Heritage
The Bias 1 control adjusts the three left (front left, rear left and rear center) power tubes. The Bias 2 control adjusts the three right (front right, rear right, and front center) power tubes. By observing the LEDs as the Bias controls are slowly rotated clockwise, a number of tube problems may be diagnosed by the user as seen in the table below.
Condition | Problem | Solution |
Green comes on, then red | No problem | The longer the green LED is on before the red LED |
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| comes on, the better matched the tubes are. |
Red comes on, then green | Tubes not properly matched | Set slightly before green comes on, obtain matched |
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| tubes when possible. |
Red comes on, no green | One or more tubes are | Check to make sure tubes are all seated properly; if so, |
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| find and replace bad tube(s). |
None on | Possibly no high voltage or bad Bias | Have unit checked by a service technician. |
| Control or bad tube(s) |
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Both on all the time | Possible bad Bias Control or bad tubes | Have unit checked by a service technician. |
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If the tubes are bad enough to cause damage to the unit, the Fault Indicator (#11, Front Panel) will signal and the unit will shut down.
Block Diagram
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| BAL |
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| PWR AMP | SLAVE |
| OUT |
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| INPUT | OUT |
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| IMPEDANCE |
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| 4 OHMS |
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| POWER |
| 2 OHMS |
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| AMP |
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| 1/4" JACK |
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0dB INPUT |
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| PREAMP |
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| OUT |
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| BIAS |
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| BUFFER | ADJUST | 1/4" JACK | SPEAKER | ||
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| GAIN | MASTER |
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| OUTS |
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BASS TREBLE | MID | POWER AMP |
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| PROTECTION |
| 1+ |
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| ULTRA |
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| SPEAKON® |
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| 1- 2- |
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| HI | FREQUENCY |
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| JACK |
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| ULTRA |
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| 2+ |
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| LO |
| POWER |
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STANDBY BIAS
FAULT INDICATORS
10