Well I don't know how many normal bias only SRM-727s exist, but I have one. I got the bias board built and installed today. I'm still waiting for one of the resistor values to arrive here, so for the moment I've ghetto rigged a couple of 100K resistors in series to get 200K on the first resistor, and I've switched the second resistor in the divider to 300K because I needed some for my SRX plus build and I figured I'd kill two birds with one stone. B+ runs a little hot on my amp at 365v so all together this setup yields a 225v Bias. I've got some 165K resistors enroute to replace the rigged 200k resistor on the input side so the final board should yield around 235V bias which I'm thinking will be just fine.
The board is mounted to the side of the chassis on some nylon standoffs. Ground and B+ were tapped off of the test points on the board as indicated in the picture below. For ground you could actually just ground to the chassis using brass standoffs and connect ground on the bias board to one of the standoffs. I didn't have any brass standoffs so I just ran a wire for ground.
She's powered up and my Lambda NBs are singing with the amp completely untethered so I'm happy. Mod success! If anybody else wants to build a bias supply like this the above schematic and values are correct as confirmed by spritzer.
I'd also like to amend my previous comments on the sound of this amp. It's been a slow burner for me, but I've really warmed up to the sound. It's a little warmer than the SRM-1 MK2 which I think in short term A-B testing makes the 727 sound a little veiled. But actually all of the detail is there, it's just not as in your face as with the SRM-1 Mk2.
I'm not great with all the audiophile lingo, so it's tough for me to describe exactly what this amp does, but I guess if I had to generalize I'd say it sounds more natural and effortless than the SRM-1 Mk2. It's strength is especially apparent with percussion instruments. I've listened to this amp for around 20 hours at this point, going through a significant chunk of my music collection that I'm really familiar with, and I prefer it's presentation over the SRM-1 Mk2 on everything I've heard so far.
Well I think I'm done here, this is my new main amp, at least until I build the SRX Plus, but that will probably be a while.