The amp (Valvestate VS100R with ECC83 Glass Valve) packed in a few months ago. Two of the 4 darlington transistors (2xBDV64 & 2xBDV65) had gone short circuit, also taking out the 1A anti surge fuse. I replaced them (using heat sink paste as well) and it happened again, so I replaced them once more and left the amp on (guitar & effects unit unplugged / overdrive off) to eliminate external possibilities. After about 15 mins I measured the temperature of the transistor heat sinks - 3 were 40-50deg C and 1 was cooler. After an hour I went out of the room for 5 minutes and returned to find it had blown again. The heat sinks were hot - one of them was 100 deg C. Any ideas what could be causing this? The amp is a few years old but hasnt had a great deal of use. Thanks in anticipation.
- posted
15 years ago