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previous: Bjorn In the BF DR it’s (AB763) very few ... -- 12/5/1999 7:29 PM

Re: What does these resistors do (DR/SR)?

12/6/1999 4:02 AM
Jim S.	Re: What does these resistors do (DR/SR)? 1. The main reason for the different resistor values is that the DR's 6V6GT output tubes require a lower negative bias voltage than the SR's 6L6GC output tubes. The smaller (10K) resistor in the DR allows the bias adjust pot to select a negative voltage from a range that is closer to ground potential. 2. That 47R/100R resistor forms a voltage divider along with the 820R feedback resistor that is connected between it and the speaker jacks. The signal that is present at the junction of these two resistors is injected, 180 degrees out o phase with respect to the input signal, back into the driver/phase inverter tube. The reason for the different values is that the DR has an 8 ohm speaker impedance while the SR has 2 ohms. For any given wattage level, the DR will generate a signal with twice as much voltage (but half the current) as the SR at the speaker output jack. The DR's smaller resistor (47R) compensates for this, so the net negative feedback amount is the same.

12/6/1999 4:02 AM

Jim S.

Re: What does these resistors do (DR/SR)?

1. The main reason for the different resistor values is that the DR's 6V6GT output tubes require a lower negative bias voltage than the SR's 6L6GC output tubes. The smaller (10K) resistor in the DR allows the bias adjust pot to select a negative voltage from a range that is closer to ground potential.

2. That 47R/100R resistor forms a voltage divider along with the 820R feedback resistor that is connected between it and the speaker jacks. The signal that is present at the junction of these two resistors is injected, 180 degrees out o phase with respect to the input signal, back into the driver/phase inverter tube. The reason for the different values is that the DR has an 8 ohm speaker impedance while the SR has 2 ohms. For any given wattage level, the DR will generate a signal with twice as much voltage (but half the current) as the SR at the speaker output jack. The DR's smaller resistor (47R) compensates for this, so the net negative feedback amount is the same.

Replies:

Bjorn Thanks for that Jim, very clear and... -- 12/6/1999 4:15 PM