That’s it. They are sometimes known to sing at high frequencies
No need for apologies. I only ask because a few people have reported odd issues and different cells made all well. I wonder if some unprotected cells may be too short to make a good connection? Since this is a series light the double stack can vary by 6mm or more depending on cell choice. Just trying to rule out if it’s truly an issue with the light or more to do with the cells. If what you’ve described and what KB has already suggested already rules that out then please disregard this comment. I fully admit I know little about this higher end of the technical aspects and defer to those with more knowledge. If there is anything you think I can do to help or need to communicate to Simon though please let me know.
Why? When a inaudible frequency becomes audible, usually means something is wrong? Some kind of electrical interference, loose connection, improper grounding, shielding, vibration? Something is making that frequency amplified? Same thing is going on with the K70, some make noise (sing) some don’t. My K70 don’t and I have had other people check it, and why aren’t more L6 owner’s having the same issue? Just saying………
I’m not an expert in flashlight driver topology, but I’ve heard inductors whine in the past in other circuits. Just like humming power transformers. Some hum, some dont. Depends on the construction.
BTW, my Dry whines on the second brightness level. It’s been doing it for 2 years with no ill effects.
Edit: just noticed the Dry even whines in the turbo mode, only when I press my ear up against it. I’m 64 years old so I may not detect what younger people hear. Had my hearing checked recently, and I can still hear up to 14 KHZ
I let Simon know, I am sure that it will be figured out soon.
until he responds, I don’t really feel comfortable opening the innards of the head, and switch, and checking things, he may ask me to send it back for inspection for all I know ( hope not) but if he needs to look at it, At least I have not touched anything that is inside
Anyone measure the voltage where the L6 battery protection kicks in yet? If not, I’ll do that when I have time.
Thought I read 6 volts but I am not 100% sure.
If you test please let us know. Protected cells are recommended
Just received this flashlight and I am impressed with its build quality.
Diggin’ into local online store to get protected 26650, can only found this. After I tried, a bit too long and flashlight can’t work properly (only two modes available: low & med) 
After reading this thread, I think I’m gonna use unprotected batteries with proper precaution.
If you bought one of those, and it’s too long, you might consider stripping it of it’s pcb. The protection circuit is limiting it working with the higher demand of the driver anyway, or so it would seem.
Thanks for the head up, Dale.
I have no other 26650 flashlight (yet) so I think that’s what I’m gonna do with these batteries.
The light design is nice and I’m looking forward to smooth reflector for throw as I got too many flood lights but this is not easy to achieve due to the Cree size .
Perhaps push this light further say 7amp to compete other lights with temperature control/ step down ?
Will definitely buy 1 or 2 if it can throw close to acebeam k70 and it will be a sale winner 
If that’s not something you’ve done before I would use caution and do some research first on how to do it without endangering yourself. Don’t want anybody getting hurt now.
J-Dub74, any one compare the L6 with 5700K emitter vs 5000K you know of?
Not that I know of though I’d like to see that comparison. Heck I’d like to see them all side by side for that matter.
BEAST has arrived!
Took a test with new Fluke, stock leads, Efest 4200mAh batteries: a bit over 5A draw. Whew…
Received my L6 5A yesterday, put two Shockli 4200 mAh in and Bang! Love that tint and output. It is making a little less lumen than the S70 but more throwy than the S70.
Sad that my 5200 mAh protected battery did not fit. I thought I will be able to modify the springs to get them to fit lIke my S70.
Nice! What tint did you get?
I got the 5000K L6, and I have a Fluke 289 DMM, and the new green Efest 4200mAh 26650’s Haven’t checked the current yet. But I will soon. Which Fluke did you get?
Edit: Just checked. I get 5.18 amps on turbo. That’s with the stock Fluke test leads
Seems to me, having a lightbox to watch the output numbers closely, modding the two lights shows where the real differences are. Bumping up the S70 shows that it gets hot faster and the lumens fall amazingly fast. The L6 seems to be able to handle some light modification with more grace. I don’t think either of them are great over 7-7.5A, but down around 6ish, I like how the L6 performs. That’s just my observations on my lights, YMMV.
It arrived!
It’s huge!! Too tired now, but hopefully will have some time soon to stuff around