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Oh yeah, you asked about zeners. As a rule, you use multiple zeners only in series, not in parallel. Since a zener is a constant-voltage device putting them in parallel almost guarantees that one of them will kick in at a slightly-lower voltage than any other in parallel with it. That zener will "hog" the current and the one with the slightly-higher threshold will get less than half the load. Putting them in series keeps the current through each zener the same, in spite of small voltage-tolerance differences between them. We use a series string of five 20-Volt zeners to regulate the negative grid bias for the 4CX250B tube in the Pride base amplifier. Much cheaper than a single 25-Watt zener. And since they spread the heat five ways, no need for a heat sink.

73

[QUOTE="nomadradio, post: 812908, member: 22"] Oh yeah, you asked about zeners. As a rule, you use multiple zeners only in series, not in parallel. Since a zener is a constant-voltage device putting them in parallel almost guarantees that one of them will kick in at a slightly-lower voltage than any other in parallel with it. That zener will "hog" the current and the one with the slightly-higher threshold will get less than half the load. Putting them in series keeps the current through each zener the same, in spite of small voltage-tolerance differences between them. We use a series string of five 20-Volt zeners to regulate the negative grid bias for the 4CX250B tube in the Pride base amplifier. Much cheaper than a single 25-Watt zener. And since they spread the heat five ways, no need for a heat sink. 73 [/QUOTE]

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