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Heater Setting
There are two small recessed toggle switches on the left side of the amp. The leftmost switch
selects the heater voltage, either 6.3V or 12.6V. Set this switch to the heater voltage required
by the tubes in use. See the tube datasheet to determine this value. It is not possible to damage
12.6V tubes if you accidentally use the 6.3V setting, but it is possible to damage 6.3V tubes if
you use the 12.6V setting. The heater current is limited, but this limiting cannot protect for all
possible 6.3V tubes. PLEASE CHECK YOUR HEATER SETTING CAREFULLY BEFORE YOU TURN ON
THE AMP.
Plate Voltage Setting
The rightmost switch on the left side of the amp selects the plate voltage. Most of the tubes
that will work in the Liquid Glass® can operate at the 300V setting. This includes 6SN7s and
12AU7s and their equivalents.
However, some tubes like 6922s cannot handle the higher plate voltage. For these tubes select
the 200V setting.
Remember that in a totem pole arrangement each triode sees only half the applied plate
voltage. This means that at 300V each triode sees 150V and at 200V each triode sees 100V.
To determine which settings to use find the data sheet on the tube type you want to use.
Locate the
maximum plate voltage
in the data sheet. If this voltage is 150V or higher use the
300V setting. If this voltage is less than 150V, use the 200V setting.
Setting the plate voltage to 200V for tubes capable of 300V will not harm them, but setting
plate voltage to 300V for 200V tubes can cause internal arcing in the triodes and damage both
the tubes and the amp. Please be careful with this setting
Heater and plate voltage are the only two settings you need to make in the Liquid Glass. The
amp handles the rest.
Maximum Values
Please pay attention to these maximum values when selecting tubes:
Heater Current
– the heater circuit can handle about 1.2A of heater current. This means that
6.3V tubes can have a maximum of 1.2A heater draw, but 12.6V tubes can only have a
maximum of 600mA.
Plate Current
– the Liquid Glass HV supply can deliver a maximum of about 40mA. The HV
supply has an automatic shutdown feature that will turn off the amplifier if this maximum value
is exceeded.
