Quote:
Originally Posted by Station X
Trouble is, short of inserting a meter in the screen grid lead, there's no way of measuring screen current.
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In theory the expected screen current can be deduced from the voltages and resistor values given in the Trader sheet, trouble is it's a bit pointless because the values given don't tally up with the current expected....unless I've made a mistake....
...Switched to AM, HT side of R30 (5.6k) is approx. 158 volts (mixers anode = 158 volts) bottom side of R30 = 112 volts (output valve screen voltage) so current through R30 = 8.2mA.
But, V2 anode voltage = 80 volts, therefore voltage dropped across R7 = 112v - 80v = 32 volts therefore the current flowing through R7 (2.2k) = 14.5mA, by the same method the current flowing through R8 = 4mA, through R9 = 4.2mA and through R26 = 0.3mA giving a total of 23mA, that and the 8.2mA that was initially arrived at don't compute...?
Anyone care to confirm?
EDIT: Out of interest do the Trader sheet voltages tally up with the voltages in the manufactures manual? (I've only got a copy of the Trader sheet)
Lawrence.