Hi,
I have an old Arcam Alpha 6 plus amplifier which uses 37v-0v-37v voltage configuration. The amp works fine.
However, occasionally the fuse blows when I switch on the amp. I believe this is due to insurge current. When I connect the amp thru a current limiter (330w halogen light bulb), the fuse does not blow at all even after months of usage.
How do I prevent the insurge current? I heard you can use a thermistor? But what type? Where should I install this thermistor?
[Updated: Solution found: see the last post]
Thanks,
Dino
I have an old Arcam Alpha 6 plus amplifier which uses 37v-0v-37v voltage configuration. The amp works fine.
However, occasionally the fuse blows when I switch on the amp. I believe this is due to insurge current. When I connect the amp thru a current limiter (330w halogen light bulb), the fuse does not blow at all even after months of usage.
How do I prevent the insurge current? I heard you can use a thermistor? But what type? Where should I install this thermistor?
[Updated: Solution found: see the last post]
Thanks,
Dino
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Use a time delay or anti surge fuse of the correct value.
230v 800mA T and for 120v 1A6 T are the correct fuses.
230v 800mA T and for 120v 1A6 T are the correct fuses.
Quite hard to find 1.25A delay fuse with the right length. I'm using normal fuse. Any other option?
Its 1.25A @ 250v which give rise to around 300watts. I have tried 2A fuse, which does not blow, but the power transistors burnt instead and its full short circuit where the 2A fuse also blows. However, when I limit the current via light bulb approach amp plays beautifully thru my Kef (6 ohms) or Mission speakers (8 ohms). I dare not try it on my ELAC Unifi FS U5 floorstanders at 4 ohms in fear it might blow these brand new floorstanders
The fuse is located in the main input line inside the Amp where the power sockets connect.
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I doubt it is the fuse... replaced it many times... but using normal fast burn fuse which is easily bought n cheap.
Back to my question, should I use a Thermistor and where should I use it? Which kind?
I've attached the power supply schematic for this amplifier. Clearly it shows using delayed spring loaded fuse.
Attachments
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The schematic clearly shows 1Amp for 230v and 2Amp for 120v Both are Slow Blow or Time Delay type.
Why not repair the cause; problem solved then.
Either values are common in both 1 1/4" and 20mm sizes.
Even 1A25 is available in both sizes; Cartridge Fuses | RS Components
Why not repair the cause; problem solved then.
Either values are common in both 1 1/4" and 20mm sizes.
Even 1A25 is available in both sizes; Cartridge Fuses | RS Components
Yes, NTC can help. You can put NTC in Phase Line (L) or in Neutral Line (N) (where there is a free space). Nominal can be about 5 Ohms (or little more), diameter 9-11-15 mm.
Starting point for estimating resistanse of NTC-termistor is active resistance of power transformer primary winding - NTC nominal may be about the same (depends of...)
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Would these NTCs be ok? It is rated at 6A and 4.2A, however, the amp only uses 1.25A at the primary winding of the transformer. Or should I just get the thermistor with 2A nominal current at 240v?
1. https://my.element14.com/epcos/b572...c-ntc-5-ohm-20/dp/2101626?st=5 ohm thermistor
2. https://my.element14.com/epcos/b57235s0509m000/thermistor-ntc/dp/9751866
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I managed to find the slo blo fuse for 1.25A at Element14.com. However, it is expensive for just a fuse, and I still thinking of putting a Thermistor to manage the insurge current.
This points to some severe issue within the circuitry, as susbtituting a mains fuse with another of higher current capability mustn't affect the amplifier itself.
Best regards!
Alright I will try the 4.2A as the fuse is only rated 1.25A @ 240 volts. Hence should be within the limit of the thermistor.
I think you should monitor the NTC temperature (very carefull, it's dangerous, switch off it from wall socket), and find 1 A fuse.
9.5 mm NTC will be hotter then 15 mm, and will have smaller resistance after several seconds-minutes.
And what is your power transformer primary winding resistance?
9.5 mm NTC will be hotter then 15 mm, and will have smaller resistance after several seconds-minutes.
And what is your power transformer primary winding resistance?
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https://my.element14.com/bel-fuse/5st-1-25-r/cartridge-fuse-time-delay-1-25a/dp/2844497?st=20mm fuse
These ones are only 0.44USD each and have a MoQ of 1.. so not that expensive really.
Or treat yourself and get 25 for about $6USD:
https://my.element14.com/multicomp/mc000882/fuse-cartridge-1-25a-time-delay/dp/2461213?st=20mm fuse
But why is there an inrush current now? Surely the amp has not always exhibited this behaviour from new?
If your fuse keeps blowing, then there is something wrong. Always. Yes you can soften the inrush with a thermistor but really that only masks a problem which may only get worse over time.
You mention that if you use a too-high rated fuse your output transistors burn. As Kay pointed out, there must be something wrong with your amp because a properly functioning 'healthy' amp would not burn up if you were to bridge the fuses.
Have you modified the amp or replaced anything that could contribute? Installed decoupling caps on the output transistors perhaps?
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