Data Sheets

[wdcw]

Gday Everybody,

Just a query about the datasheet info on the tubes.

I noticed some sheets say Idle Current etc, but on the data sheets where they just specify say Plate current 58mA for instance.
Are the Data sheets refering to Plate Idle current dc or where not specified Maximum load figures, or rms or Average with both the AC & DC components calculated.

Also the Plate dissipation figures, take 9W etc. Are these figures rms values, average values or maximum peak values.


Cheers

[DF96]

A data sheet will usually give at least two sets of figures. One set is maximum ratings, for things like cathode current, anode voltage, anode dissipation. The other set is parameters for a typical application, although these tend to be configured for the maximum possible gain so that the valve looks good.

Voltages may be peak or RMS, but they should say which. Currents will usually be quiescent (i.e. no signal). Power, such as anode dissipation, will normally be averaged over a cycle of the signal - some people call this RMS power but there is no such thing. The peak power, at one signal peak, could be up to twice the average power but it is only present for a brief time and is balanced by much lower dissipation at the opposite signal peak. You can get away with this because lumps of metal don't change temperature very quickly.

So an anode dissipation given as 9W maximum means that when no signal is present (ie. quiescent) you can't have more than 9W. When signals are present the peak dissipation can increase for part of the cycle, provided it is balanced by reduced dissipation for another part of the cycle. For a pure linear Class A stage the average anode dissipation actually goes down when signal is present.