OPERATION MANUAL MODEL : CSP3 - CLASSIC STEREO PREAMP
REV 1 MAR 2018
Installing Tubes
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There is nothing particularly special about installing the tubes other than making
sure they are the correct ones! In the case of this preamp, we ship it with (3) 6N1P
tubes which are all 9-pin tubes. It makes no difference which of the three 9-pin
sockets you put these tubes in.
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The large octal (8-pin) tube is the rectifier tube and can only fit in the larger socket
and only rotated a certain way so that the plastic dowel key in the center of the
tube socket lines up.
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Make sure tubes are OFF and COOL before you remove or install them. Contrary to
popular misinformation, you can touch the tubes without having to clean your
finger oil from the glass. Your finger oil will have no effect on the operation or the
life of the tubes.
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Tube Matching
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Matching the tubes is not required in the CSP3 preamp since the channels can be
individually adjusted; however it is nice to have the left- and right-rear 9 pin tubes
matched when possible so that you do not have to correct for channel imbalances
that might otherwise result.
The input tube at the front of the preamp actually serves both channels; meaning
the left triode section of the tube does the left channel and the right side does the
right channel. Again, while not required, it is nice to have this tube with matched
sections so the channel balance remains true without adjustment.
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Tube Substitutions
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Rectifier Tube
- Used to convert high voltage AC to high voltage DC. The factory
supplied rectifier is either a 5U4 or a variation of it, such as the 274B from Valve
Art.
The CSP3 uses a 47uf 500V capacitor in the first section of its power supply, so
many 1940s rectifiers and remakes are not compatible since they want to see less
than 10uf 500V capacitors. When buying fancy rectifier tubes always be sure they
will be compatible with 47uf 500V capacitors.
The recommended rectifier tubes for this preamp are: 5U4G, 5AR4, 5Y3GT
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