Quote:
Originally Posted by G8HQP Dave
You need to bear in mind the difference between a substitute and an equivalent. A substitute has roughly the same pinout and sufficiently similar characteristics that it will work reasonably well in most circuits; someone trying to sell you a substitute may stretch the truth. An equivalent is almost the same thing as the original; it could be identical, or only have minor differences which will almost always be of little consequence in almost any circuit..
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By your definition, I would say that most equivalent lists are substitute lists and in many cases they are not even a good substitute with different heater currents and characteristics. Worse than that, manufacturers changed the performance of their valves and I have an example of a 30's Pye set with a label saying you should not replace a particular valve with a newer version of the same type without circuit changes.