THD UNIVALVE INSTRUCTION MANUAL
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7. Light Bulb ON/OFF Switch:
The light bulb is part of the noise reduction system of
the amplifier. When the light bulb is turned on, the noise reduction circuit is enabled.
When turned off, the noise reduction circuit is disabled. The light bulb is powered by the
signal coming from your guitar. Thus when you stop playing, the light bulb will stop
glowing. If the light bulb does not glow even when it is switched on and you are playing,
the bulb may need to be replaced. The amplifier will still function, but the noise reduction
system cannot work if the light bulb is blown. Simply unscrew the lens and replace with
a #1816 bulb only. These bulbs are available through any THD dealer or directly from
THD. They can also be found at most electronic supply houses.
8. HOT PLATE Attenuator Control:
The UniValve does not have a master volume
control typical of many guitar amplifiers. Instead, the UniValve is a non-master volume
amp with built-in attenuation. The advantage to this is that you can achieve true power
tube saturation, and then utilize the built-in THD Hot Plate power attenuator to have full
output distortion at any volume level. The Attenuator control determines the amount of
attenuation applied. Turn the control all the way clock-wise and you will be attenuating
by about 3-4 dB. As you turn the control counter clockwise, the volume drops smoothly
down to almost no sound. This control is only activated when the Full Power /
Attenuator switch is set to Attenuator.
9. FULL POWER/ATTENUATOR Switch:
When set to Full Power, the Hot Plate is
completely removed from the circuit for Full Power playing into a speaker. When set to
Attenuator, the Hot Plate is placed in the signal path after the power section and the Hot
Plate Attenuator Control above is activated. The
Standby
switch should be in the standby
position when switching between the Full Power and Attenuator settings.
10. HI V/LO V Switch:
This switch determines the plate voltage of the power tube. At
the Hi V setting, depending on which power tube you use, approximately 450 to 470
volts are applied to the plates (a tube that draws more current will have a lower plate
voltage). The amp has twice as much power at this setting than it does at the Lo V setting
and results in a sound that is punchier, more aggressive and more “in your face.” At the
Lo V setting, depending on which power tube you use, approximately 300 to 320 volts
are applied to the plates. This setting will give you a sweet, warm and smoother sound
with a slower attack. To insure maximum tube life, the standby switch should be in the
standby position when switching between the Hi V and LowV settings.
11. Standby Switch:
Standby mode keeps the power tubes powered and the amplifier
itself off. Always power up in Standby mode and allow the tubes to heat up for at least
two minutes before switching to Play. The amp should also be placed in Standby before
it is turned off to cool the tubes more gradually and to reduce the possibility of internal
arcing.
12. Power On/Off:
The Power switch turns the amplifier on or off.