Tube DIY Asylum

Posted by Mahatma Kane Jeeves (A) on March 10, 2007 at 04:51:33

In Reply to: Exceeding Max Grid Resistor Value posted by YoungFred on March 9, 2007 at 15:39:41:

Horses for courses. These are pretty poor tube choices for a high impedance source. You want something with very low grid current and low capacitance. You don't need high transconductance or low equivalent noise resistance.

That's half the battle. At these impedances, you'll need things like active guard rings, some air construction Most boards will be far too leaky), and bootstrapping techniques. Not at all a trivial project, and judging from the question, not one likely to succeed for you. I've been doing this stuff for 40+ years and it would be a pretty daunting project for me.