Amp blowing fuses

If BAT is doing the upgrade at no cost for original owners, then I think they have it covered. Do not know that they are, though. If I was an original owner I would certainly be telling them that I expected the fix for nothing.

Hmmm.... BAT tells you that earlier models "need" an upgrade and that it costs $500. That sounds like BAT put out a bunch of under-designed, defective products, realized what they did wrong later and now want to charge people $500 to correct their mistakes. Not good and doesn't say much for BAT. Sean
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BAT told me that the VK-200 needs an upgrade to the bias circuit, at $500, which might be your problem. I know that S/N 274 and earlier need the upgrade and S/N 371 and later do not. I am not sure where between these two S/Ns BAT made the modification to the bias circuit, but yours may be one of the older models which needs the work.

Sometimes a bad tube can also blow a fuse. I had an amp that was working fine until it blow the fuse one day. I replaced the fuse and I saw the rectifier tube was very unstable and it blow the fuse again. I replaced the retifier tube and problem still exist. I then trace the circuit until I found out that one of the output tubes had a short. You never know...

Just because you've got a cap in series with the circuit does not mean that you are guaranteed to be "DC free". Sean
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The reason the fuses are there is to protect the unit from stuff like you just experienced. If the fuses do not continue to blow with a different set of interconnects, you have your solution. If something is wrong with the unit, it would blow the fuse everytime you turned it on. Otherwise, it's an external problem. When an interconnect grounds as yours did, it will pop fuses because of the high input surge to the amp and the subsequent peak out.

Sidssp,
does it?

Sometimes fuses blow for no apparent reason. Maybe it was just a weak fuse. If you replaced the fuse with the same type and all is now well, I wouldn't worry about it. If it does it again then I would do as Jafox advised. I fail to see the logic in blaming the preamp and demanding a replacement because the amp blew a fuse.

DC? I thought VK-31SE uses capacitor coupling at output. There is no way DC can get out unless the caps are damaged but I doubt this is the case since the BAT is pretty much brand new.

Hold on here Marakanetz.........not so fast! He said the problem went away when he switched interconnects. Did the fuse blowing problem return when the questionable interconnects were put back? Did the other channel of the amp or other mono amp fuse die when you swapped interconnects? Before we race to blame the preamp, there are a lot of other things to check. If the problem is stil there, try swapping tubes between the 31SE's channels. I have a ton of tubes in my system and they go as do fuses from time to time. But I do not just rush to box up a unit without troubleshooting with cable swaps, tube swapping, trying cheater plugs, unplugging other components, etc.

And by the way, I got the 31SE last year and it is wonderful. It pairs beautifully with the Aesthetix IO and Manley DAC as sources.

So let us know if you find anything. It could be the 31SE but it could save you a ton of time to try these other things first.

John

It's DC at VK31's output.
I'd suggest to replace the preamp untill it's on warranty.