Fuse after the capacitors

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Guys .... need to find out first what is wrong and then think for a solution
You can buy a dual trace memory scope with at least 100 mhz response, and watch the base lines into the output transistors at turn on, to see if the problem is on the driver board or the output assembly. That is not a cheap solution, but it is a first step. You may have to inject a .5 ohm resistor into those lines to turn current into voltage, or something. Then the grounds of the two probes would not be common.
Two amps doing it same age suggests either 1. both have the same deteriorated part. or
2. bad design particularly in the bias split area.
 
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And how nec3 will expect the rail fuse to blow if its disconnected this morning ? Thanks for sharing a post but get some coffee first please .

I meant that,

assuming rail voltage feeds the whole circuitry, you could seperate the output power tranzistor bank to localize problem. From your post i see that "rail" voltage is used only for output tarnzistors. (?)

Thanks for coffe offer.
 
I got three 20 mhz scopes, i got one 40 mhz scope and one 100 mhz scope . Spectrum analyzer signal generators , function generators and another 30.000 worth of instrument Most important i also learned how to use them ...

Point of the thread is to find out if there is a known issue about these amps and learn a bit more about the specific issue which is the fuse after the capacitor .

In between 3 days playing the amplifier when cold or hot almost rapid switching on or off and so on and both amplifiers presented no failure , both of them

Since i dont have a schematic i think that Monday i will chart the time line and the boot sequence and then observe the behavior at start up in terms of current draw and base inspection .

Disassemble of the amplifier is a true pain in the *** even though the bottom cover gets removed with 6 screws so i will have to look the easiest way first .

Kind regards
Sakis
 
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More coffee Nec3 :p:D
its not the mains fuse blowing its the rail fuse that blows so removing the transistor block will not help anything
As about what powers what i guess a few things that i can measure and see but i dont have a schematic
yet again first stages are powered from a different supply and amplifier is hybrid so there is also a HV PSU involved

In general experience says that small signal circuits behind the the main output block are supplied from PSU that is not provided with current enough to blow a 15A fuse of a rail

Though as correctly pointed so far more than once at start up any flaw of the previous stages or start up sequence may drive the output to excessive current draw resulting a blown fuse .
 
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here is a question

For a number of reasons most manufacturers fuse before capacitor banks
Shows thoughtless design/implementation. The capacitors draw current at first start up. The fuse/s need to be selected to pass this start up current without rupturing in that first year of warranty. The fuse rating needs to be so high to survive this start up and warranty, that if a serious fault did develop then the oversized fuses would take tens of seconds and more probably many minutes to rupture. How much damage would that severely overheated amplifier cause during those many minutes?
For effective damage limitation to the surroundings, the mains fuse and any internal fuses should take account of start up conditions comensurate with rapid blowing. This requires the internal fuses to be after the main smoothing capacitor bank.
I come across one amplifier 6 output transistors per ch 40.000 uf per ch supplied with 50+50 volt Hybrid, trs output, trs drivers, tube first stage, and fused between output trs and capacitor bank ...

All fine but for no reason it seems that this amplifier may blow fuse in one rail
pop the hatch , replace the fuse and ready to go amplifier plays like hell biased according to the manual and seem to operate flawless

then again after few days blows a fuse and here we go again

Checked the basics almost everything appears to be fine, contacts,soldering , insulation , bridges and so on while the weird thing is that the amp is a monoblock so owner has another one that behaves exactly the same

Fused after the capacitors has anything to do with it ? Most of the times fuse issue takes place at powering up ....

Amplifier is Vincent SP-T100

Any ideas ?
if a F5A after the smoothing bank allows operation at full power all day long, do you need any bigger fuse?
Could that fuse be smaller and still allow 24/7 operations for days or even months? Would an F4A survive long term operation and start up?

Now relocate that fuse to before the smoothing bank. How big will it need to be to survive 365 startups from cold during it's first year of operation?
Will F10A do or F12A or even T12A.
How long will a T12A passing 15A survive?
How long will an F5A passing 15A survive?

BTW.
An F5A fuse supplying a 2pair output stage capable of instantaneous 40Apk would blow so quickly that the semiconductors will survive an output short accident.
Change to a T12A and that 2pair stage will almost certainly blow up on first output short incident.
 
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T15A or F15A secondary fuses?

How long will they pass big fault current?

BTW, a quick calculation shows that a pair of F15A, or T15A, fuses will allow continuous operation of 1500W into 2ohms. That is an almighty fuse rating !

Note it took me 8minutes to edit out all my typing mistakes !
 
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