting that the fans in the 11/20 are ordinary.
I could check in a week or so, but others on this list can probably
beat me to it :-) Regarding weird fans, you got it almost correct Ethan.
The 11/40 has standard 110 VAC fans (I'm sure of that), and again, in a
week or so I can tell what's in the 11/45. It is the 11/44 that has the
"odd" fans. IIRC, they are 35V, 70 Hz models!
Since the "easiest" solution is to get the
original equipment
reattached, I'm curious how much an H720 might fetch these days. If
it's too much, I can always come up with some other way to provide
power to run core (or skip the core and use MOS).
My question for those that have tried recently, is it feasible to go
searching for 1-3 H720 PSUs, or are they old enough that the chances
of running across them are slim enough to make building a functional
replacement a preferable go (preferable from the standpoint of ever
being able to finish).
I bought the 11/20 from a chap here in Holland, and he told me that he
stored an 11/20 spare PSU in the storage space of somebody else. I had
to go myself after that PSU, but I have not yet done that. Not having
checked, I carefully say that if you have an H720 and it goes defective,
it will be easy to repair (besides the transformer, I guess).
If I get that spare PSU (if it is not yet scrapped), and the PSU in my
11/20 turns out to be OK, I might sell the other PSU, but I am afraid
that shipping cost to the USA would be huge ...
- Henk.
(wishing days were 36 hours long)
5737
days inactive
5740
days old
10 comments
7 participants
participants (7)
-
alexandre-listas＠e-secure.com.br -
ard＠p850ug1.demon.co.uk -
ethan.dicks＠gmail.com -
gordonjcp＠gjcp.net -
henk.gooijen＠hotmail.com -
lists＠databasics.us -
rtellason＠verizon.net