User`s manual

Tube layout and replacement
The Sabre uses five 12AX7/ECC83 tubes and EL34. The preamp tube function is as follows,
starting at the side closest to the input jack: CH1 preamp 1/CH2 preamp 1 (12AX7/ECC83), CH1
effects recovery amp/CH2 preamp 2 (12AX7/ECC83), CH2 preamp 3/CH2 preamp 4
(12AX7/ECC83), CH2 effects recovery amp/CH2 cathode follower (12AX7/ECC83), and phase
inverter(12AX7/ECC83). The chassis top view layout is shown in the diagram above.
The preamp tubes are housed in removable "bayonet" metal shields. The shields can be
removed by pushing down on them and rotating the shield to the left, then pulling it upwards off
the tube. The tube can then be pulled out of the socket.
You may freely sub any 12xxx type tube in the preamp and phase inverter positions. It won't hurt
anything, and you may find some different tones you like. The 12AU7 is a good lower-gain tube,
as is the 5751. Other choices are 12AY7, 12AT7, or 12AZ7. In addition, different manufacturer's
tubes will sound different. Some people prefer the tone of various Ei, Sovtek, or other tubes, and
some insist on NOS tubes for a true vintage tone. The JJ/Teslas are the least microphonic, but
are a bit compressed sounding when compared to the longer-plate tubes. The Chinese 12AX7’s
are a good compromise between microphonics and a more “open-sounding”, or less compressed
tone. Feel free to experiment!
Note: vacuum tubes, especially output tubes, can get very hot in normal operation, and may
cause burns if removed before they have a chance to cool down. Be sure to wait several minutes
before replacing tubes to allow them to cool down. Do not, under any circumstances, remove or
replace the tubes with the power on, as this could cause a deadly electrical shock should the
glass break, exposing the high-voltage plate terminals. Also, be sure to pay attention to the
orientation of the tubes when putting them back in the socket. The tube pinout is keyed so it can
only be placed in the socket in one direction, and if the tube is forced in incorrectly, it can damage
the tube or the socket. The octal output tubes have a phenolic key that fits a corresponding
keyhole in the socket. If this key is broken off, it will allow incorrect placement of the tube in the
socket, which could result in damage to the amplifier. Be sure to carefully examine the tube
before replacing it.