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ms660 · 12th Apr 2019, 6:53 pm

Unless there's another path from HT to anode, that looks to have the same symptoms that the osc valve had, low emission, low emission would mean higher anode voltage and possibly lower grid voltage, the bias voltage in that circuit is due to grid current, the grid current is very small, hence the high value grid resistor, often some receivers will have a higher value resistor fitted when grid current bias is used, typically 10 meg ohms or sometimes greater, measuring the grid voltage with a meter will reduce the actual operating bias voltage at the grid to an extent depending on the meter's resistance and the value of the grid resistor.

Lawrence.

12th Apr 2019, 6:53 pm	#85
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Ferguson 382U Firefly not playing ball Unless there's another path from HT to anode, that looks to have the same symptoms that the osc valve had, low emission, low emission would mean higher anode voltage and possibly lower grid voltage, the bias voltage in that circuit is due to grid current, the grid current is very small, hence the high value grid resistor, often some receivers will have a higher value resistor fitted when grid current bias is used, typically 10 meg ohms or sometimes greater, measuring the grid voltage with a meter will reduce the actual operating bias voltage at the grid to an extent depending on the meter's resistance and the value of the grid resistor. Lawrence.