Hi,
I've just brought the Sennheiser HMEC 25 KAL, by mistake off ebay - they are great headsets and work great on the 737-800... BUT... the ANR takes power directly from a 28v DC supply from the aircraft - my company doesnt have this supply to the jack points. I just assumed they did, so the headsets work but the ANR does not.
What you need is the HMEC 25 KA (battery power as opposed to DC a/c power). Are you sure the ANR on the TELEX 850 works on the 737NG? or is it just my company 737 that doesnt have the DC power?