Power Designs 2005A Precision Power Source

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.

Power Designs 2005A Technical Data.pdf