503

The Tektronix Type 503 is a monolithic oscilloscope introduced in 1960 specializing in X-Y mode but also containing a sweep circuit. It features two identical phase matched amplifiers with true differential inputs. The scope has a bandwidth specification of 450 kHz and sensitivity to 1mV per centimeter. The 503 and 504 were low priced scopes for their time but provided the same quality and precision of their higher handwidth siblings. The standard version 503 utilized a P2 phosphor CRT that provides a slightly longer trace decay time for ease of photographing the display. A large market for the scope was in electronics labs of educational institutions. The differential inputs are useful for entry level students to experiment with observing voltages not referenced to ground.

The 503 is mostly a vacuum tube design with a differential transistor stage following the differential input amplfiers. The 503 does not use post deflection acceleration, resulting in the CRT cathode operating at -3000 V.

The power supply design is unique in that, unlike other scopes where the high frequency transformer only generates the CRT operating voltages, in the 503 it generates all the operating voltages other than the two filament circuits which are supplied by the AC mains power transformer. It is basically a tube switch-mode power supply (SMPS). A 6DQ6 power pentode, V620, feeds switched primary current to transformer T620. The switching frequency of V620 is between 25kHz and 30kHz, enabling T620 to operate efficiently with much lower core mass than would be required for a transformer operating at mains frequency.

A main virtue of the 503 is its low bandwidth which enables it to operate at high sensitivities while not responding to interference from broadcast transmitter RF fields. Therefore the 503 is useful for biomedical work.

The rack mount version of the 503 is the RM503.

Tektronix 503 manual

Tektronix 503 factory calibration procedure

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  RM503 front panel 1

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  RM503 front panel 2

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  RM503 top view

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  RM503 bottom view 1

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  RM503 bottom view 2

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  RM503 rear panel

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  RM503 with rear panel input connector option

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  503

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  power supply schematic

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  Compensated input attenuator

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  503 right side