17 Sep
2018
17 Sep
'18
11:18 a.m.
From: Pierre Gebhardt
two H745 bricks (delivering -15V) which are still
missing. I'd be very
happy, if anybody could consider parting with one or two. Location is
in Germany.
There should be some on eBait; mildly expensive, but if you get them from
the US, the shipping is going to be a fair amount anyway...
Noel
17 Sep
17 Sep
11:54 a.m.
Hello Noel,
thanks for your quick reply. There are indeed some DEC power brick models on epay, but
none regarding the H745.
All the best,
Pierre
? ? > From: Pierre Gebhardt
? ? > two H745 bricks (delivering -15V) which are still missing. I'd be very
? ? > happy, if anybody could consider parting with one or two. Location is
? ? > in Germany.
There should be some on eBait; mildly expensive, but if you get them from
the US, the shipping is going to be a fair amount anyway...
??? Noel
12:05 p.m.
H745's are harder to find. I have at least one that needs service but I am
located in the USA and I have no clear idea what's wrong with it. Is it
that you have zero h745's at all or you have a bad one? Is there a typical
point of failure for these? If so, I'd try to track down a bad one and fix
it. Probably a lot cheaper.
b
On Mon, Sep 17, 2018 at 2:54 PM P Gebhardt via cctalk <cctalk at classiccmp.org>
wrote:
Hello Noel,
thanks for your quick reply. There are indeed some DEC power brick models
on epay, but none regarding the H745.
All the best,
Pierre
From: Pierre Gebhardt
two H745 bricks (delivering -15V) which are still
missing. I'd be
very
happy, if anybody could consider parting with one
or two. Location is
in Germany.
There should be some on eBait; mildly expensive, but if you get them from
the US, the shipping is going to be a fair amount anyway...
Noel
12:07 p.m.
here is a photo of some of the failed regulators I have on hand that I have
pulled from production over the years:
https://pbs.twimg.com/media/DML8O8dW0AISX5m.jpg
On Mon, Sep 17, 2018 at 3:05 PM Bill Degnan <billdegnan at gmail.com> wrote:
H745's are harder to find. I have at least one
that needs service but I
am located in the USA and I have no clear idea what's wrong with it. Is it
that you have zero h745's at all or you have a bad one? Is there a typical
point of failure for these? If so, I'd try to track down a bad one and fix
it. Probably a lot cheaper.
b
On Mon, Sep 17, 2018 at 2:54 PM P Gebhardt via cctalk <
cctalk at classiccmp.org> wrote:
Hello Noel,
thanks for your quick reply. There are indeed some DEC power brick models
on epay, but none regarding the H745.
All the best,
Pierre
From: Pierre Gebhardt
two H745 bricks (delivering -15V) which are still
missing. I'd be
very
happy, if anybody could consider parting with one
or two. Location
is
in Germany.
There should be some on eBait; mildly expensive, but if you get them from
the US, the shipping is going to be a fair amount anyway...
Noel
3:17 p.m.
I had a problem with brick power supplies a number of years back. I found an issue that
caused them to fail. I had about ten of them on the same power switch. You'd think
this would not be an issue but it is.
You see it works like this, each one had a transformer in it. When you disconnect the
power, with a switch, each of the transformers often has energy left in the cores.
Normally for just one supply, this isn't an issue. When you have a bunch of these,
only one supply absorbs all of the energy. When it does, it will blow some part of that
supply up. On the ones I had, it'd take of the negative rail.
I put a MOV on the power rail and didn't have any more issues with power cycling.
Dwight
________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Bill Degnan via cctalk
<cctalk at classiccmp.org>
Sent: Monday, September 17, 2018 12:07:22 PM
To: p.gebhardt at ymail.com; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Looking for two DEC H445 power bricks for PDP 11/40 project
here is a photo of some of the failed regulators I have on hand that I have
pulled from production over the years:
https://pbs.twimg.com/media/DML8O8dW0AISX5m.jpg
On Mon, Sep 17, 2018 at 3:05 PM Bill Degnan <billdegnan at gmail.com> wrote:
H745's are harder to find. I have at least one
that needs service but I
am located in the USA and I have no clear idea what's wrong with it. Is it
that you have zero h745's at all or you have a bad one? Is there a typical
point of failure for these? If so, I'd try to track down a bad one and fix
it. Probably a lot cheaper.
b
On Mon, Sep 17, 2018 at 2:54 PM P Gebhardt via cctalk <
cctalk at classiccmp.org> wrote:
Hello Noel,
thanks for your quick reply. There are indeed some DEC power brick models
on epay, but none regarding the H745.
