To all discussing the auto bias situation, I say, go for it. I installed one in my VTA-120, the ABQ, and one in my Marantz 8B, the ABS-Q+, which has its own supply of bias like the tentlabs board. As far as installation, its easy. However, if you want assistance go to audioamp.eu and email Pavel. If you email him a schematic of your amp, he'll redo it to show you exactly how to work it into the circuit.
In my VTA-120 I used a small toroidal transformer to provide the 6.3vAC to power the board because I did not want to use the 6.3vAC from the amp's transformer. In my Marantz 8B I used an even smaller toroidal to power the board because, since the 6.3 volt winding in the the Marantz is center tapped and grounded, and I did not want to lift the ground, I had to do it that way.
None the less, subsequently I installed the 115vAC ABS-Q+ in the Marantz so I don't need to power the board with 6.3vAC. It is powered from the mains voltage, 115vAC +/- about 5 volts, so it is for North American use. There is a 230vAC version available also. The ABS-Q+, as I noted, has its own bias supply, like Tentlabs, so I don't need to use the amp's bias either. Also, both boards are fused on the primary side of their transformers. Installing these boards has improved the sound, and makes the amps that much more pleasurable to listen to and live with.
In the VTA 120 I further installed digital bias meters at the front circular cutouts of the amp. I used a double throw/double pole switch put in place where the cutout on the front of the amp for the stereo/mono switch, which is not used on the VTA-120, would go. I also installed a separate on/off switch on the back of the amp for the meter's power supply so that I can turn the meters off while the amp is still on after I've checked the bias. With the ABQ board it is always spot on; and with the dpdt switch I can check the two back tubes, switch in up position, independently, and the two front tube, switch in down position, independently. In the middle position the meters read zero, but, as noted, when I am not checking the bias I can turn them off.
So, putting the board in is relatively simple. Pavel provided me with redone schematics for both amps. However, the actual logistic of it was a bit more complex for the VTA-120 then it was for the Marantz. The Marantz is all point-to-point wiring, so removing the bias pots from the circuit was easy. Of course I left the bias pots in place for aesthetic reasons, but they are not necessary with the board. With the VTA when I built it, I installed the bias trimpots, all four of them, on the driver board, again for aesthetic reasons, but it was necessary to not install certain resistors, small ones, on the board to remove them from the circuit. This was absolutely not a problem since I can read a schematic. There were other slight modification I had to do to the driver board, but the amp's original schematic, and Pavel's redrawn schematic helped there too.
Anyway, when I last posted here I said I was going to upload some pictures. When I tried, I was told I was to new to the forum to have the privilege of posting pictures. Hopefully I have been on the forum long enough now, though not posting much, to now have that privilege; so very soon I will post some pictures to show the VTA with all the features I have add to it, including the DC heater board I add to it. But that is another story.