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Old 30th December 2003, 11:22 PM   #1
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Question amp schematic

hello,

what do you think on this amp schematic?
it's original a phase linear pl 400.
i've here nearly the same but from a german company called solton. there it's sta800.
i've edited the schematic, so that it's like my amp here.

my question is if i could use mje 15031 for q11, q12 instead of these unknown 2sa116x? and if q10 and q5 could be a mje340 and q7 a mje350.

thx a lot
best regards
andreas
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Old 31st December 2003, 12:36 AM   #2
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AS per my experience u can use the above mentioned substitute of transistors very well, but need to change the baising accordingly. Simply rebais the amp with substituteed transistors
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Old 31st December 2003, 08:21 AM   #3
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Question rebias

thx a lot,

but how?
Itis enough to turn the bias-trimmer or did i have to change any values of some resistors? or something else?

thx
andreas
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Old 31st December 2003, 08:45 AM   #4
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You should be able to use the bias trimmer without any change to other components.... However I would recommend you to add a least one more set of output divices if you entend to run it as a 300W amp
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Old 31st December 2003, 08:46 AM   #5
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Seems like a death wish to run transistors at or above their maximum voltage ratings. They do make MJE15032/33 and MJ21193/94, the outputs are about the same cost, the drivers a few pennies more.

SOA folds back above 50V on MJ15003/04
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Old 31st December 2003, 10:46 AM   #6
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Default transistors

thx

i could also use the mj15022 or mj15024.
they have 200v and 250v max. at 250w
is this right?

best regards
andreas
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Old 1st January 2004, 03:04 AM   #7
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The MJ15022/24 are a fine part and can handle 160W at 80V

The PL700 runs at over 100V.

SOA of the MJ15022/24 at 100V is only 100W, a MJ21194 has 200W SOA at 100V

The SOA of a MJ15003 at 50V is 250W, the big Crown amps are all bridged and use this type of transistor.
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Old 5th January 2004, 02:24 PM   #8
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Quote:
SOA folds back above 50V on MJ15003/04
What is folding back?

You've given a voltage but shouldn't you also give a current.

Does it foldback @ 1ma or 10a's?
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Old 5th January 2004, 05:16 PM   #9
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> what do you think on this amp schematic?

Very good for its time, over 25 years ago.

Buy LOTS of output devices. There should be twice as many in the amp. Also because it has no protection, you can fry the whole output stage and Q5 too. (Transistors always "protect" fuses.) Phase Linears were reliable in home use, but in commercial use were much less reliable than the Crowns.

The design is antique and it shows in the sound. Many of us who grew up on such amps like the PL sound. But the bootstrap ensures distortion at low level. This is largely masked by an obscene amount of overall feedback, but for stability the feedback is rolled-off inside the audio band and high frequency distortion tends to be high.

Still all in all, perhaps one of the best very-simple amps for this power level.
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Old 6th January 2004, 12:55 AM   #10
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"What is folding back?

You've given a voltage but shouldn't you also give a current.

Does it foldback @ 1ma or 10a's?"

SOA is a power. It is not a straight line. It will start to bend, ie: fold back, at some voltage.

A MJ15003 starts to foldback at 50V, a 2N6259 at 100V.

At 50V they are both 250W parts.

At 100V one is 100W, the other is still 250W.

A MJ21194 is 200W at 100V.
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