Classic/Antique Car Repair: alternator diodes, alternator problems, sweating bullets

Question
I have a 64 Rambler (my first car!).  The other night I noticed the "GEN" light on, indicating alternator problems.  After 5 miles of sweating bullets, it just went out, and the AMPS meters switched from discharging ~5 amps to charging ~15 amps for awhile until it settled down to Situation: Normal.  I'm thinking a diode may be bad.  Is there a simple way to test?  If I replace one, should I replace all?  (I'm an electronics teacher, so can probably do that myself).

Thanks for your advice!
Bruce

Answer
Most likely the voltage regulator contacts are dirty, and after some jiggling around they finally made contact and supplied the correct input to the generator to get it to start charging again.  I think you should prepare to check out the regulator by carrying a VOM with you, so you can check the next time it happens to see if the output from the regulator is correct when the generator/alternator is failing to charge.  I'm betting you'll find the regulator is at fault, not the charging device.

I'm not certain whether your 64 has a generator or an alternator (it was a transition year for Rambler), but in either case, you have no evidence that there is a problem there.    If it has an alternator, an intermittent problem like that would more likely be a dirty or worn slip ring or contact brush.  If a diode had failed, it would only reduce the maximum charging current, not totally disable
the alternator.

Generators also have contact brushes, of course, and they can also fail, but that's extremely rare.  

Intermittent problems are almost always in the controlling devices, not the main items.

Dick