I just ordered the adaptor from garage1217.
Do you think this tube will be ok?
https://www.thevalvestore.com.au/home/77-6n23p-ev.html?search_query=Soviet+reflector&results=14
that russian tube will give a spotlit treble, a recessed midrange and decent bass in a mhdt dac, i personally think it hurts the sound in the midrange, where the dac should really shine
i would suggest an old stock european 6dj8 equivalent tube from tungsram/hungary or ei/yugo if you are trying to stay at a reasonable cost (otherwise go for mazda telefunken or dutch amperex ones which are $$), these will give a nice lively treble but the midrange will be much more textured and palpable
one other important note... the g1217 adapters have long pins... do NOT insert them ALL the way into the mhdt tube socket, or the adapter pins may damage the underlying socket solder joints ... ask me how i know :( -- instead, look at the pin length of the stock 5670 tube and insert the adapter socket only that far into the mhdt dac tube socket