DH220 electrical hazard found and fixed
This may be of use to Hafler users.
Back in 2003 one of my DH220s began to inject hum into the rack of hifi
gear, it seems that one of the thermal breakers:
a)blew a hole through its side wall, and
b)shorted a (230V over here) AC line to the case.
c)killed a GameCube
The part is marked Elmwood Sensors 87-232 L167 82/N.
The amp case and audio grounds became shorted to one side of the 230V
wall power. This is very dangerous and both sensors must be replaced
asap. (The other one is just as old).
1.If the sensors seem OK, slip in a TO-66 insulating sheet, with
heat-conductive paste on both sides between sensor and heatsink.
2.replace the 6-32 screws with nylon screws to avoid connecting the
sensor flanges to the heatsink. You can reuse the star lock nut.
If the sensor plastic looks dried and cracked, replace them with e.g.
Honeywell/Elmwood temp sensors art.nr. 2455R-01000075 80C +/-3% and
use an insulating sheet for safety. The 80 degrees Celsius is important.
If the sensors trip often, mount some sort of fans near the fins.
I love and use my Haflers every day. With Dahlquist DQ-10s and DQ-1Ws.