[sdiy] Hollow low-pressure ladder filter

[eric b]

>With a forward voltage drop of 10 volts each, won't at least 70+ volts be
required
>for a stack of 5 6AL5s, or am I missing something here?

It might be enough to get usable resistance variation.
Maybe. They vary a lot from unit to unit, brand to brand.

>Maybe try 6AU6s, they are cheap and plentiful pentodes.

Antique Electronic Supply is having a 
sale on overstocked tubes until May 31.
They have 6EA5/EV5 tetrodes 
on sale for 50 cents each.......

very high-gain devices, originally used
in TV RF stages........recommended.

Eric Barbour
Svetlana Electron Devices
Portola Valley CA USA