Looking for two DEC H445 power bricks for PDP 11/40 project

[dwight]

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
>>
>