Looking at the pics, I think there should be room for a G7-circuit in there.
And after all, 150$ is not expensive for a mic housing (with room for tube socket), cable, and powersupply.
We'll need a picture of the capsule if we have to guess on it's sonic qualities.. Pictures of the electronics tells little about this..
The 7025 (ECC83/12AX7) is not a good tube for microphones to say the least. But it's cheap, and it's a tube alright, so it's used in a lot of chineese mics.
Jakob E.