Low emissions

MrCurwen · 20th May 2011, 09:46 AM

I'm wondering what effects does low emission capability have on tubes. It's obvious that with lower emissions the maximum cathode current is reduced. What else changes? Mainly my concern is plate resistance and thus the curves.

Is there any difference with low emissions from age and wear, or low emissions on account of sub spec heater voltage?

Are curves measured in a low emission situation reliable (at least at lower cathode currents)?

DF96 · 20th May 2011, 10:34 AM

Low emission is likely to mean that current and gm go down. As mu will remain largely unchanged, the anode impedance will rise. This means that, on average, a triode circuit will survive valve ageing better than a pentode circuit - triode amplification is largely set by mu, but pentode amplification largely by gm.

20th May 2011, 09:46 AM	#1
MrCurwen diyAudio Member Join Date: Feb 2010 Location: Helsinki	Low emissions I'm wondering what effects does low emission capability have on tubes. It's obvious that with lower emissions the maximum cathode current is reduced. What else changes? Mainly my concern is plate resistance and thus the curves. Is there any difference with low emissions from age and wear, or low emissions on account of sub spec heater voltage? Are curves measured in a low emission situation reliable (at least at lower cathode currents)?

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20th May 2011, 10:34 AM	#2
DF96 diyAudio Member Join Date: May 2007	Low emission is likely to mean that current and gm go down. As mu will remain largely unchanged, the anode impedance will rise. This means that, on average, a triode circuit will survive valve ageing better than a pentode circuit - triode amplification is largely set by mu, but pentode amplification largely by gm.