NEED 2SK225 & 2SJ81 FETs for Sugden amp! Help!
I NEED 2SK225 & 2SJ81 FETs for a recently dead channel in my dear old Sugden A25 amp-
These old Hitachi FETs are obsolete- and I cannot find a cross to them.
Can anyone offer a suggestion of a replacement pair?
And, if I replace the dead channel's pair, do I also need to replace the other channel's FETs to keep both left and right sounding the same?
I NEED 2SK225 & 2SJ81 FETs for a recently dead channel in my dear old Sugden A25 amp-
These old Hitachi FETs are obsolete- and I cannot find a cross to them.
Can anyone offer a suggestion of a replacement pair?
And, if I replace the dead channel's pair, do I also need to replace the other channel's FETs to keep both left and right sounding the same?
Hi, Can you first of all confirm what package they are. T03, or flat pack. By the way, have you tried E-Mailing Sugden to ask what they recommend. They are a very friendly bunch, and I had the good fortune of a tour of the factory a couple of years back. Worth a try ? Back to the FET's, there was a similar thread a while back and I made the mistake of assuming the 2SJ/K type were like the laterals we know today, when in fact they are not. Some of the very early FETS have very different transconductance characteristics and the pinch off voltage is significantly different, they are not directly equivalent with the modern types.
Regards Karl
Regards Karl
I need some help to resolve a problem with the two transistor on the 18v supply (BC639/BC640) They run very hot and finish to burn. I have 30v on the base and collector and 19v on the emitter on both. Should I check the current consumption that goes through the 18v supply to see if it does not overload the BC639/BC640?
30V on bases and 19v on emitters is definitely not right, no surprise they're burning up.
If you can refer to the schematic in post #8 look at the T6 and T7, if you can explain me why it's not right would be greatly appreciated. I have tested all the resistors and diodes related to those transistors and all tested fine.
T6 & T7 form a pair of regulators.
clip your black DMM lead to Power Ground or to PSU Zero Volts.
Use the Red lead to measure voltages referred to that Zero Volts.
BC639 E:+19.50v C:+31.50v B:+20.25v
BC640 E:-19.25v C:-31.00v B:-19.75v
OP2 is a NE5534 with 100% feedback at high frequencies. This chip is not unity gain stable, so may be oscillating. Should have a compensation capacitor.
Power consumption off the +/-18V rails should be about 15mA, which implies ~200mW power dissipation, fairly hot to the touch
Power consumption off the +/-18V rails should be about 15mA, which implies ~200mW power dissipation, fairly hot to the touch
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