Is this "old tube" a C&L or something? your description is not clear to me at all.
If you're talking about taking the electronics out of an OEM meter and putting it into the housing of another brand and size then it will not work. Not unless the housing that you're putting it into has a sample tube that runs in front of the sensing element (like a C&L meter). OEM meter electronics are calibrated for a specifically sized opening. Changing the size of that opening changes actual mass of air that's able to go through that opening. OEM meters are designed to measure air mass through the opening of the meter housing that they came with.