Super Rocket ammeter

[Gonemad]

Is there a difference between an ammeter from a Dynamo / Magneto 6V set up and a bike with an alternator?
I ask because the ammeter that came out of the 1960 Super Rocket headlight shell may or may not be original but needs to be replaced as it is both mechanically, and therefore electrically, finished.
I would like to replace it with the right item and the bike is, of course, a Dynamo / Magneto 6V set up.
The hole in the headlight shell is 41mm dia (1-5/8”), as is the fairly tight fitting case of the ammeter, while the bezel of the ammeter  is 46mm dia (1-13/16”)
The face on the ammeter reads, from the top down, AMPS, - + (on the scale) & LUCAS, MADE IN ENGLAND but the case is made of a cheap clear plastic which I must admit does allow good viewing of the loose and burnt out internal parts.
I have seen some on the internet with a similar face, but reading -8 to +8, but with what looks like a metal case.

Best regards to all.

Angus

[trevinoz]

Angus,
               Generally speaking, dynamo bikes used an 8 amp ammeter and alternator 12 amp.
The original ammeters were 8 amp but there were no numerals on the face, only + & -.
Not sure when the numerals first appeared.
The Lucas meter is as you described, held in place with 4 bend over tabs which broke off when the meter was removed.
Some of the metal case meters are held in with a sqare "U" bracket and are a tight fit, usually some filing of the hole is needed. Indian made but seem to be OK.
Avoid at all costs the plastic case meters held in with the "U" bracket as they tend to split around the body when the bracket is tightened.
Cheap and nasty, branded "Made In England".
I prefer the Lucas replicas which are being made.

  Trev.

[Gonemad]

Thanks Trev

Now I understand why some ammeters are 8 and some 12.

This morning I obtained one of the Indian replica ammeters.  That is marked -8 and +8 and is held in place by the little tabs on the bezel that have to be bent out. Hopefully that will be a one time operation during my lifetime.
It looks quite well made and even has the name LUCAS on the face, which my supplier indicated was no longer the case as the Lucas company had got a bit upset with the Indian manufacturer for some reason...
My supplier is a man who restores Rocket Gold Stars for a living, to a fantastic standard, and I am pretty confident that he would not use rubbish.
So, your preference for the "Lucas replicas that are being made" seems to be well placed.  Thanks for the input mate.

Angus

[Gonemad]

Just a quick follow up. 
I obtained one of the Indian replica ammeters today from my 'local' supplier. It has the word LUCAS on it and the scale is from -8 / +8, just as you mentioned Trev.
Just for once with this bike, something went right and worked first time. The ammeter slid perfectly into position and now reflects the current drawn as the headlamp is switched from side to main beam.  Very satisfying.
Thanks Trev.