Testing has revealed that the voltmeter in my 'new' 71 Stag reads almost a
full volt high, while the spare voltmeter from eBay reads over a full volt
low. Probably the voltmeter in my other Stag reads low as well, but I
didn't test it (yet).
When I tried to calibrate the original voltmeter, I discovered that just
touching the adjustment would make radical changes in the reading ...
subsequent disassembly confirmed that there was no friction left to hold the
adjustment in place (which is very likely why it was so badly off to begin
with).
However, after reassembling [Note that I do NOT recommend dis/assembling the
unit, as some damage is inevitable], I found that a dab of clear fingernail
polish would hold the adjustment; and I was able to properly calibrate the
unit while the polish was still soft. A screwdriver in the slot is a very
unsatisfactory tool ... I wound up turning a tool to suit. But, if you
started with a flat screwdriver that will just fit into the round window,
and grind away the last 1/16" or so leaving a nub on one side (to engage the
slot), that would probably work OK.
Apply 11 volts to the gauge, and wait a minute for it to settle. Then tweak
the slot behind the "11", so the needle covers the mark. The slots move
more or less side to side, they don't really turn (which is why a plain
screwdriver works so poorly).
Then apply 15 volts, wait again for it to settle, and adjust the other slot
until the needle is right over the 15 mark. The adjustments do interact to
some extent, so repeat as necessary (but mine was close enough after one
round). I used more fingernail polish to hold each adjustment in place.
If you do disassemble the unit (again, I'm not recommending this, just
reporting what I found), the order on the posts in back is :
Thin nylon washer with a single notch, which locates over a nub in the case.
Thick phenolic washer with 4 notches, one of which locates over the same nub
in the case.
Brass terminal, with a nub located into the phenolic washer so the terminal
points upward.
Split lockwasher.
Slotted nut.
One other item : prices vary widely on clear fingernail polish at the local
supermarket. First bottle I found was $6 ... eventually I found one way
down on the bottom for only $2.50.
Randall
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