EICO 667 TUBE
TESTER

Here is the schematic from the Eico
667 tube tester. It is very similar to the 666, except now there are
a pair of extra levers, and a few test sockets are missing. But the meat and
potatoes are identical. If you are planning to restore your 667 to peak
operating condition, here are a few pointers.

Replace the selenium diodes CR1 and CR2. I rivet in a small
terminal strip, using the mounting hole from the 'old' diodes. It is now easy
enough to install 1N4007 diodes across the terminal strip.

While you are at it, replace filter capacitors C1 and C2.
Since modern-day capacitors are much smaller than their ancestors, I replace
C1 with a 22uF/150VDC or possibly a 47uF/150VDC capacitor, while
C2 is now a 22uF/25VDC capacitor. Typically I use whatever I happen to
have on hand.

Carefully check the calibration potentiometers R7 and R18.
If you are having any difficulties calibrating your tester, change
these potentiometers! Replace them with any quality 100K linear-taper
potentiometer. I make sure I use a control with a nylon shaft, and avoid those
with split and/or splined shafts. If necessary, I also cut a notch in the top
of the shaft, to facilitate using a small screwdriver for any adjustments.
Eico used very poor quality controls here, and they are prone to
failure.

When doing the calibrating for the Line Adjust, I will set it so
'High Noon' gives me a reading of 6.3VAC with a 6L6 inserted in the socket!
This may seem obvious, but I sometimes carefully calibrate the Line
Adjust exactly as the manual describes, and I end up testing a 6L6
with barely 6VAC on the filaments. I choose a 6L6 as opposed to a 6V6 because
the filament draw is higher, and I want to be sure this procedure is done
under a decent sized load! You can measure the filament voltage while testing
say a 12AT7 or a 6SL7 after, and be sure your filament voltages are
consistent, and correct! Tweak the Line Adjust calibration as
necessary.

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