Sony TA N7B Vfet versterker

[buisje]

No 2sa1220a 2sc2690a are the 2 driver transistors on pre amp board.

Those onsemi D450 D44 are on final stage/heatsink, but read it all over it is 10 years ago for me..

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Verder een goede kwaliteit weerstand kiezen voor de tegenkoppel weerstand.[/quote]
Do you mean R213, R113 4.7K?

Anybody noticed a mistakes in service manual on silkscreen and components list (R153, R253)? I think the last should prevail.

Are there a Japanese made output BJT replacements?

[buisje]

yes i chose allen bradley 5K resistors

[buisje]

And D44/45 BJT is for the output amplifier on sink very suitable,

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Do you know where to find 4R7 R127, R227? I can't locate them in the amplifier. Seems like they should be connected from GND to amplifier chassis. Perhaps they were omitted by Sony.

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I powered on the amp without VFET installed. Measured DC Bias voltage are 5mv \ 1.8mv on every channel. Should I set DC Bias to 50-60mV without VFET installed or it will raise itself when I put VFET in?
Also heatsinks of driver pair (c1663\A835) of left channel are little warm (collector voltage on C1663 is 5-6V higher - 65VDC than on other transistors of every channel) while on other channel (collectors volatges are 58-59V) these heatsinks are quite hot. Is it normal or perhaps one pair of drivers are overloaded?
Btw, I still haven't changed output bjts to D44 \ D45, bought some fakes recently. Will use 8 Ohm speakers than.
Cannot attach the picture, HTTP error appear.

[buisje]

have ot checked schematic for the 4r7 resistors.

best is to set bias pot in middle and power up, and quickly check and adjust bias current and offset.

Without end transistors the drive transistors get hot indeed. I urgent suggest to replace those D44 and 45 power transistors, the original ones are more likely to get faulty and pull with them those nice Vfets in their grave yard/tomb ...

[buisje]

So get those transistors from a respected supplier, these days a lot of china remake is coming up too often

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DC offset is fine even without VFET, 0-5mV. Do you recommend to set the bias with VFETs inside only?

I set the bias equally to 4.5mV on both channels and the drivers are on the same temperature, little hot.

If I leave the DC bias as is (it were original setting) and put VFETs in, won't they get damaged with such setting?
Setting the bias to minimum 30mV without VFET will fry the drivers for sure. I'm afraid I can't quickly set the bias to correct values if I set the pots in the middle position. With such bias measure points I have to measure than to adjust and the same again. Than the same with other channel. I think it might take at least 5min or so.

Will have to order D44\45 from abroad.
If my current old capacitors 1000uF63V are still good, measuring better then new Nichicon PW I bought, should I replace them than?

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I found those resistors, they are between main ps capacitors.
Should I change ceramic capacitors to silver mica ones? Maybe tantalum capacitors should be changed as well, as I know, they are prone to failure