Precautions:; High Voltage - Decware ZKIT-1 Instructions Manual

PRECAUTIONS:

If you build this amp on a piece of wood make sure you strain relief the power cord by
connecting it to the wood in some fashion. Do not rely on the transformer itself to hold the
weight and constant tugging of a power cord.
The output transformers as part of their design have very fragile lead terminations. This means
bending the wire excessively, or putting anything other than tiny amounts of pulling forces on it
will result in the lead wire pulling completely out of the transformer at which point you will not
be too pleased. To reduce or prevent this from happening it is a good idea to place several drops
of super glue at the spot where each lead enters the transformers before you build your amp.
HIGH VOLTAGE — While it should be obvious, high voltage can kill. Never power up your
amplifier without a fuse and never use anything larger than the recommended value. In this case
the value is 3 amps for 120 volt operation and 1.6 amps for 240 volt operation. Also remember
that capacitors store electricity. When you power up the amp the large electrolytic caps will have
470 volts DC on them until the tube heaters warm up the output tubes enough to draw current.
This usually takes about 20 seconds or so. With the amplifier warmed up and the output tubes
draw- ing current the voltage will drop to around 400 volts. Turning the amplifier off at this point
will create a situation where the output tubes still conduct for several seconds after the power is
shut off allowing them to drain the capacitors. This is a good thing. On the flip side if you power
the amp on and then right back off the caps will be fully charged and stay that way possibly for
weeks.
The proper way to discharge caps it to use a resistor around 100 ohms and connect it between
the cap positive and ground. This allows the voltage to drain quickly without damage to the
capacitor. Shorting the cap to ground should never be done.
If you build this amplifier on a piece of wood, DO NOT operate this amplifier in a residence where
children or pets or other people can come in contact with the exposed high voltages! If you plan
to ignore this warning please get an aluminum chassis from Hammond and punch the 3 tube
socket holes on the top of the chassis followed by all the stand-off holes on the circuit board.
That way you can safely mount the circuit board inside the chassis with only the tubes sticking
out. If you choose a chassis with a 2 inch thickness you will have the option of mounting the
output transformers inside the chassis.