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Old 27th March 2013, 08:04 AM   #1
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Default Unknown mosfet amplifier

Hello
I have this amplifier ( which given from my Frend ) , this is mosfet 2sj49/2sk134 amplifier , and driver transistor is 3 pair of bf469/bf470. I have serach over net and dont find anything of this amp. This amp build somewhere of 1980-1990 years in Germany. Amp is very good but i wont build another pcb and , put new capacitors and elektroliytes , resistor and put new transistor ( bf469/470 replace with ksc3503 and ksa1381).
Anyone have schematic or something.
Thank You
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Old 27th March 2013, 10:55 AM   #2
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It looks very likely that it is a DIY variation of the original Hitachi MOSFET amp developed in the late 70's. If You search the web for that , you will find a zillion schematics dealing with that kind of circuit. The one on the attached schematic is one of them, but I am sure it is close to what you have there.
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Old 27th March 2013, 11:05 AM   #3
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Two Lateral MOSFET output pairs drive by 3 pairs driver?
I think driver by 1 pair and 2 are Vas.
Or, very like Goldmund, one pair power output drive by one pair driver, like this:
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Old 27th March 2013, 11:08 AM   #4
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I have search but i dont find , scheme like Your ( dragonweed ) post i know but identical schematic of amplifier i cant find.
This not schematic of my amplifier , i look on cresendo, axl and many oder circuit diagram and cant find right one.
Thanks
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Old 27th March 2013, 11:12 AM   #5
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VAS is 2 piece bc556b,
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Old 27th March 2013, 12:30 PM   #6
bluevas is offline bluevas  Indonesia
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Please inform us the transistors type and the value resistor
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Old 27th March 2013, 01:09 PM   #7
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when i picture all pcb and componetnts i will post here
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Old 27th March 2013, 01:32 PM   #8
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looks like Elector Crescendo amp?
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Old 27th March 2013, 05:06 PM   #9
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no
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Old 27th March 2013, 05:36 PM   #10
srh is offline srh  New Zealand
Mmm, FETS
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Hi, The amplifier is the ETI Series 5000 using ETI 477 modules. Designed by David Tillbrook and published in ETI Australia in the early 1980s. Quite a popular design here in Australasia.
100 Watts into 8 Ohms. It is based on the Hitachi app note, the major difference being the VAS consists of two cascaded differential pairs (BF469/470) ala Otala. Source resistors should be metal film types to avoid parasitic oscillations.
Regards,
Steve.
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