The only thing I do every 4 months or so , is to scrape the carbonized kevlar wick off the resistor and put a new one..
Sadly enough; they are also hard to find on this side of the pond.
I bought mine from this supplier in U.S. http://www.surplussales.com/Resistors/W ... 0-169.html
They are out of stock for the 14 Ohms 1 Watt that I was using, so I ordered some 14 Ohms 2 Watts...
Although their prices for parts are reasonable; they make quite a bit of profit on their shipping costs...
My last order was for 20 resistors at $1.00 each (= $20.00) and the shipping costs from U.S. to Canada are $30.00...( so the resistors cost me $2.50 a piece)...
Shipping out of the continent must be astronomical...

