music hall 25.2 DAC mod

It's great to hear positives about this DAC. I've had mine for about 2 months now and couldn't be happier. Tried swapping out the tube for a Matshshita and though the bass firmed up a bit, the top end lost air and life and never opened up. After what I've heard here, I just may try the JJ. With the stock tube and time on my hands, the unit has opened up several times and just gets better. Very resolving, detailed and nuanced. All the air I can ask for and no grain. I can only imagine (and I do, constantly) what some Burson opamp replacements can do along with the EAT tube but what I hear, right now, is simply wonderful.
My only complaint is getting used to the feeling that someone or something was in my room while listening to it: the musicians have a real and palatable presence.

I, too, got a NOS '71 Mazda from Brent Jessee (w/RTC label) and it really transformed this DAC. He said he'd put it up against any EAT valve as they
are reversed engineered replicas built to very high tolerances but can't use
the same metals used in the NOS tubes. Something about the AEC won't allow it.
Now I have no desire to swap out anything else.
I read a blog somewhere else (from '08) that the DACs take about 500 hours
to break in so don't be in any rush to mod this unit. I have about 200+ hrs on
mine and it continually improves. It's like watching a kid grow.
A really good kid.

Being a noob with tubes, please bear with me.
There is a label from Brent Jessee on the box that has a space for Gm1 & Gm2 and both have a 'check' after them.
Tube type is 6922 and brand is RTC, Mfg. = Mazda. Prod. type = 1971 France.
On the tube itself was a slip of paper with the numbers 27-29 &-18/-18.

Hope that helps and that you get the same results as I did.

On an aside, I tried a '70s Matsushita, from another site, that was touted as a great tube (not from that site but from various sites) with negative results: flat, closed in mids and highs and generally dull sounding and this Mazda is quite the opposite. Open, airy, fleshed out (more body), dynamic, very quiet, with decent bass. Almost organic. The top getter is tilted at a 45 degree (I thought it was damaged at first) and kinda looks like how one would wear a beret.
Fitting for a French tube.

Rja,

That is correct.