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Page 35
7.2 Parts List
QTY
Description
Designation
PCB
1
12AU7 Input Buffer PCB
Tubes
1
9 pin valve base
1
12AU7 tube
Resistors
2
470K
R1-1, R1-2
2
2K
R2-1, R2-2
2
47K
R3-1, R3-2
2
470K
R4-1, R4-2
1
8K2
R6
Capacitors
2
.22uf film
C2-1, C2-2
2
100uf 16V
C3-1,C3-2
1
33uf 350V
C1
Before we begin, let's talk for a moment about installing valve bases.
Use some masking tape to secure the valve base to the board prior to soldering.
The key is to
make sure the valve base is level
: if you have a base that is soldered in on an angle then your
tube will also lean over! Generally, you'll want to solder from the underside of the board. We
suggest that you use just a little solder to secure each pin to the board: perhaps just start with
two pins which are opposite to each other to make sure the base stays level — then you can add
more solder to the pins. In the end you can fill up the entire valve base hole.
Be very careful not
to let any solder bridge to the next pin as this will cause a short!
We recommend you then
'touch them up' from the top, then back once again to the bottom — and all should be well.
When you do the touch ups just give them a very short bit of heat and a very small bit of
additional solder.
7.3 Building the 12AU7 Input Buffer PCB
See the note on the parts list bag about the solder bridge you must make to ensure correct
filament operation – the board uses a 6.3V filament. In order to supply 6.3V to a 12AU7 you
must short pins 4 & 5 and feed the 6.3V AC to pins 4 and 5 on one side and then pin 9.
