Audiophilepure

https://www.whathifi.com/us/reviews/mcintosh-mha200

There are valves at the heart of this unit – four in total – made up of a pair of 12AT7s in the driver stage and 12BH7As in the power stage. These run warm and are usually protected from prying fingers by a removable cage. Next to the valves is a trio of transformers: one for the mains and two that couple the amplifier’s output valves to the connected headphones. As with most valve products, a certain amount of care has to be taken over matching. Here, that takes the form of a front panel control that switches between four load options: 32, 100, 250 and 600 ohms. Simply switch to the one that’s closest to the nominal impedance of your chosen headphones for the best results. There’s no harm in trying an alternative setting, and it can be fun to try, but we would be surprised if doing so leads to a better sound.