The MG Head comes with a 12ax7. Has anyone tried other base 9a tubes (ea. 5965,6211,5814,12bz7,12az7,6829,...)?
Is it SAFE to try the more than 40 variations?
Could it cause any Damage to the headphone amp?
You CAN and WILL damage teh unit if you tuberoll in the wrong pair of tubes into any tube amp!!! Make sure you do a search on the internet and come up with a list of all the variables that work with this particular family of tubes.
Here's all the ones I know: 12ax7, 5751, 12au7, ECC803S, ECC83, 7025, ECC82, 7316, 6189, 5814, and so on and so on. Find people selling these tubes on the net and look at what they list as drop-in replacements and you shouldn't go wrong.
When in doubt: ask before you buy or try something out!!!! An amp is an expensive thing to fry!! Take a second and make sure a tube in question works as a drop-in.