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I would like to use a D3A or a E810F from a source that is very low level (-70db or so) and very high impedance (700 meg). I noticed that both of these tube have a max grid 1 res. rating of about 500k. How will it effect the tubes operation if I use a 70 meg grid res?Are there other tubes that sound great you could recomend for gain, low impedance and openness of sound? How about between these two?
Thank you!
Follow Ups:
Hi Jor,a good chois for grid leak bias is the EF804S (Rg 22 MOhms).
Never hurts to see how others did it. Might look at 6205, or 6072?? Not a mic guy but I'd think you'd want a tube made for low microphonics in a rough environment.
Russ
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.
Hi
I am building a condenser microphone and would like to use a great sounding tube that is high gain with low impedance like d3a and e810f. Welcoming all helpful advice about tube choice, grid res ratings and the like. Thank you very much! Have a great day,
I hope you're not building a gravitronic detector. I already have that patented.
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