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UPSIDE - DOWN ASSEMBLY
The Model 1 printed circuit board (PCB) was designed with top to bottom symmetry. This
symmetry enables building a tube amplifier with “tube audio look”, where tubes are mounted on
top of the chassis. All parts, except tube sockets, can be mounted on the bottom of the board and
soldered on the top side (top side is the one with component references in white silkscreen). That
way, the PCB can be mounted close to the top of the chassis and tube sockets can be flush with
the top, or even slightly higher, depending on your preferences. There are few things to keep in
mind though:
- Top of the PCB should be at least ¼” below the chassis, to prevent metal chassis from shorting
PCB circuits.
- PCB has a 1/8” hole underneath the sockets. Make sure to provide support to the PCB using the
holes (in addition to the five mounting holes), to prevent board flexing and possible damage to the
PCB when tubes are inserted or removed.
- You may find it convenient to use chassis mounted sockets, in which case there is no stress on
the PCB during tubes insertion/removal. From the chassis mounted socket you can “drop” wires to
the PCB. Be sure to use short insulated wires.
- If you mount headphones connector to the bottom of the board, left and right channel will swap.
To bring everything back in order, you will need to swap inputs. Then your speakers will have left
and right channel swapped. To rectify that, you will need to connect left speaker to the right
channel and vice versa. Or, you can simply use a chassis mounted headphone jack and connect
wires to the PCB in the right order.
- When the headphones/speakers selector switch is moved to the bottom, it will reverse the
function – headphones position will turn the speakers on and vice versa. We do not think this is a
major issue but you should be aware.
- If you move volume control potentiometers to the bottom of the PCB, the minimum volume
position will become maximum. It may be cool, but it could also be annoying. The only solution to
the problem is to use chassis mounted potentiometers and bring wires to the PCB.
- If you use chassis mounted parts (input jacks, headphone connector, switch and volume control,
make sure to use short coaxial cables to minimize noise pickup and stray capacitances that may
cause amplifier to oscillate.
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