IG-18 mods

[Ron]

Hi, all,

Wile I haven't done any of the mods, I thought IG-18 and
IG-5218 audio generator owners may be interested in two
additional points.

First, I have measured a comparatively recent IG-5218 for
distortion and found it around 0.04% on all ranges and at
various levels. This is right at the limit of my IM-12
measurement capability.

This would indicate to me that an IG-18, 'upgraded' to
IG-5218 schematic, should perform just as well. Note that
this upgrade involves just a few components replacements,
no rework of the PCB required. If I were to mod an IG-18,
this is what I would do before attempting anything else.

Second, I did look at the IG-5218 meter linearity. While
admittedly not linear, meter indication was reasonably good.
My conclusion was that the mod (diode and resistor across
meter) was hardly worthwhile, I do not rely on the meter,
anyway. If, however, anyone decides to do it, note that the
mod schematic is wrong: the diode polarity should be reversed
(cathode to positive meter terminal). See schematic of the
AA-1, IM-22 or IM-48.

-- Ron

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