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Allan
Member
Username: Allan
Post Number: 79
Registered: 2-2006
| | Posted on Saturday, April 22, 2006 - 6:21 pm: | 
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Been scanning the archives to see if I could find the answer, but missed. On amps that uses transistors to drive final transistors (1x2, 1x4, 2x4, and so forth),how does it work? I've seen amps with, oh say, 2sc2290's in them driving 2sc2789's. How does the final stage in this set up take the high drive the driver transistors are putting out? In 1 stage amps these same transistors can take only 4-15 watts maximum input. Get the picture? Seems to me the drive transistors would over-drive the final stage. Just curious.
Pat? Any input, here, buddy? (I didn't say good!)  |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2741
Registered: 7-2004
| | Posted on Saturday, April 22, 2006 - 7:11 pm: |
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1-2879 will take an input of 3 key/10 swing, therefore, 4 of 'em will take 10+ key/40 swing. a single 2290 driving 4-2879's is gonna be 'dumbed down' a TINY BIT from its max of 20 key/80 swing. any mass produced, commercially made 2x4 boxes are SERIOUSLY dumbed down, as the tiny transformers & little wires just AIN'T gonna handle 40/160 input from 2-2290's....why they even bothered....custom/comp amps are built to take more SWING input, so they can get away with what may appear to be too many driver transistors. they will still handle the same dead key input, though. |
Allan
Member
Username: Allan
Post Number: 81
Registered: 2-2006
| | Posted on Sunday, April 23, 2006 - 8:46 am: |
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Pat00 sez... just AIN'T gonna handle 40/160 input from 2-2290's...
On another post, there was discussion about this very same setup with the "Palomar" 900 Hi-Drive, that uses only the 2879's in the final drive stage, and omitting the 2290's drive stage, I assume, for the newer 10 meter rigs that are now sporting them, to take over that duty. So states they will take 100 watts input. Seems like one would have to be careful not to smoke this amp with one of these radios, with the 40/160 output, to drive these amps. Not so much a 'hook it up and go' thing to do, it would appear. Of corse, in all amp applications, you and others, stress the importance of keeping the DK and PEP at or below what the transistors can produce out the other side, driving or driven... |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2747
Registered: 7-2004
| | Posted on Sunday, April 23, 2006 - 11:15 am: |
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while the 900 high drive MAY handle 100 watts PEP input, i would not expect a long life from it. nor would i expect 900 watts. a lot of #'s come from inaccurate meters, poor power READING practices(never read 20 watts on the 2000 watt scale-always read on the LOWEST scale possible), overgenerous manufacturers, etc.
HOWEVER, that is NOT to say that NO AMP will be unable to handle more input then recommended. i have a dx350 that is nearly 25 years old & was REGULARLY fed 50 REAL PEP watts & has lived to tell about it. also a 667v that was keyed HARD to 200-300 watts & swung over 500 due to HIGH PEP input. the internals of BOTH are/were MELTED & BLACKENED from excessive heat-with some heavy duty cooling fans surrounding 'em. i STILL keep an OLD 'space warp 225' amp that somebody blew up maybe 6 times. he used a galaxy dx88(i think) on it & it blew within a dozen keys every time. it just would NOT take 10 key/25 swing-at all! some amps seem to handle excessive input better then others. some swing backwards & sound like junk, others work fine. if you go by the specs of the LAST set of transistors in the line, & back your way through the driver, to the radio, you'll find you get the best sound & best reliability. if you don't want to be fixing things all the time.
i, on the other hand, have a large assortment of soldering guns, irons & tips on hand. as well as a few spare transistors at all times.
1.adjust for maximum smoke
2.repair
3.back down 1 notch
4.try again
5. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1217
Registered: 1-2005
| | Posted on Sunday, April 23, 2006 - 11:41 am: |
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Pat is the Cheech and Chong of RF amplifiers. In the movie Nice Dreams remember the icecream truck they drove around followed by a cloud of smoke? I can see clouds 10 ohm smoke following behind Pat's truck on the freeway!
Just teas'in ya Double 0! I get like this in the morning with to much caffiene.73 |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2754
Registered: 7-2004
| | Posted on Sunday, April 23, 2006 - 2:12 pm: |
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10W smoke IN the truck is....nasty but at least i know i got max output....once |
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