I want to build the "Death of Zen" audio amplifier and I found a video on YouTube of someone who built it and used a 10 mH choke for smoothing of the pulsating DC. I found an old transformer from an audio amp (line 6 low down studio 110) and I found a spot that is 10 mH on my LCR meter. Would this be suitable?
A transformer is made of (at least) two windings that are coupled together through a ferromagnetic core (iron plates). A choke/inductor uses exactly the same principle, but only has (usually) one winding. Both transformers and inductors need not to have a core - may be simply a set of wire loops (aircore). Such device is not subject to an effect called core saturation. This prevents transformers and inductors with a core from functioning properly when forced to conduct excessive amounts of current. This is probably not your case though.
The inductor in the video the labeled "10mH 5A". That means that it has an inductance of 10mH at 5A. Above 5A the inductance decreases as the electrical steel core goes into saturation. So, in practice you can use this inductor model with currents of up to 5A.
Though an inductor looks very much like a transformer lacking one winding, there is a fundamental difference: An inductor core has an air gap and a transformer core has not. This air gap length is one of the most critical quantities when designing an inductor. To make a long story short, with increasing air gap length you get
- less effective permeability (leading to less inductance) and
- more saturation current.
So without an air gap (as in the transformer) you get very little saturation current and the core could saturate at a few milliamps, depending, among other things, on the core cross section and the number of turns on the winding you are going to use.
In summary that means that using a transformer instead of an inductor might work if you stay far away from the rated current of the winding to be used, but in practice this does not make much sense as the transformer is severely under-utilized and thus too big and too expensive when compared to a proper inductor.