The Beast, A 300 Watt Amplifier

made from a salvaged HP6129C "Digital Voltage Source"

 
The Hewlett Packard 6129C "Digital Voltage Source" is a typically 70's vintage, high quality 60Volt/5amp power supply.  What makes these units so inexpensive on the surplus market is that there are no front panel controls to set the voltage or current limits and voltage take-off is via the rear panel.   Instead, the parameters are set on the parallel port at the rear of the unit via a dedicated controller, PC or HP Switch. The unit shown below was purchased at auction on Ebay for $19.99.  Shipping was another $40! hp 6129 uncovered.jpg (186250 bytes)
As illustrated to the right, the 6129C is massive, weighing in at close to 80 pounds.  Construction is typical HP, which means rugged and excellent.  Voltage and current are displayed on front panel meters.  The drawer at the bottom allows the user to slip in DAC, Preamplifier and Controller cards. A block diagram of the HP6129C is shown below: hp 6129.jpg (190011 bytes)
The data on the parallel port sends information to a discrete 16-bit Digital to Analog Converter.  Output of the DAC ranges from 0.5mV to 8.192 V, plus a bit for "sign".  The voltages are summed and amplified through logic and analog circuitry on the slip-in cards.  The connector pinout is illustrated to the right.  The HP Pocket Programmer for the HP DVS is shown below: