Eico Impedance Bridge

[Jack Crenshaw]

I'm in love!!  In an orgy of eBay buying, buying old tube test equipment, I ended up with
no less than three Heathkit IB-2A's.  They look very professional and impressive: Big,
lots of dials and switches. Not a single one works.  Not one.

So I saw this Eico bridge, the model 950B, and got it for under $18 bucks (I had paid up
to $36 for the Heathkits, and been involved in bids that went over $150 before I backed
out).  The Eico is a miracle of modern (well, 40-year-old) engineering.  Where the
Heathkits have four tubes, the Eico has two:  The rectifier and an eye tube.  The
Heathkits have a 1000 Hz oscillator (one is badly distorted, the others no workee) the
Eico uses a fairly stable sine-wave source: The wall.  Windings on the power transformer
supply filament voltage for the tubes, HVDC bias for capacitor testing, _AND_ the signal
driving the bridge.

It has only two "main" moving parts:  a function switch and a precision pot.  That's it.
The function switch throws the bridge into different configurations for different ... um
... functions.  Two other pots help test filter caps.

The bridge works perfectly.  Nulls are very obvious on the eye tube, easily found, and
extremely precise.  All resistors are 1%, and the readings are spot on.

I'm very impressed.  Just thought y'all would like to know.

Jack

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