HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Can anyone give me advice on how to change the fuse on my Unison Research smart 845 monoblock power amp please. Or point me in the direction of someone able to repair such a beast. Many thanks.

I found a thread on DIY Audio (USA forum) but you might not be able to read it if you are not a member.

https://www.diyaudio.com/forums/tubes-v ... y-goo.html

A Mr John Caswell (near Reading UK from memory) might be able to help you (he posted in the thread) but I know for a fact he is not accepting any jobs during the Covid 19 pandemic.

Nick Gorham (member here Lurcher 300b) might be able to help, he's the ace man for the job and being in West Yorkshire is nearer to you.

Hope that helps.

Which fuse? I assume its internal.

The first question you need to answer before changing a fuse is why did it blow.

Lurcher300b wrote: ↑Fri Apr 03, 2020 10:58 am Which fuse? I assume its internal.

The first question you need to answer before changing a fuse is why did it blow.

Absolutely!

Whilst it is not unknown for fuses to fail due to oxidisation I doubt this amp is old enough for that and It is easy to blow amplifier fuses with a sustained sine wave but I doubt the OP would have done that either. I certainly wouldn't just replace the fuse and carry on. My experience with valves is near non-existent and I wouldn't even start without the circuit diagram.

Lurcher300b wrote: ↑Fri Apr 03, 2020 10:58 am Which fuse? I assume its internal.

The first question you need to answer before changing a fuse is why did it blow.

Hi Nick. It is the fuses in the drawer at the back. I have ordered some from Amazon. I swapped the ones from the other channel and it powers up fine. So I still have one channel down at the moment.

Thanks for the help guys.

Ok, so its the 20mm fuse in the IEC (probably slow blow). Sounds like you have fixed it. Worry if it keeps doing it.Is the amp got a valve rectifier? They can sometimes arc as they get old and that will take a mains fuse out.