[Heathkit] Re: Heathkit IM-4180 FM deviation meter

[Miles B. Anderson, K2CBY]

Whoa!

It is one heck of a lot easier to take the scale off the defective meter and
attach it to a good meter than to try to rebuild the defective meter with a
new movement.

Almost all meters are designed to deflect through a 90-degree arc, so the
scales are electrically swappable. It's just a question of making sure that
the center of the arc passes through the pivot point of the meter movement.
Beyond that, all you have to do is match up the locations of the attachment
screws.

You don't need a 200 uA meter. It probably operates as a voltmeter (measures
current through a series resistor), so you can use a meter more sensitive
than 200 uA (say 50 or 100 uA) and just increase the series resistance to
compensate.

If it is a low impedance solid state circuit you can even go the other way
and use a 500 uA movement and lower the series resistance, but that's a
little more dodgy because it may load the circuit excessively.

Performing surgery on the replacement meter movement is a recipe for
disaster unless you have a very steady hand, a sharp eye and good tools.

If the meter rests on its back, face-up, shortening the pointer isn't going
to affect accuracy. But if the meter is upright not only is the accuracy
going to be off, but it won't zero properly unless the little counterbalance
weights are appropriately tweaked. This can be done with a lot of luck in a
high quality meter movement that's meant to allow adjustment, but it is next
to impossible with a cheap movement.

Miles Anderson, K2CBY
16 the Round Pond Lane
Sag Harbor, NY 11963
k2cby at optonline.net