Agree that analogue AVOs are absolutely great Rex, but as per my tests yesterday, I saw 'rock solid' on a decent digi-meter when regulating. Little bit spiky on the way up from base voltage, but pretty linear for all that and none of that 22v spikey thing. Good on alternators as well, and also very steady measuring low tension voltages being generated on magnetos, which is something I measure now and then.
A cheapo £5 meter I use for simple fault-finding / continuity testing and carry in the toolboxes is comparatively hopeless, but it is still 'indicative'.
What Musky needs to do here is 'Trust the Ammeter' though - the thing seems to be running unregulated or poorly regulated, which will be for one of the two reasons under discussion, ie wiring fault at dynamo or failure of field driver in the DVR2.
Best to start at the source with these things - which means dynamo checks first now that the battery itself has been ruled out. A wiring fault between D and F would cause the same trouble regardless of the config of the dynamo and a fine-wound dyn would probably have melted if it had been allowed to produce the sorts of charge rates seen by Musky.
I don't really agree about not using nominal 6v dyns at 12, but fully accept there are 2 schools of thought. (Three if you include Altons.) I must have done over 100,000-odd miles on standard E3Ls over the past 20 years on my A and my AMC twins. Yup, there is the physics in there, natch, but it's not just Ohm's law at work, what with back emfs and all that good stuff having a bearing.
Low resistance fields get loaded running at 12, but the standard armatures are tough and support high continuous loads well . Of course, there's the high speed cut-in downside which is a big part of the raison d'être for the finer windings, but that downside is OK for country boys who don't ride round town much in the dark. I've had to replace an armature or two, some brushes and bearings and oil seals, plus one entire monkey-metal brush-end housing that snapped, but never (yet, touch wood) had a field winding die. Horses for courses I reckon, and whatever one is comfortable with.