Electrical: 63 Lark pulsing ammeter

[JimKB1MCV]

Car is a '63 259 cid Lark, which I installed a new alternator on about two weeks ago. The new alternator came from Fifth Avenue Antique Auto Parts (a TW advertiser) which I had no problems installing with their instruction sheet and replacing the unit which had failed. I think the old alternator was a Nissan-Denso replacement for the original Prestolite. The Fifth Avenue alternator looks like a one-wire GM type which requires a wire to the switch or + primary of the coil.
Road tested for around 50 miles, headlights on, all looked as it should, showing slight and steady positive charge.
A few days later I took the car on the Tri-Spokes Chapter SDC spring tour, fun tour, covered around maybe 200 miles with all normal till maybe 25 miles from home when the ammeter became unsteady, not showing any heavy charge-discharge sways but more of a vibration, maybe the width of the ammeter needle. Got home OK and took a look at things in the morning. I suspected a problem with the alternator, but a VOM on the battery and on the alternator output shows a full 13+ volts. (meter is a Simpson 260).
So as far as I can see the alternator putting out. The rear frame of the alternator will attract a screwdriver at fast engine idle, also indicating output.
In the interest of full disclosure the car has several added electrical accessories, a CD player and a Yaseu 2 Meter tranciever and a Drake TR4 HF tranciever, but the condition doesn't go away with the accessories disconnected.
So I'm kind of at a loss ans looking for suggestions.
Jim KB1MCV in East Waterboro, Maine
Radio shack pics on QRZ.com

[gordr]

Could it be simply that when the new alternator was first installed, the battery was partially discharged, and so the alternator regulator caused it to put out steady; and then on your tour, the battery became fully charged, and the regulator is now switching in/out at a fairly high rate to maintain it? Maybe there is no problem? Do you have an oscilloscope in your ham shack? A look at the waveform at the battery positive post might tell the tale. What about the radios, CD player? If there were something really wrong with the alternator, you might be hearing a lot more alternator "whine" than is normal.

[StudeRich]

So your New Delco/GM Type Alt. one wire, has Internal Regulation and you bi-passed the Voltage Regulator?

[41 Frank]

My '63 Lark has done that for years, charges fine after starting the car then reverts to a vibrating needle condition after the battery has been recharged. Replaced the regulator once and the condition went away but it eventually returned. Since the regulator is actually a cut out I'm thinking that it's the nature of the beast.

[garrilla]

There's some really good reading about alternators on older cars on this site: http://www.madelectrical.com/electrical-tech.shtml
He gives great detail why 1 wire alternators don't work well for cars. Very worthwhile reading about how our cars electrical systems, especially using relays for headlights and other high amp drawing accessories.

[JimKB1MCV]

Thanks all for the comments and suggestions.
Today the operation is flawless, alternator output steady. I will put my old low-rez scope on the battery just for the fun of it. The original alternator/regulator was replaced by a previous owner and is long gone. This is my second season with the Lark and I'm liking it.
JimKB1MCV