[Elecraft] BL-2 Balun Heating

[Gary Winkelman]

I recently built a BL-2 Balun.  It is connected between my Palstar AT1KM 
tuner and my doublet antenna.  The antenna consists of a 100' wire up 
25' and fed by 95' of 600 ohm open wire feeder.  I'm using the 1:1 
setting on the balun.  There is a 4" section of RG-213 between the balun 
and a coax input of the tuner.  I'm driving it with 125 watts from a 
TS-850.   After no more than a few minutes of CW or RTTY transmission, 
the balun is too hot to touch, the SWR rises and the power goes down.  
The balun is obviously saturated. 

Does anyone have an idea how I can reduce the overheating?  I've tried 
adding a heat sink but it doesn't make any difference.

Tnx for reading!

Gary  N2UM