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CONNECTING POWER:
As any other vacuum tube amplifier, Model 1 needs two voltages for proper operation: (1) Plate,
or Anode voltage, Va and (2) Heater, or filament voltage Vf. Plate voltage should be brought to the
terminal block J80 and filament voltage to J90. Picture below shows the layout detail with J80 and
J90.
Plate voltage (Va) should have nominal value of 250V (acceptable range is 200-270V). The power
source should be able to provide 80-100mA for basic configuration and 160-200mA for the full
pack. Sound is significantly affected by the power supply quality, so make sure to have sufficient
filtering.
PCL82 tubes are designed for series connection of their filaments, so they require current source
(as opposed to some other tubes that require voltage source for filament supply). Heater
specification for this tube is 0.3Amp and 16V. Rugged construction of the tube’s heater allows that
it is powered from the voltage source as well, but you can expect high current surge and bright
yellow heater in the first few seconds of operation. In theory, this reduces life of the heater, but
these tubes are very rugged and will have long life even in this less than perfect situation. Basic
version of the Model 1 amplifier has the two heaters connected in series, so the filament supply
needs to be able to provide 32V at 0.3A. Resistors R290-380 are placeholders for jumpers which
allow for different heater configurations. ECL82 tubes (which are PCL82 equivalents with 6V
heaters) can also be used, by configuring all heaters in parallel (R290 to R360 installed, R370,
380 left out). For more details refer to the description of the heater configuration jumpers, above.
Filament voltage can be DC or AC, so there are no polarity markings on J90. If the DC is used, left
pin is the system ground (see the Figure above), so the negative polarity of the filament voltage
can be connected to that pin, although doing opposite will not affect operation, as long as filament
supply is independent of plate supply.
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