Technics SU-8080 pre-driver qstn

[slimecity]

Hi there - I have a technics SU-8080 - lovely amp - with a blown 2SC1913(R) pre-driver transistor. Main Outputs test OK. Looks like I'll need to replace all 4 x 2SC1913 and 2SA913(R) pre-drivers (1 of each in each channel).

These appear to be replaceable with generic MJE15030G & MJE15031 transistors. However - any potential issues with this amplifiers' circuit re: stability if I use these transistors, and use them with the original outputs? (Im quite looking forward to using them, if I can.....) cheers!

 

[ryuuoh]

As long as the important specs (voltage, current, gain) are comparable it should be fine. Watch the pin out, it might be different on the replacements.

 

[slimecity]

OK, this is interesting. I finished doing replacement work and modding this amp. Total recap, some silmics used, some zeners replaced, dodgy relay driver transistor replaced, etc etc. Then I went to replace the 2SA913s and the 2SC1913s with MJE15030G & MJE15031 transistors. The pinouts to the latter are the same. Once done, the relay wouldn't engage - I tested the DC offset on the "before" side of the relay and that read OK, as did all the other readings. I replaced the original transistors (they weren't blown after all) and - the relay engaged, all good. I would prefer to use the MJE15030G & MJE15031 transistors if possible - any thoughts as to why using these MJE's would cause the protect circuit to see an issue? Im aware of other users of this site making this exact same sub without any issues.....?????

 

[slimecity]

Hi Inductor - by quiescent do you mean bias? Yes that was also fine - I had re-calibrated the amp earlier and the values hadn't drifted. Altho i had just turned the amplifier and the bias on these amps adjusts with feedback on heatsink temperature etc etc, so perhaps the amp just needed time to warm up a bit? Bias testing at cold was within limits but of course thats a bit meaningless as the amplifier hadn't warmed up.