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Checking tape travel

Tape travel

Once in a while a problem comes across of which the cause is not so obvious. Like this one: while adjusting the azimuth of a Technics RS-1700 record head, the recorded test tone was unstable, varying in amplitude. After confirming nothing was wrong with the recording circuits, the quest started to find the root cause.

With a magnifying glass the tape travel showed to be unstable, meaning it was shifting across the heads. During transport the tape acted like a snake instead of a perfect straight line. A very odd phenomenon.

The most obvious reason for this could be misaligned tape heads  (tilt adjustment), but this could be almost certainly excluded as the headblock has been refurbished Summertone in the UK. Terry Summers is an expert in relapping and aligning magnetic heads and I’ve never had complaints before about his work.

The pinch roller(s) is the second most likely culprit causing tape skew thus maybe my problem as well. But the Technics pinch rollers were replaced by brand new ones. Also tape tension was adjusted according the service manual and checked with a Tentelometer…

The video shows tape travel in forward play mode along the forward erase/record head. Here the shifting tape is most severe, but it already starts at the other side of the headblock where the reverse heads are located, just after the left pinch roller (first roller in forward play mode).

The tape in the video is a new LPR35 of Recording The Masters (RTM). Finally I also tried several other tape formulas/brands and found to my surprise for some tapes the snaking was less or even not visible.

For now I can only guess the LPR35 has a more smooth oxide surface or structure and is therefore more susceptible to irregularities in the tape transport. What exactly triggers  the tape to start shifting is still not clear, so the search continues…

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