Is there a standard HOT transistor for monitors?
“Anyone like to comment on BU508’s, they should be to the same spec. and born equal. My experience has been that different manufacturers BU508’s behave differently. One make will fry and last about 3 weeks, put in a different make, no circuit change, and it runs cool, and is still running 3 years later. Price doesn’t seem to be a guide, a $1 one may run cool and have no mfr. code, a branded one cost more and run hot.” Yes, here you have the problem exactly! There is such a thing as component spread. Base drive must be optimized for the whole range of gain within a type. That range can be so large that at the limits of the spread the dissipation can still be too large. The reason is that the device with the largest gain will be overdriven, causing a tail in the current at switch-off, whereas the device with the smallest gain will be underdriven, causing it not too saturate enough. Each condition can be easily viewed on the ‘scope. By varying the base drive you can minimize dissipation.
