Trinity Amps Trinity Tweed Amp, Builder'S Manual

Page: 51 / 77

Version 3.2 Page: 51
Making a Voltage Measurement
Before attempting to make a voltage measurement, think about the anticipated result.
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Is this a DC or AC voltage?
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How much voltage will be present?
•
If things are not working correctly what is the highest voltage that I might find?
A voltage is ALWAYS measured between TWO points. Is one of those points CHASSIS
GROUND? This is the most common case. If not, can you make a different measurement
such that one of the measurement points IS GROUND? If your measurements are all
referenced to CHASSIS GROUND, you can then connect the black lead (Negative or
Common) to the CHASSIS with a clip and probe the other test point with the RED (Positive)
lead.
1. Set the selector switch on the meter to the range that is higher than the maximum
anticipated voltage of the appropriate type (DC or AC). If the maximum anticipated
voltage is not known, set the meter to the highest range available.
2. Wherever possible connect the meter into the circuit when the circuit is OFF, then
power up the circuit without touching anything.
3. Read the meter. If the reading is lower than the next available lower range on the meter
you may set the meter to a lower range while the circuit is on. When doing this touch
ONLY the meter with ONE hand, and be careful to only lower the meter one range,
allow the readings to stabilize (2 or 3 seconds) before proceeding further.
Note: Accidentally setting the meter to a current or resistance range can damage the meter, and
the circuit it is connected to. If the circuit has sufficient power the meter can explode or burst
into flames. I know from experience that this will happen if you try to measure the resistance
of the wall outlet. Most modern meters are "fuse and diode protected" this is to prevent
fireworks, but will not usually save the meter from an overload of this magnitude.
Discharging the Power Supply
If you need to service the amp after having it on, you must “discharge” the power supply
capacitors. This is done by unplugging the amp, turning the power and standby to the on
position and letting it sit for 30 seconds or so. If you do not have a standby switch, you will
need to short the capacitor positive leads to ground with a 220K 2W resistor on a lead with an
insulated wire. You hear a small pop when this is done. This is just the cap discharging itself.
Always use a multimeter to check the residual B+ voltage in the large filter capacitors to make
sure it is fully discharged.