Just got another PDP-8/S! Desktop this time!
dbradatanu
An *extremely* lucky find. I just got a PDP-8/S Desktop model.. the only one
known to exist..and the only one to run (well, in a couple of days).
The power supply is very strange. Just a transformer, full wave bridge, 6
capacitors.. No regulation or pots to adjust the voltage. The caps checked
out great - no leakage!
Check http://www.pdp8.com/8sdesktop.htm
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PDP 8s and other things...
Ron Howes
dbradatanu <dan...@internet.look.ca> wrote in article
<kuxf4.57800$Ke.5...@news21.bellglobal.com>...
> Wow!
>
> An *extremely* lucky find. I just got a PDP-8/S Desktop model.. the only
one
> known to exist..and the only one to run (well, in a couple of days).
>
> The power supply is very strange. Just a transformer, full wave bridge, 6
> capacitors.. No regulation or pots to adjust the voltage. The caps
checked
Its called a ferroresonant power supply - used a special transformer with a
saturating magnetic shunt and a resonant tank circuit. You'll note that one
of the caps is a husky AC style part, with a very high voltage rating
(maybe in the 660 Volt range). The saturating core of the transformer
produced a near constant square wave output voltage that was easy to filter
into DC. The resonant tank (the AC cap and shunt circuit of the
transformer) acted as a kind of electronic "flywheel" that gave the circuit
ride through in case of a power interruption. Very commonly used in the
early days because of their extreme simplicity, ruggedness, and regulation.
Disadvantages were the high cost, large weight of the transformer, and the
circuit was built for only one line frequency - 50 hertz required a
different AC cap and transformer winding (some designs had taps).
Ron Howes
> Check http://www.pdp8.com/8sdesktop.htm