I've looked for/at the smallest ammeters and (thus far): haven't found anything I could mount anywhere on my SLMs' chassis, for the convenience of not reaching for my Fluke.
Hanging a couple on the amp stands and hard-wiring to the Bias jacks, would be a possibility, but: I'm SO lazy.
Besides, it seems: with a good quad of output tubes in each monoblock, their relative biases seldom change. Only: slight bias variations, consistent/the same in both, according to what's coming from the wall.
The SLMs were my step, following the Rocket 88, which didn't have the juice to satisfy my SPL Jones (inefficient speakers, at the time). No need to look further, as the SLMs' excellent transformers and circuit design made adequate power and the realism/presentation I sought, an easy reach, with judiciously chosen parts.
They were treated early on, to better RCAs, 5-ways and IXYS HEXFREDs. Since: every cap has been upgraded (ie: Duelund cast-PIOs for coupling, ClarityCap ESAs in the B+, etc ).
Of course: the optimum, NOS 6SN7 search was another enjoyable, illuminating and fun-filled journey.
Yeah: I'm FULLY invested in the SLMs, with NO regrets!
Happy listening!