Cleanup and Calibration of a Power Designs Inc. 2005A Precision Power Source.
I managed to get very lucky on Ebay, and won this Power Designs Inc. 2005A Precision Power Source for $52.61 shipped.
The 2005A is an oven stabilized precision DC power source, designed to supply an extremely stable 0 to 20 volt, 0 to 500 milliampere output.
Two dual concentric decade dials operate four decade switches which set the output voltage in 1 millivolt increments from 0 to 10 volts. There is also a 10–20V switch that adds 10 volts to what is selected on the dials, along with a single turn 1 millivolt range potentiometer that allows adjustment of the output with a 10 microvolt resolution.
The 2005A includes a vertical meter readout that is selectable between 0–25 volts or 0–500 milliamps. Maximum current can be set by pulling out the current knob and adjusting the reading on the meter using the dial to set the current, and then pushing the knob back in.
Estimated date for this unit is 1969, making it around 49 years old in 2018.
The PD 2005A has a stability of better than 0.001% +100 microvolts per 8 hours; and better than 1 millivolt per week (at constant line, load, and ambient temperature after warm-up).
The reference amplifier oven is the primary source of this stability, along with the circuit design and selection of components.
This unit uses discrete components and no IC’s. There are no printed circuit boards (PCB’s), connections are made using turret board construction. Transistors are mounted upside-down using plastic insulators to prevent shorting to the metal cans. All wiring harnesses are hand laced using waxed lacing cord.
I did end up replacing capacitor C3, a 50 uF 150V unit with a Nichicon 100 uF 160V rated capacitor, as it was slightly below specification. All other capacitors were well within specifications with low leakage current. Amazing for a nearly 50 year old electronic device.
Most of the maintenance performed was cleaning, especially the decade switch section. I used DeoxIT D5 and DeoxIT Gold along with a micro swab to physically clean and lubricate each contact and associated resistor. A small amount of grease was also applied to the detent sections of the switches.
Other mechanical issues involved re-aligning the concentric dials which were out of position both radially and laterally, and repairing the digital dial window.
I tried touching up the white paint on the rear of the dial window, but it ended up looking like someone had touched up the paint. The paint used on my unit was a water soluble type and was easily removed, which then allowed me to use some Novus #2 plastic polish to remove some fine scratches. I opted to use some polarizing film instead of white paint for the digital dial window.
All that was left to do was a calibration using a Keithly 2015 6–1/2 digit meter. The calibration was fairly easy, involving adjusting four potentiometers and following the instructions from the manual. I only ended up adjusting R10 and R17, the Zero adjustment and Voltage adjustment potentiometers, as the others were spot on.