All tube operating points below are by no means definitive good sound recipe for your particulate tube project. Lowest THD point is not necessary best sounding one and there is always some variance even in a NOS tube batch from the same manufacturer!  Below information is only useful as a general starting point and is ment to get you in a ballpark when no measurement equipment is available.

Lowest THD operating point spectrum

30mA, -5V BIAS

Other operating points

8mA, -8VBIAS

Traced plate curves


Nobody needs intro to this tube. One of the most widely used output pentodes out there. Very linear when triode connected but has elevated higher harmonic content. Probably that’s why it’s not everyones cup of tea in this mode. Available for sale.

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