23-04-2012, 11:34 AM
I was using PP9s when I blew those transistors. I wasn't sure if my PSU may be the cause of the trouble and it can only manage an output of about 15V.
I've re-examined the corpses and found T3 (which is an AC127) and T5 are short circuit and T4 open.
I can get the quiescent current down to 12mA and it work at low to moderate volume with things cool. Turning it (the volume) up higher caused a machine-gun type noise (motor-boating?) which the ammeter needle spikes up in time with it.
I was dong this with it connected to the PSU which was delivering 15.45V. When I switched to batteries it didn't work.
So it looks like progress is being made but there's a way to go yet. It seems like a stability thing and I am wondering if there'd be any point in changing T2 so that all four would be silicon ones.
As to what was initially wrong, it seemed blooming loud. To listen to it the volume knob only needed to be just clicked on which is what lead me to think that there was something set wrong which was causing over-loading.
- Joe
I've re-examined the corpses and found T3 (which is an AC127) and T5 are short circuit and T4 open.
I can get the quiescent current down to 12mA and it work at low to moderate volume with things cool. Turning it (the volume) up higher caused a machine-gun type noise (motor-boating?) which the ammeter needle spikes up in time with it.
I was dong this with it connected to the PSU which was delivering 15.45V. When I switched to batteries it didn't work.
So it looks like progress is being made but there's a way to go yet. It seems like a stability thing and I am wondering if there'd be any point in changing T2 so that all four would be silicon ones.
As to what was initially wrong, it seemed blooming loud. To listen to it the volume knob only needed to be just clicked on which is what lead me to think that there was something set wrong which was causing over-loading.
- Joe
