Tach / alternator???

[tab1324]

Working on the bikes charging system tonight and as I revved the motor to check charging voltage, the tach suddenly came alive. This was in the 5-6K range - anything less and it didn't work. I've been having trouble with the charging system and I know the tach not working is an indicator of a bad alternator. Is this related solely to the alternator or could there be other causes like the regulator. I'm still not charging the battery so it must be in that system somewhere.

Thanks,

Tom B.