I replaced the volume pot on my tube preamplifier.

After reading this post, i checked the motorized volume pot on my LTA MZ2 and it appears to be the RK50A. And it's well under $10k. 

The only MZ2 pics I see online clearly show an RK27 - some motorized, some not. An RK50 wouldn't even fit in there without a motor - it's massive. IIRC motors for RK50 have to be custom made; VAC is the only one I know of doing it in their preamps, which start at $30K. Never heard of an "RK50A". If you're seeing a huge shiny brass cylinder, then it's definitely an RK50.

Getting a great sounding analog volume control with good granularity (at least 40+ steps) and reasonable price is hard enough. Adding motorization / remote control just adds to the challenge. No wonder some (like Audio Research) have gone to digital chips. Khozmo Poland is worth a mention; they produce some very good looking analog volumes w/ controllers, high quality resistors, and fine-grained steps (60+). Lots of flavors to choose from: Shunt, Ladder, Stepped. "Ladder" sems to be the most premium of discrete options. 

Verified good sound:

• TKD 2CP-2511 
• Alps Black Beauty RK40
• Alps RK50
• Stepped & Ladder attenuators (DACt, Goldpoint, etc)
• Khozmo? (haven't tried yet)

@mulveling 

I was going by the label on top that shows

50KA X 2

I this to indicate some stereo version of the RK50 but I may be completely mistaken. One can hope. 

I was going by the label on top that shows 50KA X 2

@mashif

That’s a specification - 50,000 ohm input impedance, x2 for stereo (2 gang) - not a model number. If you were looking at an RK50 model you’d think "wow!" - it’s massive, shiny, beautiful and gold :) 

The RK50 doesn’t imply 50,000 ohms either (though that is a very common choice); it comes in a few different impedance values. 

Yeah, it's a $16 pot available everywhere, probably on par with the 27. But the RK50 is about 100x the price, $1500 or so. So there's another reason for an upgrade. Oh well. 

@noromance Thanks for posting about this! I built a Waynes 2018 preamp, a DIY design from the good folks at Pass labs that I put an Alps 27K in and it is good. But you and the other contributors here have given great leads on what promises to be a significant upgrade. Thanks too to @mulveling. I don't think I can swing the RK50 but the Alps RK40 looks doable! Great stuff.