Tube Rolling Advice for the Backert Labs Rhumba Extreme?

Tomorrow I have a Backert Labs Rhumba Extreme 1.2 being delivered, which has been upgraded by Backert to 1.3 specs. It will be driving the Luxman MQ-88uSE and the front end is a Qutest with M Scaler (Innuos Zen MK III server/streamer). Speakers are La Scala IIs, placed about 15' apart in the corners at a 45º angle. Soundstage is excellent and expansive with remarkable placement of instruments across the sound field.

If all goes well it will be replacing my L-509X, which is currently only being used as a preamp for the MQ-88uSE, so it’s being underserved in my system and will need to find a better home.

I am interested in any advice about tube rolling with the Backert Labs pres. With the Chord digital front end, I am getting a very layered, dimensional, detailed sound and thanks to the Qutest filters I’m able to adjust filters to best match the amplification. The MQ-88uSE has a gorgeous, full, warm sound and right now the 509X’s solid state pre is giving a nice sharp, detailed, and dynamic profile to sharpen up the tube sound a bit.

I don’t want a syrupy or bloated tube sound, more airy and detailed on the top with holographic imaging with solid heft on the bottom end. I’ve replaced the preamp tube in my Cronos Magnum II with a Cifte and was really happy with the impact on the sound.

The Backert comes stock with new Mullards, which I expect may have a slightly warmer sound than what I’m chasing.

Any advice?

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I just stick with the exact tube type the component came with or the mfg. says is safe.    

The are not the same bias.   There is no direct sub for a 12sn7 according to my Hickok manuals.  There are many great 12au7 still out there as NOS and several new options.  It doesn't even make sense .

Personally I treat this book and it's addendum like they are Gospel.   If it's not listed in that middle column I would advise against,  do so at your own peril.   I used that guide and other tester documentation long before I got a tube tester.   

I've never had a component damaged by a tube and I think it's because I never took another enthusiast's word for it that something was a good substitute. 


On that particular list the middle column should say Acceptable Sub , not direct sub.    Direct sub narrows it down to 5418 6189.  Those are the same tube but ruggedized 

I ran into this when searching for an E180F tube.   Many varieties,  more than you would imagine actually and I checked with my Amp's mfg. and he said 7788 was fine .   So I always do that.   I reached out to Mike at Quicksilver a while back just to check if 5751 were OK and he said no problem.  So that's really who you should be asking, not the dealer.