Lucas Dynamo Interchangeability?

[Chris KC]

Am I correct in understanding that Lucas C35A and C35M dynamos are electrically equivalent?
That is to say, can you swap one for the other without altering anything else in the system e.g. the cut-out?

Is there any consensus that one is better than the other?

Thanks in advance.

[Dave Wortley]

Chris, I don't bother with the half charge function and have swapped C35A/C35M many times. I prefer C35M because I think the brush that slides inside the holder works better than the pivot brushes in the C35A.

[David Stepney]

The C35M Instrument has no field resistor built in (on?), but it is an easy job to fit a 1.5 to 2 ohm resistor into the half charge circuit to make it work.

[Chris KC]

Thanks both.

Dave W, yes I had the same thought about the brush mechanism. Though it doesn't seem a huge reason to reject a C35A if one is to hand.

Dave x 2, about the half-charge function, are we saying it won't work if a C35M is fitted to a car wired for a C35A, unless a resistor is added? Where precisely would it be added? Does this imply that something else (e.g. the cut out?) differed on cars with C35M fitted from new?

[JonE]

CFR2 cutout/PLC2 switch would be most cars with C35M, with potential for three different resistance levels in other cars than Austins.
CFR was the earlier one. See Hales's Austin 7 charging/ Electrics book which is uploaded on the web if you search

Didn't some C35A have the resistor pack, and some later ones not?
What have you got got by way of cutout and switch, Chris?

[Chris KC]

Thanks Jon, I have now found Harry's book which I confess I've not seen before, I think it answers all my questions.