I acquired a B&K ST-140 and I'm looking for some help with modifications to the power supply. I'm not really experienced but willing to learn from any existing material or circuits.
Incidentally, when I got it, one channel was distorted. A guy familiar with this amp told me it was likely one of the rail fuses. I checked and there is one blown. I want to replace it... I know it's 4 A but how do I recognize if it's fast blow or slow blow?
Mike
Incidentally, when I got it, one channel was distorted. A guy familiar with this amp told me it was likely one of the rail fuses. I checked and there is one blown. I want to replace it... I know it's 4 A but how do I recognize if it's fast blow or slow blow?
Mike
Welcome to diyAudio Mike 🙂
Look for any letters on the fuse caps. An anti surge or slow blow will say something like T4A or AT4A while fast will say F4A.
There may well be an underlying cause for the failure unless it is a known issue and random failure occurs for no obvious reason. Make sure to remove all power and wait a few minutes for any capacitors to discharge before replacing it.
Good luck.
Look for any letters on the fuse caps. An anti surge or slow blow will say something like T4A or AT4A while fast will say F4A.
There may well be an underlying cause for the failure unless it is a known issue and random failure occurs for no obvious reason. Make sure to remove all power and wait a few minutes for any capacitors to discharge before replacing it.
Good luck.
It might even be marked on the PCB under or next to the fuse. The fuse itself should be marked though.
They are marked 4A F so I presume fast blow. I want to replace them with audiophile grade fuses... I know that's probably woo woo on this forum, but my question comes down to this: the shop is out of 4 A fast-blow fuses of the large size... how bad would it be to substitute 5 A fuses?
Thanks for all your help.
Thanks for all your help.
Yes, that's a 4 A Fast fuse.
Fuses are safety components and so I can't in good conscience say that a 5A is OK.
Given that it is a fast type suggests it could be either a speaker feed fuse or a rail supply fuse.
I'm going to say try a 3.15AF instead and at least confirm the amp is otherwise OK. Fuses are simply a piece of thin wire that heats up the more current flows until such time when the fuse current value is exceeded, the wire then melts and breaks the circuit. There really is no such thing as an audiophile fuse beyond the wrapper and price tag 🙂
A good test with a faulty amp is to power it up with a DBT (dim bulb tester) to ensure all seems OK. The bulb limits any fault current and simply lights if a high current is drawn.
Fuses are safety components and so I can't in good conscience say that a 5A is OK.
Given that it is a fast type suggests it could be either a speaker feed fuse or a rail supply fuse.
I'm going to say try a 3.15AF instead and at least confirm the amp is otherwise OK. Fuses are simply a piece of thin wire that heats up the more current flows until such time when the fuse current value is exceeded, the wire then melts and breaks the circuit. There really is no such thing as an audiophile fuse beyond the wrapper and price tag 🙂
A good test with a faulty amp is to power it up with a DBT (dim bulb tester) to ensure all seems OK. The bulb limits any fault current and simply lights if a high current is drawn.