Cathode Follower and PI tubes- tonal impact?

[59Vampire]

How do these positions affect tone? Does it matter what type of tube is used ie, NOS vs New manufacture? What does a cathode follower and a Phase inverter do?

Thanks for the schooling. The reason I ask is that my PI went bad and even tho I have a stash of NOS I was under the impression that it did not matter tonally and I threw in a tested chinese. Thanks.

[conundrum]

To transfer the most power from one stage to another of a tube amp you want matching impedances. A Cathode follower brings the impedance of a previous stage down to match the input of the following. It dosen't ad gain per se, but it makes the power transfer more efficient.
In a push-pull amp you need to feed the transformer with 2 identical signals that are out of phase. This is what a phase inverter does. Takes a signal and spilts it into 2, one of them being out of phase.
Both of these tubes effect tone, much moreso when they are driven to distortion.
Sidenote. It is very important to have a quality tube in the Cathode follower position as newer tubes don't seem to take high voltage on the cathode very well.

[59Vampire]

Thanks for the info. The amp in question is a modified 18watt tmb circuit. I will swap out the JJ cath for a telefunken.