Input Grid bias on triode vs pentode

[Tobyk]

Will there be more hum when input grid leak biasing a triode vs. using a pentode?

[martin manning]

This is in the case of a preamp stage? If so, I would say since the gain is higher than a triode, hum might be more of an issue with a pentode, and some small signal pentodes are known for high hum. EF86 is one.

[Tobyk]

This is in the case of a preamp stage? If so, I would say since the gain is higher than a triode, hum might be more of an issue with a pentode, and some small signal pentodes are known for high hum. EF86 is one.

Yes, for the input stage – the old school grid leak biasing method. I think I read somewhere pentodes are better hum-wise in this case because of their higher internal capacitance, thus less Miller effect.. something like that..?

[martin manning]

The pentode's screen grid hides the plate and minimizes Miller capacitance even though the gain is higher. The result is that pentodes do not suffer from high frequency roll-off like triodes do, and make better RF amplifiers.