Quiana and Fandango 1.0 p 21
Location Type
V1 12AX7A
V2 12AX7A
V3 12AX7A
V4 12AX7A
V5 12AX7A
V6 6L6GC(Quiana), EL-34 (Fandango)
V7 6L6GC(Quiana), EL-34 (Fandango)
V8 (100W Models) 6L6GC(Quiana), EL-34 (Fandango)
V9 (100W Models) 6L6GC(Quiana), EL-34 (Fandango)
Here's a brief description of what each tube does:
V1 Input buffer and tone control driver for Channel 2, and also the first Preamp stage of
Channel 1.
V2 Tone control follower for Channel 2 and an additional gain stage for Channel 1.
V3 Third gain stage for Channel 2 and for Channel 1
V4 Reverb follower gain stage, and mixer for both channels
V5 Phase inverter driver tube for the power amp section
V6-V9 Power amp tubes--for best operation, all power tubes should be changed at the
same time. Use a matched pair if at all possible.
Checking for microphonic tubes
As tubes wear, some problems can come up. One of the most common symptoms is a
ringing sound. This is usually due to the tube becoming microphonic (like its name
suggests, it's picking up sound and amplifying it).
With the amp unplugged and cooled off, examine the tubes to make sure they're in tight
and straight. Never twist them! Gently grasp the tube and wiggle it into place. Because
some of the tubes are inside of metal sleeves, you will have to remove the sleeves to
check them for microphonics. Grasp the sleeve with your fingers and depress it (it's
spring-loaded) and turn to the left (counterclockwise). Now pull it off; this may require a
little wiggling action.
Preamp tube first aid
If you hear ringing (a feedback-like high-pitched sound) in your amp, it's probably
coming from a Preamp tube. Here's a procedure to find which tube is giving you trouble.
With nothing plugged into either the High Gain or Low Gain inputs, and the Master
controls turned down to 5 or below, turn the amp on.
Turn up the Volume on Channel 1, or Channel 2. Now use the tip of a pencil to gently
tap the end of each of the small tubes (V1 through V5) and listen for sustained ringing.
Turn up the Volume and Master knobs and keep tapping until you find the tube that
rings (or squeals).
(5 pages)
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