Ideal Location For Void Key Farming

[(PSN)Hollow118]

So with the new primes out, I've been looking to farm em. Problem is that I kinda forgot where to get the keys I need. So I'm here to ask: What is the best node to farm these Tower keys from?

 

 

Tower 1

Tower 2

Tower 3

 

I am just asking for where to get those Tier of keys, not any specific ones. I know all about T4 but I need good nodes to get other keys from (especially the Sabotage keys)

 

Thanks for the help.

[M4TERIAL]

If you do defend mission you can get some. Otherwise go to wikia

[Grobbus]

Excavation is the way!
Any Excavation mission can grant from T1 to T3 keys after 3rd or 4th extraction.
Cambrai on Earth is quite a good place to go solo as enemies start at really low level and you can solo to around 15 excavators just fine. That's 4-6 keys per run which lasts no longer than 30 minutes compared to Survival and Defense it's the best and efficient way to obtain those keys.