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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 9th May 2006, 3:05 pm   #1
Mike Phelan
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Thumbs up How an autochanger velocity trip operates

I am prompted by this, as there have been a few questions recently on the subject, and there has always been a misconception regarding their operation.

First, a bit of an overview:
We are talking about most BSR decks UA6 type mechanism and later UA12 types, and some Garrards - SP25, AT6 et al.

The trip is intended to operate either manually, or when the stylus reaches the run-out groove on the record; this moves the large cam gear by rotating it slightly; this rotation causes the gap in the teeth to move so they engage with the turntable hub gear, thus starting the trip cycle.
The cam gear has two pivoted levers - the trip pawl below and the trip lever uppermost.
There is a sliding lever that operates the trip lever by either the arm moving inwards, or by the manual reject knob.
The turntable hub has a projection to arrest the trip pawl. The trip lever rests lightly on the trip pawl and can rotate slightly.

Operation:
Deck is running, and about 5mm before the end of the record, the sliding lever pushes the trip lever, which, by gravity, pushes the trip pawl inwards so a projection on it encounters the hub projection.

Every time this happens, the stylus has moved by a groove-width, and the trip pawl moves a minute amount each time, so the hub projection pushes it back out of the way, the friction on the trip lever allows this to happen.

When the runout groove appears irrespective of where on the record it is the trip pawl is moved far enough in to be arrested by the hub projection, starting the trip cycle.

After the pickup arm has swung out near the end of the cycle, and the sliding lever moves away from near the trip lever and trip pawl, a ramp on the trip lever encounters a stop on the deck and pushes it and thus the trip pawl as well, back to their resting position.

http://static.flickr.com/53/143452546_68e5e5fe8a_m.jpg

The main problems are due to grease or oil ending up on the trip pawl and lever - they should be completely clean and dry.
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Old 9th May 2006, 4:22 pm   #2
Nickthedentist
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Default Re: How an autochanger velocity trip operates

Thanks Mike

I've owned dozens of autochangers, and thought I knew exactly how they worked. But I see I was wrong

Your explanation is a model of clarity and I have printed a copy for future reference.

Nick.
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Old 9th May 2006, 6:07 pm   #3
Chris Quinn
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Default Re: How an autochanger velocity trip operates

Excellent, although I will need to read a few more times and have a play before it really sinks in. I have a BSR on the bench so I'm off to play.

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Old 9th May 2006, 6:21 pm   #4
Nickthedentist
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Default Re: How an autochanger velocity trip operates

I always wondered why moving the arm rapidly towards the spindle seemed to cause the mechanism to engage, even though the stylus was nowhere near the label. I always imagined it was fault
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