If it's knocking out a 6.3 amp fuse, and the correct rating that it's expecting to have in there is a 7 anyway, then trust me, it will have no problem taking out an 8. I wouldn't necessarily say the same about a 10A, but the extra couple of microseconds to blow an 8 is not going to damage anything else. Have we actually established if you have the proper " T " rated type in there yet, anyway ? If you haven't, then all of this conjecture about what *might* be wrong is a useless waste of time, as there may be nothing at all wrong other than an invalid fuse type for that application ...
I have no idea what type of fuse i'm using. There is no making on it saying it's a "T" I checked the web site of the company that makes the fuses and i don't see any "T" listed for that fuse. It's 250V 6.3A GFE Miniature fuse made by Conquer.
I'm gonna take a strol over to the repair shop and see if they have any 250V 7A or 8A "T" fuses.
I've looked at Radio Shack or The Source up here in Canada the only 7A fuses they had were 1-1/4 X 1/4 it didn't look like they would fit into the fuse holder.
I was thinking maybe, could i replace the fuse holder with a breaker? I noticed the the manual they talk about a breaker switch and not a fuse or fuse block.
Ok i see i'm using a GFE type fuse when i should be using a GDC type fuse i was gonna ask how to tell the difference. I almost missed that line above my quote.
So i guess a GFE fuse is just an ordinary run of the mill every day fuse And a GDC would be a slow blow.
Now are Time Delayed and Slow Blow fuses the same thing or are they different.
Man you know how much this would cost me if i was to take a course and my local collage to find this stuff out:):):):):)
I think we narrowed it down to me having to use the proper fuse. Which obviously i am not using in the amp
I'm surprised this didn't happen along time ago. Maybe because of the new part that was installed.
On further inspection of this amp i noticed the Output Transistors are as follows
2- c2837's as a pair
2- a1186's as a pair
1-a1492 \__ shouldn't these be the same
1-a1186 /
1-c2837 \__ shouldn't these be the same
1-c3856 /
I was just wondering it's probably the design of the amp. Kind of through me when i took a closer look I would have thought that each of the last 2 pairs would have been matching like the first 2 pairs.
Shouldn't the 1 side of the amp be a mirror of the other side. Or is this because you can switch it to Bridged mono?
Just let me know if you guys are getting tired of all these questions:).....My head is like a sponge now. The more i learn the more i want to learn.
i uploaded a schematic onto abse it's in Microsoft Office .rtf form i had to convert it from PDF to be able to print it properly
They are in principle the same thing but a US 'slo-blo' and a European/International 'T' have slightly different fusing characteristics. Not different enough to worry about in this case though.
LOTS !
What type was it before that part failed though ? It was probably originally the right type.
The fuse that went when all this trouble started was the same type that i'm replacing 250V 6.3A No "T" type or slow blow. I never had a fuse go until i had the problem with the output.
I'm about to turn the amp on right now and see what happens. I'm gonna check and see if i can get the 7A slow blow fuse from the repair shop I checked radio shack and they didn't have them in the mini fuses
It would seem that your transistors have been subbed when it was repaired. This is not uncommon, and I have on occasion done it myself, although where possible, I prefer to use original types, even down to actually obtaining them from the equipment manufacturer, rather than a third party general spares supplier.
Theoretically, the transistors should indeed match on both channels, as your schematic suggests. Sometimes however, particular types are either difficult to obtain, or prohibitively expensive. Most repair people will have their own favourite substitute types to use in cases like this. Usually, these substitute parts are chosen to be better rated than the types that they are replacing, so don't cause a problem. In general, the output transistors are just meaty current carriers, and for the most part, due to the large amounts of feedback being employed, and automatic bias stabilisation, their exact characteristics are not that important. Occasionally though, an output circuit design is critical of such parameters as transistor gain, and substitute devices just will not work well in it. This usually manifests itself, however, as symptoms like long-term overheating, and a failure of the bias circuit to operate correctly. Also, some output stages use darlington transistors, which of course cannot be substituted with 'normal' types, and in fact I would not recommend that they be replaced with anything other than originals.
Without going and looking up the differences between what was originally fitted, and what is now, I wouldn't like to say for sure whether they are valid substitute types, but I'm willing to bet that they will probably be OK, and are not the cause of the problem, as you said previously that when it is running, it does not overheat, and sounds fine.
Fuse blowing at switch on is not something that you would normally consider to be output stage related, unless it is a 'hard' fault such as a short circuit device, in which case, the amp would never be able to work. I still think that all you need, is to get the correct fuse type in there, and all will be well. If the type that is in there is indeed a fast blow, as Graham's research would suggest, then it is not a valid type for that position, and will blow in just the way that you are seeing. Also, as Graham says, slo-blo and " T " rated are not quite the same on paper, but to all intents and purposes for this discussion, they can both be treated as 'equivalent' anti-surge types. Get the right fuse in there, and then come back to us in a couple of weeks and tell us that it's OK now.
Agreed possible. Would depend on how quickly the fuse blows after the on / off switch is made. I would expect there to be a short delay before a hooting output built up enough oomph to draw the current necessary to blow a
6 odd amp primary fuse. I got the impression that this fuse was going out pretty much immediately that the switch was closed, and also without any signs of distress, which would indicate to me that it was breaking just through metal fatigue from repeated inrush-surge sagging events. A hooting output stage would blow it as a result of pulling excess current, which at the high frequency the instability would be occuring at, the tranny's inductance would probably try to limit anyway. A fuse which has blown as a result of an excess downstream current, usually shows as having a melted middle, with blobs on the ends of the broken wire. I reckon that it will all be ok with the proper fuse in it.
I think you nailed it on the head. It did seem strange to see the different output trans in there. I'm thinking that because if that whoever owned the amp before me must have had it in for repair. Or it might have even come from the factory that way. Due to shortage of parts.
I'm going to grab the "Proper" fuses for the amp and see how they work. Right now i believe that is the only problem with the amp.
It's always better to get different points of views. Especially from people that have more experience in this stuff than me.
Having said that, it's kinda like a blessing in disguise. Cause after reading all i can read about it and all this info i've been getting i really want to get into the electronic repair more. I'm gonna sign up for some courses and the collage and get into this. I find really fascinating a shit if something goes wrong i'm the type of person that would rather fix it myself.
I did that with cars, construction, computers why not take the next step and get into electronics. I have to admit some of the stuff is a little over my head. But i'm understanding so much more now. It's so cool
Thanks for the help guys, you've put my mind at ease and i know where to come for help in the future
My old apprentice mentor many many years back, told me that the only way you should be able to tell that a component has been replaced, is if the soldering is *better* than the manufacturers original ! A good maxim I think, and one that has stuck by me for my whole life in the business. I never use too little solder on a joint, nor too much, and always clean off the flux residue.
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