All the best,
Pierre
From: Pierre Gebhardt
two H745 bricks (delivering -15V) which are still
missing. I'd be
very
happy, if anybody could consider parting with one
or two. Location
is
in Germany.
There should be some on eBait; mildly expensive, but if you get them from
the US, the shipping is going to be a fair amount anyway...
Noel
3:49 p.m.
On Mon, Sep 17, 2018 at 4:17 PM, dwight via cctalk <cctalk at classiccmp.org>
wrote:
I had a problem with brick power supplies a number of
years back. I found
an issue that caused them to fail. I had about ten of them on the same
power switch. You'd think this would not be an issue but it is.
You see it works like this, each one had a transformer in it. When you
disconnect the power, with a switch, each of the transformers often has
energy left in the cores. Normally for just one supply, this isn't an
issue. When you have a bunch of these, only one supply absorbs all of the
energy. When it does, it will blow some part of that supply up. On the ones
I had, it'd take of the negative rail.
I put a MOV on the power rail and didn't have any more issues with power
cycling.
Interesting!
The DEC regulator modules under discussion (H744, H745, H754, etc) probably
don't have that particular problem. They are switchers, and run on 20-30VAC
input rather than directly on mains voltage. The H742 or H7420 bulk supply
which the regulator modules plug into has a large power transformer from
mains to the intermediate AC, and supports up to five regulator modules, It
also has a control module which includes one or two built-in linear
regulators (low-power compared to the plug-in switching regulators).
The PDP-11/40 has one H742 with five regulator modules. The PDP-11/70 has
two H7420s with three or four H744 regulator modules each.
Some of the regulator modules are rated for up to 150W output. The most
common, the H744, is rated for 125W (5V 25A). However, DEC designed
somewhat conservatively and didn't normally operate the regulators near the
maximum rated current. I don't think the H742 or H7420 can handle much more
than 500W total, hence the 11/70 needing two of them.
9:47 p.m.
The H744 was 25 amp, but then they came out with the H7440 28amp? And the
H7441 at 32 amp.
A lot of units were upgraded in the field.
Paul
On Mon, Sep 17, 2018 at 5:49 PM, Eric Smith via cctalk <
cctalk at classiccmp.org> wrote:
On Mon, Sep 17, 2018 at 4:17 PM, dwight via cctalk
<cctalk at classiccmp.org>
wrote:
I had a problem with brick power supplies a
number of years back. I found
an issue that caused them to fail. I had about ten of them on the same
power switch. You'd think this would not be an issue but it is.
You see it works like this, each one had a transformer in it. When you
disconnect the power, with a switch, each of the transformers often has
energy left in the cores. Normally for just one supply, this isn't an
issue. When you have a bunch of these, only one supply absorbs all of the
energy. When it does, it will blow some part of that supply up. On the
ones
I had, it'd take of the negative rail.
I put a MOV on the power rail and didn't have any more issues with power
cycling.
Interesting!
The DEC regulator modules under discussion (H744, H745, H754, etc) probably
don't have that particular problem. They are switchers, and run on 20-30VAC
input rather than directly on mains voltage. The H742 or H7420 bulk supply
which the regulator modules plug into has a large power transformer from
mains to the intermediate AC, and supports up to five regulator modules, It
also has a control module which includes one or two built-in linear
regulators (low-power compared to the plug-in switching regulators).
The PDP-11/40 has one H742 with five regulator modules. The PDP-11/70 has
two H7420s with three or four H744 regulator modules each.
Some of the regulator modules are rated for up to 150W output. The most
common, the H744, is rated for 125W (5V 25A). However, DEC designed
somewhat conservatively and didn't normally operate the regulators near the
maximum rated current. I don't think the H742 or H7420 can handle much more
than 500W total, hence the 11/70 needing two of them.
2287
days inactive
2288
days old
6 comments
6 participants
participants (6)
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billdegnan＠gmail.com -
dkelvey＠hotmail.com -
jnc＠mercury.lcs.mit.edu -
p.gebhardt＠ymail.com -
spacewar＠gmail.com -
useddec＠gmail.com