Operation Manual

16
Tube Replacement
Warning! Never use ANY power tube type other than EL34s or 6CA7s. Doing otherwise may result in damage to the
amp, unpredictable performance and electric shock.
Use or specify a matched sextet of EL34 or 6CA7 tubes.
Have the bias set by a professional. This must be done every time ANY of the power tubes are replaced. If the bias is
set wrong, the amp will not put out maximum power, the output will be more distorted, and the tubes may not last as
long.
It is perfectly normal for power tubes, like the EL34s in the VB-2, to emit a soft blue glow.
Don't pull out tubes if you don't have to. If you constantly pull the power tubes out of the amp it will wear down the
tube pins, which will cause loose connections. This will also prevent damage to the tube sockets.
It is widely accepted that antique vacuum tubes are superior, but this is not always the case. While there are fantastic
antique tubes available, they are rare and costly, and in reality, the benefits you receive are minimal.
The power tube filaments are connected in pairs as shown.
Preamp tube functions: For best performance, use only tube types specified.
(12AX7)
V1b - Input gain stage
V1a - Second gain stage
(12AX7)
V2b - Overdrive channel gain stage
V2a - Active EQ driver
(12AX7)
V3a - Power amplifier pre-driver
V3b - Cathodyne phase splitter
Pair 1 Pair 2 Pair 3