Who's rewired their house for this hobby?

Jon Elson elson at pico-systems.com
Tue Nov 25 20:42:40 CST 2014

On 11/25/2014 02:18 PM, Eric Smith wrote:
> On Mon, Nov 24, 2014 at 8:46 PM, Jon Elson <elson at pico-systems.com> wrote:
>> The KL10B had an immense 3-phase transformer, star rectifier and capacitor
>> bank,
> About 3.9F worth of capacitors, which was a heck of a lot back in the mid 1970s.
>> which produced about 12 V DC.  This was fed to a massive linear
>> regulator on a huge round heat sink.
> Actually to 13 massive linear regulators on multiple large heat sinks.
There may have been several versions.  The KL10B in a 
Decsystem 2020 we had had
one big regulator that was a ring of "christmas tree" 
segments with a fan about 10"
in diameter.  This was all 30 years ago, so my memory may 
have faded just a
little, but I'm pretty sure that was how it was done.  Quite 
insane.  DEC started
using switching regulators in all large DC supplies in the 
late 60's, and if ever
there was a machine that cried out for a switching regulator 
it sure was the
KL10!  So, the decision to use a linear regulator with a 
huge voltage drop
must have been some misguided belief that ECL was too noise 
for a switching regulator.  I have built smaller systems 
with ECL, and found
it to be quite noise-tolerant.
>> Compuserve ran a LOT of KL10B's, and designed
>> their own switching power supplies to save power and air conditioning costs.  They
>> never got DEC to pick up on that, so had to retrofit all the machines as they came
>> in.
> When the KL10 was designed, DEC was already using switching power
> supplies in some machines (e.g., PDP-11/40, /45, /55, /70). However,
> the load regulation, ripple, and noise specs weren't great, and ECL is
> sensitive to the ripple and noise. By the time Compuserve designed
> their replacement, switching power supply technology had improved
> somewhat.
Well, the KL10 was not an early CPU design.  There are ways 
to make good switching
supplies, DEC should have done the engineering.  I'm sure 
even **I** could have built
a workable switching supply.


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