Vectronics VEC-1680K - Manual (Page 18)

VEC-1680K Owner’s Manual Vacuum Tube Preamp
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Filament Pins
If the filament is okay, check the power adapter for 12 VAC output (this may be
significantly higher than 12 volts AC with no load attached).
Important Warning: Never remove the bottom cover of your preamp and
work inside with AC Power turned on--or with the AC adapter plugged into
110-VAC mains! Also, before touching internal components, discharge the
unit's three filter capacitors.
To discharge the filter capacitors, rest a small screwdriver on the edge of the
chassis to make ground contact and touch the (+) lead of each capacitor with the
tip. This will bleed off any energy stored in the high-voltage circuit.
+
_
C6
C1
+
C2
+
If the tube's filaments heat properly, move on to a test of the foot-switch
function. If you have a standard musical instrument foot switch available, plug it
into the Foot Switch jack (these are available at most music stores). If you don't
have one, use a cliplead or short length of hook-up wire attached to a ¼” phone
plug (see following diagram).
When the foot switch is closed, it shorts the plug's center terminal to ground--
energizing the by-pass relay. This routes audio signals through the preamp's
circuitry. When the foot switch is open, the Input and Output jacks are
connected together and signals bypass the preamp. This test will confirm that
the relay is activated when the foot switch is closed.