Alternator field collapse?

[ZsZ]

We are on the way home from our 3 week ostsee-nordsee road trip everything went smooth for 2.5 weeks, but I had a strange hiccup today.

I was driving on the highway, around 100-110kmph (~3000rpm) when the charge idiot light came on for a sec or two, the tacho dropped to zero then jumped up to full sweep. And then everything back to normal. Did it two times, then I slowed down to 90 and came off the highway.
It was OK since and it was before.
Tempreature was warm (around 26C ambient) the compressor fridge was running, headlights were on.
Nothing obvious is visible, the belt might be a bit looser than it was when we started so I tightened it.
The voltage regulator was new when we started the trip. Febu- Hüco branded. Ran around 2500kms since.
Was the alternator overloaded and the field collapsed?
Any other ideas?
(JX two belt setup with 90A alt.)

[Atlantik90]

I think, not the tacho (speedometer) but the rev counter droppt down.

I recomend to check.
- bearings of the generator
- collector rings
- cole brushes at regulator (perhaps they are broken during mounting


And something for happyness:
I did not know that there is a "charge idiot light" in our Bulli

[ZsZ]

Yes the rev counter dropped - tacho and idiot lights are in US english which I am used to, sorry. :)
Will check the brush pack tomorrow, when the storm is over.
Thanks!
:)

[ZsZ]

Just an update:
I recently disassembled the alternator.
The problem was caused by the aluminium shim (strip from a beer can) I added before to reduce the play between the plastic bearing retainer cage and the housing.
The shim walked out and shorted the diodes. But immediately vaporized so the charge came back.
I removed the remains and reassembled for now
It will need a new bearing and a plastic retainer.