25 Nov
2014
25 Nov
'14
12:18 p.m.
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.
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.