H-555 555dectapeDrive Dec64

This document describes the Digital Equipment Corporation (DEC) DECtape Dual Transport Model 555, a 1965-era system designed for digital information storage and retrieval.

Key Features:

• It comprises two logically independent tape transports, each handling 3-1/2 inch reels of 3/4 inch Mylar tape, capable of storing approximately 3 million bits per reel.
• Data is recorded bidirectionally using the Manchester system (phase recording) on a 10-track head assembly, configured as five redundant pairs (timing, mark, and three information tracks) for reliability.
• It features a simple direct-drive system without capstans, pinch rollers, or tensioning mechanisms, utilizing specially designed air-cushion guides.
• The effective information transfer rate is approximately 90,000 bits per second, with a tape speed of 90 ±14 inches per second.
• Motion control is managed by a relay network.

Operation:

• The unit supports both automatic operation (controlled by external ground-level commands for forward, reverse, go, and stop) and manual operation via front-panel switches.
• Proper selection and command timing are crucial for automatic control due to the relay response times (max 17ms).
• Front panel controls include switches for operation mode (OFF, WRITE LOCK, WRITE), manual direction (REV-AUTO-FWD), drive selection, and an indicator lamp warning when mark/timing track writers are enabled.
• Tape loading is performed by pressing reels onto hubs and manually attaching the tape.

Maintenance:

• Adjustments primarily involve "STOP" time settings on the rear chassis to fine-tune the braking characteristics for full-speed or partial-speed stops.
• Routine cleaning of tape heads and guides with Freon 5 solvent is recommended, along with checking connector pins for straightness.