[Ericus Rex]

I understand tube principles, electron flow and anatomy.  But I've never heard exactly what grid leakage is.  I assume some electrons are getting 'lost' but which grid(s) are leaking and leaking to where?  And will grid leakage actually harm the host component?  What does it do to the function of the tube or resulting sound?

Thanks in advance for your patience with me and my 'basic' question 

[Dougl]

Basically, electrons can build up on the screen grid.
If the path to ground is too high resistance, this charge can alter the bias, causing more current to flow in the tube.
This can be exploited to have both grid and cathode at ground level using a 1 meg resistor(not something I advocate FWIW),  or it can destroy output tubes that run away if the grid resistor is too large.
The data sheets may give a maximum value.

HTH

Doug

[Steve]

I understand tube principles, electron flow and anatomy.  But I've never heard exactly what grid leakage is.  I assume some electrons are getting 'lost' but which grid(s) are leaking and leaking to where?  And will grid leakage actually harm the host component?  What does it do to the function of the tube or resulting sound?

Thanks in advance for your patience with me and my 'basic' question 

Hi Ericus,

A small amount of no. 1 grid current is always present to some degree for several reasons; residual gas and proximity to the heated cathode contribute etc. Some gold plate the 1st grid to increase its work function and reduce grid emissions. Tube data sheets usually give the maximum grid circuit resistance for a given tube under different conditions of operation.

Even new, no. 1 grid current commences a few tenths of a volt negative with respect to the cathode. Some cathode material deposits on the grid and increases grid current flow during the life of the tube as well.

In no particular order, no. 1 grid current can lower the input impedance. Can change the operating conditions resulting in increased distortion. Another problem mentioned is thermal runaway, destroying the tube.

This is not an exhaustive explanation but hopefully easy to understand.

Hope this helps. Cheers.