Runing MTH engines with vintage Lionel transformers

I don't know for sure, but I would think so. I run my TMCC PRR E6 with either a Lionel "S" type, Flyer 15B or MRC 027, and they all seem to be fine. I'm sure someone with more knowledge will chime in soon...

Mark in Oregon

You shouldn't have any problems at all with a KW...and the ProtoSounds should work just fine.  Funny; I just posted a question about an MTH BL-2 of mine that ONLY seems to work with old Lionel transformers!  Good luck-

Here's a photo of the transformer compatibility chart that MTH provides in the operators manual.

If it is not in the chart,  you should not use it.

The MTH locomotive is designed to operate on AC and the above mentioned transformers you mentioned are AC current therefore, they are just fine.  However, with these older transformers, it would be wise to place a circuit breaker between the track and the transformer because of power spikes which are harmless to older equipment but can be devastating to the electronics in these newer models.  I run all of my TMCC, Legacy and DCS using an original Lionel ZW and I have never had any problems. These circuit breakers can be purchased at any auto parts store such as Auto Zone, Advanced Auto or O'Reilly's Auto Parts. You can purchase the circuit breaker holder there as well. After this, you are good to go. 

A circuit breaker won’t stop voltage spikes. It protects wiring. A TVS will protect against spikes. 

I am running Lionel and MTH engines with Marx transformers...

Those old Lionel transformers are fine, but should be protected by external circuit breakers.  For a postwar ZW, I wouldn't exceed 10 amps drawn from the entire transformer, to protect the transformer.  John H is correct in his observation