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Old 19th Oct 2004, 6:26 pm   #8
Leon_Crampin
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Default Re: Replacements for an EL33

Paul, I think you might be missing a trick in suggesting that I attach unreasonable importance to valve slope.

For an open loop configuration used in many radios, with a given (fixed) input, if you halve the valve slope, the power output goes down by a factor of 4.

Suppose an output valve has a slope of 10mA/V, and sees 1V rms input at the grid. The anode signal current (superimposed on the static anode current) will hence be 10mA rms. If the load is 5k Ohms, the signal voltage will be 50V rms and the power output consequently 500mW.

Keep everything the same, and let the slope be 5mA/V. The anode signal current becomes 5 mA rms which gives 25V rms across our load. The power output thus becomes 5 x 25 = 125mW.

500/125 = 4

As the human response to an audible energy source is logarithmic, this is a simplistic approach in terms of perceived result, but you would notice the difference.

Regards, Leon.