Total posts : 45366
One indicator of abuse is discoloration of the paint on the toroid. This was observed with the output filter toroids in my Ramsey AM-25. Initially, this was operated as detailed in the instructions and doing so resulted in discoloration of the PC board under the power transistor and the output inductors. The toroid color darkened quite a bit but it is unknown if the properties changed. It would seem that if the paint darkened then the toroids were operating at a temperature higher than 80 C as mentioned above.
Subsequently, the toroids were replaced with a more suitable type and the power input was lowered to 100 mW and there has been no problem since.