V4BH Bass Amplifier
Changing the Tubes
The performance characteristics of tubes are degraded in direct proportion to how often and under what conditions the amplifier is used. Power tubes should be checked at least once a year - more frequently if you use the amplifier nearly every day. When power tubes wear out, the amplifier will begin to grow weak, lack punch, fade up and down, or lose highs and lows. Power tubes work together in a push/pull configuration and should all be replaced at the same time with matched or balanced tubes. Your dealer can recommend the best replacement tubes for your amplifier.
Preamp tubes typically last longer than power tubes. When a preamp tube wears out, the amplifier may squeal, get noisy, lose gain and sensitivity, or just quit working. A service center can determine which tube(s) may need replacing.
To gain access to the power tubes in the V4BH, the rear panel must be removed. Tube replacement should only be performed by a qualified service person.
•Turn the amp off, unplug it and let it cool for at least 5 minutes.
•Remove the screws which hold the panel to the rear of the cabinet.
•Set the panel aside.
•Gently pull the tube retainer away from the base of the tube.
•Grasp the tube at its top and gently work it out of its socket by rocking it slightly back and forth as you pull on it.
•When inserting new output tubes, align the tab in the tube’s plastic base with the slot in the socket and press the tube gently but firmly into place by pushing down on its top. (Preamp tubes have a “missing pin” which cor- respondes with the “missing hole” in the socket – line up the missing pin and hole before pressing the tube into its socket.)
•Make sure that each tube retainer firmly grips the base ot the tube.
•Replace the rear panel and tighten its screws.
•Power up the amplifier and let it sit for at least 20 minutes. Bias the amplifier per the schematic (qualified tech- nicians only!).
Troubleshooting
In the event that your V4BH should stop working properly, or just stop working, take a few minutes to troubleshoot it before you call for service. You can save yourself time and money doing it yourself, and often the problem is something quite simple. Please refer to the Troubleshoointg Diagram below for guidelines. Symptoms of tube failure are defined above.
Troubleshooting Diagram:
NO SOUND |
|
| LEDs LIGHT |
|
|
|
|
| LEDs DON'T LIGHT |
|
| |||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |||
| Check amp controls, check |
|
|
|
|
| Check AC outlet |
|
|
| |||||||
| for signal from bass |
|
|
|
|
|
|
|
|
|
|
| |||||
|
|
|
|
|
|
|
|
|
|
| |||||||
|
|
|
|
|
|
|
|
|
| OUTLET OK |
| NO POWER |
| ||||
| NO SOUND |
|
| SOUND OK |
|
|
|
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
|
|
|
|
|
|
| ||||
|
|
|
|
|
|
|
|
| Check power cord, |
| Check house fusebox | ||||||
|
|
|
|
|
|
|
| ||||||||||
Listen for hum |
|
|
|
| fuse, power switch |
| or circuit breaker | ||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| POOR SOUND |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Check bass, cables |
|
|
|
| ||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| POOR SOUND |
|
|
|
| SOUND OK |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Check speaker(s) |
|
|
|
|
| ||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |||
| SPEAKER(S) OK, |
|
| SPEAKER(S) |
| |||
| POOR SOUND |
|
| DEFECTIVE |
| |||
NO HUM
Check speaker
Speaker OK
SOUND OK 
HUM
Unplug bass, touch tip of cable
NO CHANGE
Replace cable
OK
Replace speaker(s)
POOR SOUND 
SOUND OK 
NO CHANGE
SEE BELOW |
SEE BELOW |
If the problem isn’t covered above, or if the steps lead you here, then contact your Ampeg dealer for service information. Also, you |
|
should refer your amp to an authorized service center for servicing if it gets dropped, has liquid spilled into it, or sustains damage to | 7 |
its power cord. |
