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Added-On Bandmaster Fuse Blows

12/10/1997 12:27 PM
Added-On Bandmaster Fuse Blows
In accordance with Torres' amp book, I put in a 160ma fuse to protect the output transformer's center tap (red wire). Everything was fine for a few months. But now that fuse blows frequently (but not every time) when I engage the standby switch after warming up. If I leave the standby switch in the on-position when I turn the amp on, everything is fine. Should I increase the fuse rating or is something else amiss? Or do I even need this particular protection scheme? Thanks in advance for your input.
12/10/1997 12:53 PM
J Fletcher
Well,when that amp is running at full power it's drawing around 200ma,and I would guess when you first flip the standby there is a surge that could exceed that.I think you probably need about a 500ma slo blo fuse,160 ma seems low to me.
12/10/1997 1:29 PM
I didn't know the output transformer drew that much current. Would a 250ma fast blow fuse be suitable, as well as your recommendation of a 500ma slow blow? I wonder why Torres specified a 160ma?
12/10/1997 2:16 PM
J Fletcher
If you put a 250ma in series with a 500ma slo blo,the 250ma fuse will always blow first,so the 500ma fuse would be redundant.I think 250ma is too small,and you'd be better off with a slo blo.Of course this is coming from someone who doesn't fuse the high voltage in his own amps.However,I looked at a Marshall 50 watt JCM last week,and the high voltage windings were fused with 500ma slo blo fuses.After all you're fuses shouldn't be the cause of problems,they should be insurance against small problems turning into large ones.
12/10/1997 7:41 PM
>> I wonder why Torres specified a 160ma? <<  
One possible thing to consider is that Torres biases his amps like ice. Maybe he gets away with it because of that.
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