NAD310 Repair, BUK555-60B Alt, IRL540N?

[TaylorD93]

Hi Everyone,

I recently picked up a NAD310 Amplifier from ebay, it was spares repair and after finding the service manual online i set about fault finding. Luckily the circuit is really easy to fault find and i traced the issue to the Output stage, bit of an odd layout (to me anyway) where the "high" side of the Class AB output is a MOSFET while the "low" side is a BJT Device.

Anyway, the MOSFET has failed, it is a BUK555-60B, this seems to be discontinued now, so other than a Used device or a possible counterfeit device, id rather find a modern replacement i can buy from a reputable seller in the UK.

Im not so great with MOSFET Datasheets, alot of figures im not sure of the significance of, but i am looking at the IRL540N as an alternative, similar Vgs of 1-2VDC and Power rating. Also a similar minimum Transconductance

The IRL540N does have a higher VDS rating (100V instead of 60V) and a slightly higher RDS at 0.11 Max, but as its in a Linear/Amplifier output stage, i would presume that the RDS is not so critical as it is not being used in a switching circuit. the 540N does also have a slightly higher Input capacitance, but again as its a Audio amp, does 2200pF (IRL540N) vs 1450pF (BUK555-60B) really matter?

Could these changes cause oscillation of the amplifier? or is it worth just trying it out anyway?

I have a 8 Ohm resistive load i can test the amp with first before actually running it with a set of speakers, but i rather avoid any further damage to the amp because of my component selection.

Any thoughts or guidance would be greatly appreciated

Thank you, Taylor

[David_AVD]

You can buy the correct part here: https://www.utsource.net/sch/buk555-60b.html

I've used them a few times and not had any issues.