Preamp tube locations are indicated by tube type on the rear panel of the chassis. Tube types are factory selected for superior performance, consistent tone quality and reliability. While substituting other brands may not cause damage to the amplifier this may affect amplifier performance in unpredictable ways. For best performance, replace only with factory recommended tubes. Warning! Substituting other tube types is not recommended.
Each 12AX7 has two sections/functions. Section A is shown first, Section B is second. Factory recommended tubes are listed under each location. Numbering sequence is right to left looking at back of amp starting with the row closest to front panel of amp.
V1 (shielded tube) Input Gain Stage 1 (Parallel Triodes).
12AX7A Tung-Sol
12AX7WB Sovtek
(Use in place of Tung-Sol for smoother top end and less upper mids.)
12AX7 China Selected
(Use in place of WB if more gain is required)
V2 (shielded tube) Gain Stage 2.
12AX7A/7025 China
(Gain Stage 4. Active only when MORE / LESS switch is set to MORE).
V3 (shielded tube) Gain Stage 3.
12AX7A/7025 China (Tone Control Driver).
V4 - Phase Inverter.
12AX7A/7025 China