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The 20 amps per transistor rule of thumb will certainly insure you purchase a big enough power supply. This rule really only applies to single ended RF stages where each 120 watt transistor may draw 20 to 25 amps max for a 2SC2879. The situation is quite different in most amps where you have pairs of transistors operating in push pull. In a push pull bank of two 2SC2879 transistors it is not possible for it to draw 40 amps because only one transistor is actually working at any given time (excluding slight bias current if any). In fact if you reach over 25 amps on a push pull pair of these transistors one is almost certain to fail. Most HF radios that used a pair of 2SC2879 were only fused at 25 amps. About 5 amps for the radio and drivers with 20 amps for the pair of finals.

[QUOTE="Shockwave, post: 240076, member: 10882"] The 20 amps per transistor rule of thumb will certainly insure you purchase a big enough power supply. This rule really only applies to single ended RF stages where each 120 watt transistor may draw 20 to 25 amps max for a 2SC2879. The situation is quite different in most amps where you have pairs of transistors operating in push pull. In a push pull bank of two 2SC2879 transistors it is not possible for it to draw 40 amps because only one transistor is actually working at any given time (excluding slight bias current if any). In fact if you reach over 25 amps on a push pull pair of these transistors one is almost certain to fail. Most HF radios that used a pair of 2SC2879 were only fused at 25 amps. About 5 amps for the radio and drivers with 20 amps for the pair of finals. [/QUOTE]

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