Rivera Knucklehead Reverb KR 100 T Troubleshooting Guide download pdf (Page 34)

Knucklehead Reverb 1.0 p 34

Here's a brief description of what each tube does:

V1 Input buffer and tone control driver for Channel 1, and also the first Preamp stage of

Channel 2 and Channel 3

V2 Tone control follower for Channel 1 and an additional gain stage for Channel 2 and

Channel 3.

V3 Third gain stage for Channel 1 and final gain stage for Channel 2

V4 Final gain stage for Channel 3 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 set of 2 (55 Version) or 4 (100 Version) if 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, Channel 2 or Channel 3. 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).

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Rivera Knucklehead Reverb KR 100 T Troubleshooting Guide Page 34