Interested in hearing about tube rolling experiences with the Orchid and other MHDT dacs, namely, the specific comparative sonic characteristics of the various 396a, 5670 and other compatible tubes used in the output buffer. My only experience is with the WE396a that Linear Tube Audio installed in my new Orchid.
@pmboyd   Thanks. Yea I have bought from Brent in the past. Got my WE 396 D getter from him. Looks like he is out of stock on most of the tubes you mentioned. He has some of the E88CC / 6922 Siemens, West Germany made, 1960s wide getter support post, gold pins in stock. Might try those. Need to see if the “ the Getter support post” is a wider tube than what I’m currently using and if it will fit (with adapter) into my Orchid. 
gelle... other dealers will have the Siemens tubes and they regularly come up on Ebay. "Farawayfinds" on Ebay has an excellent selection from the 6922 family. I have the Orchid as well and all the flavors of 6922 fit comfortably with a pin adapter. The Garage17 adapter is highly recommended.
gelle... I have several NOS Siemens e88cc for sale. PM me if you're interested.

after reading all the info on the mhdt I borrowed a friend’s solid state Constantine and went out and bought the Orchid

your sixmoons review and this hilarious review of multiple mhdt dacs where very helpful

I picked The Orchid -  a gorgeous schoolteacher. Sophisticated, tempting, and, romantic.

I just started breaking in the dac 4 days ago.

My friend found me some NOS Heintz and Kaufman 2C51 gammatrons

just breaking one of them in

thanks to everyone

I know this thread has been dead for a while, but I thought I’d share a report on my tube swap, which was inspired by landing here through a search.

I lived with my recently acquired Orchid for several weeks with the supplied GE 5670, but after discovering this thread I was inspired to try some tubes from the 6922 family. I ended up with a Siemens A-frame E88CC (using the Garage1217 adapter which works great). The Orchid sounded nice enough with the GE 5670, but the Siemens created a shocking improvement. At the risk of sounding like a generic audio review (but all true), what I’m hearing is a greatly expanded and precise soundstage, previously unheard air in voices, and elements in recordings that I had no idea were there (for example, the birds singing in the intro section of the Latin Playboys track Lemon n’ Ice). Bass is very good with no exaggerated plumpness.

The only caution is that the Siemens tube is taller than the 5670, and with the added height of the adapter it protrudes through the hole in the top of the case, maybe 5/8" or so.

I’m listening mostly to TIDAL Masters via the TIDAL app on a MacBook Pro. If anyone is curious, associated components are a Simaudio Moon SE integrated, ProAc AC 100’s (bi-wired), Schitt USB cable, Audience interconnects and PowerChord, and Mapleshade speaker wire.