DENON PMA 830 2SA815 Transistor Sub

[rjb5191]

Hi All,

I have a dead 2SA815 driver transistor in my Denon PMA 830 Power amp. I have some MJE172 and 182 that I'm hoping to use a sub or the 2SA815 and 2SA915. On paper they have good specs that exceed the original in many ways. Although they have a lower max Vce, they should be well within their limits in this circuit so I don't see a problem there. One area that is lacking in my knowledge is how different Vbeon and Vcesat specs will operate in this circuit. The MJE have about 20mV higher Vbeon and 5mV or so lower Vcesat readings on my Atlas DCA so I'm trying to determine if this will be an issue. The base voltages are pretty small in this circuit so I was concerned that a difference in those specs may make a difference.

Power amp schematic is attached

 

[ximikas]

Hi , what about compare speed characteristics of orginal and your replacement? If original was 15Mhz and replacement 3Mhz , it may oscillate , and increase distortion in high frequencies , so not best solution. Schematic looks very simple , so transistors spec's can have high impact. Different vbe voltage is not so critical, it may just change idle current, but you can adjust it by potentiometer.

 

[rjb5191]

Hi, thank you. MJE sub is 50 MHz so its significantly faster and also i have selected a few with about 20% higher gain than the original so I thought it would be good from this perspective. That's good to know regarding the Vbe.

 

[ximikas]

Use dim bulb tester for testing first.

 

[wg_ski]

For the 815 (driver duty) the MJEs will be fine. It would probably “work” for the 915. If you had any 2SA916’s (the giant TO-92) lying around I’d use them instead. Not sure if Fairchild is still making them.