Bringing a Power Designs Inc. 6050D Universal DC Source back to life.
The Power Designs Inc. 6050D is the D variant and 5th in the series of 6050 power supplies. It is a linear power supply designed to output 0 to 60 volts DC in 4 decreasing amperage ranges from 5 to 1 amps as the voltage is increased. It uses the Power Designs UNIPLY® design (Patent #3,699,352) to accomplish this.
Here is the information from the 1997 website.
What is it?
Uniply offers a wide range of voltage and current in a single output bench power supply. It provides features not available with common dissapative circuits. Because of its unique design, it’s like having a family of power supplies at your fingertips. Uniply is offered in both constant voltage and constant voltage/constant current models. Simply stated, it’s a wide range constant power source.
What does it do?
By providing higher current at low voltages and higher voltage at lower currents, Uniply allows maximum flexibility in a single power supply. No longer is it necessary to have a variety of power supplies available for different purposes. A single unit replaces a multitude of power supplies.
How does it work?
To make life easier, the power supply is divided into several distinct ranges. Each range has its own DC power source which is automatically selected according to the output voltage and current requirements. When the current attempts to exceed the maximum level for a given range, an LED lights. When the output voltage level is reduced or increased, the appropriate current range will be automatically selected. There are no manual switches used to change ranges.
The power supply was purchased on Ebay, in “for parts or not working” condition. It looked pretty rough with a missing voltage control, and power switch loose inside the case.
One of the first projects for this power supply was an extensive cleaning and inspection. After looking at the condition of the electrolytic capacitors, I decided that a full re-cap would be a wise choice. All electrolytic capacitors were replaced with Nichicon capacitors.
After replacing the missing voltage control potentiometer with a VRN 84048 series 10-turn 10 K pot, remounting the power switch, and several quick checks for shorts, it was time to power up the unit.
All internal voltages checked out good, including the 4 additive supplies for the UNIPLY® electronically controlled variable impedance section. I was able to set a voltage that was rock steady under load, but could not adjust the current control for setting the constant current mode limit. There was also a problem with the front panel display when switching to the amps display.
The 2K ohm current control potentiometer ended up having an open resistance circuit, and the replacement is a Vishay Spectrol 534 series 10-turn 2 watt unit. The display switch was a sealed unit with intermittent contacts, and was replaced with a C&K 7000 series DPDT On-On unit. The display now workes properly, but still no current control.
After many hours of troubleshooting, the problem with the current control ended up being a faulty transistor Q11, a NPN 2N2205A in a TO-18 Case. I did end up adding some slip-on heatsinks for some of the warmer transistors.
The front panel and outer case cleaned up surprisingly well using several different cleaners. I used N‑Heptane for removing sticker residue from the anodized aluminum panel and acrylic display, and Novus 3, 2, and 1 for removing the scratches and haze from the display, LED, and AC indicator.
Original specifications for this power supply were:
0.005% voltage regulation
0.02% current regulation
1 mv P‑P voltage ripple-noise
5 ma P‑P current ripple-noise
Under full load at the upper voltage in each of the 4 ranges, voltage regulation was better than 0.002% and voltage ripple-noise was less than 0.25 mv P‑P.
The PD6050D is currently my favorite linear that I own, but I am currently working on restoring it’s bigger brother, the Power Designs 6150. It is a massive unit capable of 15 amps output on it’s lower range. I am searching for a PD6150 schematic if anyone has one available.
FOUND — See the PD6150 project post