For those interested in the 'math(s)' (the Europeans and some Canadians pluralize it????), it kinda goes along like this.
(for biased amplifiers)
TOTAL CURRENT DRAW
(power out X 1.4 = power in ) / voltage at COLLECTORS!!!!!
That goes for a STRAIGHT amplifier, not one with driver(s) in it.
IOW, a 2879 will do about 150 watts PEP. 150 X 1.4 = 210 watts input. Divide that by 12 (typically that's the voltage you'll find on the collector of a 667, when run from a typical power supply or in your 'AVERAGE' installation in the mobile) and you get....... 17.5 amps of input. Keep in mind, those shitty fuseholders in a 667 are ONLY UL RATED for 15 amps!!!!! Not the 30+++ that go through there (incidentally, UL ONLY rates the auto glass fuseHOLDERS to 20 amps.... Even though they MAKE a 25-80 amp fuses (I have them all), the HOLDERS are only rated to 20 amps, if they grip the fuse. If it's a SPRING LOADED holder, it's 15 amps).
4X17.5 = 70 amps. That's the 2879s draw.
The DRIVER is another 15 or so amps. It (IN THE TEXAS STAR CIRCUITRY) does 70-75 watts PEP.
75 * 1.4 = 105 watts input
105/12 = 8.75 (round it to 9).
THESE NUMBERS ARE FOR A PRETTY MUCH STOCK RADIO DRIVING YOUR 667. If you have a dual final radio, hotrodded finals radio, 148 or other chassis with NPC, Negative Peak Limiting or other assymetrical modulation or overdriven condition, then the current draws above INCREASE, especially on the DRIVER side.
So, with a stock radio driving a 667 at normal levels, you can expect a 78.75 amp draw. This assumes a typical electric system, typical install, typical smaller gauge than necessary wire, etc. If you run oversized wire, have a big alternator, etc... You're not going to increase the efficiency MUCH (maybe a couple percent), BUT, you INCREASE the collector voltage, and that's what REALLY matters.... If you can get 50 percent more voltage, you get double the watts! The fuseholders on ANY Texas Star 4 transistor or larger amplifier HAVE GOT TO BE RIPPED OUT. Then replace the power wire with a MINIMUM of 8 gauge for EACH bank of transistors (with the fuseholders out, magically, there are 4 holes in the back for the pair of grounds and pair of positives! Tie both positives and negatives in the amp together to prevent ground loops, etc. Put a LARGE AGU fuse AT THE POWER SOURCE if your in the car, or use the power supplies internal, if you feel lucky
This usually garners an ADDITIONAL 100 WATTS OR MORE OF OUTPUT, and you didn't increase distortion or overdrive much at all.... (the driver gets a bit more output, but hey....
.
If you use a class C box, battle box, etc., then instead of 1.4 above, you should use 1.25 to 1.35... They are more efficient, usually in the neighborhood of 65 to 75 percent.
Another thing to keep in mind is this: The amplifiers are MOST efficient at FULL PEP OUTPUT. Just because you're running your 4 pill at 45 watts of carrier doesn't mean it's pulling 4 amps!!!!!The efficiency suffers as you lower the power... SO, it does NOT always follow that a lot of 'swing' will keep the amp cool.... The amplifier creates the LEAST amount of heat at full power, IF the amp is installed and working correctly!
Hope this helps you, and anyone else that might ask the same questions. The numbers are pretty tried and true, and if you doubt them, I'd suggest a perusal of the Toshiba, Motorola or Thompson spec sheets, they pretty much agree with what I stated, with exception of power levels: The mfg's rate the transistors at a lot less than we typically see out of them.
--Toll_Free
