TUBE BIAS, socket to me!

In my long experience, tube amplifiers that require periodic bias adjustment typically provide both external test points (female jacks where you stick the pos and neg meter probes) and externally accessible potentiometers with which to do the bias adjustment.   Some owners of ARC amplifiers have already mentioned this. Some brands (like Atma-sphere on at least some of the model line) even provide a built in external meter, so you don't need to own a DVM, etc, in order to adjust bias. Another large set of tube amplifiers have an autobias circuit built in, which automatically senses a drift in grid bias voltage and compensates for it, until the tubes themselves are worn out.  Your Cayin amplifiers are unusual in that they apparently do require manual adjustment of bias, but you seem to have to open up the chassis to get at the adjustments.  That may reflect their "made in China" provenance, where perhaps the liability laws that provide legal recourse for persons who are injured by electrical shock whilst biasing are less stringent.  (But perhaps the US distributor could be made liable in the US.) So just take the warnings seriously and proceed carefully.  I always keep one hand in my pocket when working with power on, to remind myself never to grip the amplifier with two hands, which could send a shock across your heart muscle.  It doesn't take much to be lethal.  I don't think you need a non-conductive screw drive blade so long as the handle is non-conductive.  But it couldn't hurt.

Maybe Ralph can chime in, but I have no idea what is being adjusted to 0.4V in your amplifiers.  Surely that does not represent grid bias voltage (between grid and ground or grid and cathode) for an output tube.  Perhaps you are adjusting the voltage across a fixed value resistor which in turn affects bias current.  Also, you need a fairly good quality meter to be accurate in that under 1VDC range.

Now your talking electrocution precautions? Come on.... it can’t be worth it.

i guess as a physics lab hobby, its OK- I’d rather listen to music than play in the lab with tubes. 
I had physics lab in college 40 years ago. No desire to go back there.

@elliottbnewcombjr Before the owning my VTL 450's I had VTL 300 Deluxe mono blocks and they were not Auto Biasing so I feel your pain!

Soko, Read what I wrote.  Elliot's Cayin amplifier is the only tube amplifier I ever heard of where the manufacturer actually invites the user to enter inside the chassis, under any circumstances, let alone when powered up.  All other (US-made) tube amplifiers I know about will usually carry a warning NOT to open the chassis, ever.  Usually the warranty is voided if one does that.  Typical tube amplifiers can be re-biased externally with no risk, or not at all if they incorporate an autobias circuit.  Got that?
It so happens I am a DIYer, so I often do work on my amplifiers and preamplifiers, usually for fun and to satisfy my interest in electronics.  But I didn't even try to do that until I had a solid knowledge base, in part to keep me safe.

Gotcha @lewm. So what user involvement would be involved with normal routine maintenance/upkeep of tube equipment of 2000 vintage or later? Testing, rolling, cleaning, biasing, replacing, etc.

For analogue, I have to get a new stylus (or cartridge) every 2-2500 hours of use.Maybe change a belt after 10 years. I’m not aware of direct drive tables needing anything.