PS503A
The Tektronix PS503A is a triple power supply plug-in for the TM500 system.
It has floating outputs variable 0 to −20 V and 0 to +20 V at 1 A, as well as a fixed, ground referenced +5 V output that can source 1 A. The variable supplies can be adjusted independently or can track one another.
The PS503A replaced the earlier PS503 in 1976, adding the capability to deliver ±20 V at 1 A when used in TM500 high-power compartments.
Key Specifications
| — ±20 V section — | |
| Output voltage | 0 to +20 V and 0 to −20 V, floating |
| Current limit | <100 mA to >1 A variable (0.4 A if used in low power compartment) |
| Ripple and noise | ≤3 mVp-p at 1 A load (on either rail) |
| Load regulation | ≤3 mV with 1 A / 1 mV with 400 mA load change, ≤20 μs to recover within 20 mV after a 400 mA change |
| Line regulation | ≤5 mV for ±10% line change |
| Tracking error | ≤50 mV |
| — +5 V section — | |
| Output voltage | 5 V ±5%, ground referenced |
| Current limit | 1 A fixed |
| Ripple and noise | ≤5 mVp-p at 1 A load |
| Load regulation | ≤100 mV with 1 A change |
| Line regulation | ≤50 mV for ±10% line change |
Links
- Tektronix PS503A Power Supply Restoration by NFM @ YouTube
- Tektronix PS503A Power Supply: Part 1 (cleanup) / Part 2 (repair) by IMSAI Guy @ YouTube
Documents referencing PS503A
Prices
| Year | Catalog price | In 2026 dollars |
|---|---|---|
| 1975 | $225 | ~$1,400 |
| 1976 | $275 | ~$1,600 |
| 1980 | $420 | ~$1,700 |
| 1984 | $620 | ~$1,900 |
| 1990 | $795 | ~$2,000 |
| 1994 | $995 | ~$2,200 |
Rear Interface
- Key: Power Supply (19–20)
- +20 V output (22A)
- −20 V output (22B)
- ±20 V common (24A, 24B)
(connections below require various jumper changes in the PS503 as described in the manual)
- Remote resistor or voltage programming (via 25A, 25B) or
- Remote sensing (+ Sense 23A, − Sense 23B)
Internals
The PS503A differs from the PS503 in a number of places.
Most obvious is the addition of switch S95 in the rear that enables 1 A output on the variable supplies if the PS503A is inserted into a high-power compartment.
Through the rear interface, the PS503A supports remote sensing as well as remote voltage programming by an external voltage or resistance. To implement this feature, the 503A has an extra pair of 741s (U35, U135) to buffer the reference voltage, in addition to the four 741 opamps for voltage and current regulation that are common to the PS503 and PS503A.
The Output On switch disables the ±20 V outputs electronically in the PS503A by grounding the reference buffer input. In the PS503, it physically switches the 25 VAC inputs ahead of the rectifiers and filter capacitors. The resulting inrush current spikes cause extra wear on the switch contacts.
In the PS503A, the opamps are running off unregulated supplies which can get close to or even exceed the 741 power supply specs, causing reliability issues. The PS503A adds simple 6.2 V / 27 V pre-regulators. (There is an inconsistency in the schematics in that the opamps are shown connected to +5 V or –5 V, but this refers to the ±6.2 V supplies – presumably, because before S/N B022065, zeners VR17 and VR117 were 5.1 V parts.)
The main filter capacitors were uprated for the PS503A. Later models of the PS503 have 3000 μF/50 V parts whereas the 503A has 4500 μF/40 V.
The PS503A adds output overvoltage crowbar circuits that will trip at about 26 V (fixed). The Zero Volts and Load Compensation trims found in the PS503 were removed, and 20 V full-scale trims added.
In the PS503, an LM709K regulator (TO3 case) on a separate internal heatsink provides the +5 V output. The PS503A uses a TO-220 packaged LM340T-5 mounted to the case.
Pictures
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PS503A Front Panel
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PS503A Left Internal
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PS503A Right Internal
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Switch S95 in rear of PS503A (detects high power compartment)
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PS503A Front Panel
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PS503A Left Internal
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PS503A Right Internal
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PS503A Side
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PS503A Rear connector
