This Carr Mini Mercury recently came through for new tubes, biasing, and tune-up. It is a nice tagboard build, and a great sounding amp! At first glance, the wiring may appear chaotic, but everything is twisted tightly and routed sensibly. There are no issues with noise or oscillations. I absolutely love a tagboard build when it is done correctly.
The attenuator switch on this one had become crackly, but a quick cleaning solved that issue. The switch lets you select outputs of 8, 2, 1/2, or 1/10 Watts. I question the real usability of the two lowest settings, as they lose a lot of the high end (especially the 1/10W setting). But the 2 and 8 positions are very useful, and in combination with the boost switch, allow you to achieve a wide variety of classic amp tones. I was pretty impressed with the versatility of this amp.