UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Sony-STR3800L. Output transistors.

samjmann · 30th Jan 2023, 12:17 am

Update after fitting! After replacement of both output transistors all was well. Well at least for a while...

The set up went ok, both channels had much the same quiescent conditions. However a week later after switching on, the same two transistors went short again. Clearly something was wrong. I'd checked the bias diode D701/D751 and it read ok. I was having to now put the bias pot at near short circuit to stop the 2nd replacement set of output transistors failing. The SV04 bias diode now reads O/C but only when the leads are moved. Its mounted on a tag that's attached to the top output transistor.

The SV04 is a 4 diode package, the good one reads 2.3v on my meter
Does anyone know of a suitable replacement?

I could make up substitute with a 4 diode string. I'm not to sure what the current would be in the diode string, hence what would make a good substitute.

Regards SJM

30th Jan 2023, 12:17 am	#10
samjmann Heptode Join Date: Feb 2014 Location: Nottingham, UK. Posts: 648	Re: Sony-STR3800L. Output transistors. Update after fitting! After replacement of both output transistors all was well. Well at least for a while... The set up went ok, both channels had much the same quiescent conditions. However a week later after switching on, the same two transistors went short again. Clearly something was wrong. I'd checked the bias diode D701/D751 and it read ok. I was having to now put the bias pot at near short circuit to stop the 2nd replacement set of output transistors failing. The SV04 bias diode now reads O/C but only when the leads are moved. Its mounted on a tag that's attached to the top output transistor. The SV04 is a 4 diode package, the good one reads 2.3v on my meter Does anyone know of a suitable replacement? I could make up substitute with a 4 diode string. I'm not to sure what the current would be in the diode string, hence what would make a good substitute. Regards SJM Attached Thumbnails __________________ It's never been right since we've had it...