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Vintage threads from the first ten years
| previous: Blues Lyne "Too bad none of that will work rig... -- 10/5/1999 5:15 AM |  |
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Re: Cathode bias questions
 10/6/1999 2:02 PM |
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Scott | Re: Cathode bias questions After reading Bruce's reply above, I took some measurements on an 2-6v6 amp of mine with adjustable fixed and cathode bias to verify that I had not missed something. Fixed Bias measurements: Plate Voltage: 335V Cathode Voltage: 335V Voltage Drop Across Tube: 335V Grid Voltage: -25.9V Tube Current Flow: 19 ma per tube Using a variac to adjust the voltage, I switched to cathode bias and measured the following: Cathode Bias Measurements Plate Voltage: 361V Cathode Voltage: 26.0V Voltage Drop Across Tube: 335V Grid Voltage: 0V Tube Current Flow: 19 ma per tube I then measured the cathode resistance value : 660 ohms Check against current 661 x .038 = 25.1V pretty close What this means is if you lower the plate voltage by the bias amount, record the fixed bias voltage reading, and then use that to calculate a cathode resistor, it will come very close. The 15W wirewound rheostat is easier, as I suggested in my first post on this issue. |
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| Bruce Scott, |