Conrad Johnson ART amplifier fuse blown

[AnotherJohnson]

https://www.allfuses.com/ktk-2?gclid=EA ... gJdevD_BwE

These are by Bussmann. They are not cheap. Note they are rated for 600 V.

Change all your power tubes.

JF will tell you the same.

You dodged a bullet because the prior owner didn’t stick a 10 amp in there.

Get a couple of the KTK-2s.

Change your tubes. It’s time.

Enjoy the music.

[admin]

I took it as the description of fuse "F5".

ARTmanualFuse1.jpg

[AnotherJohnson]

Nope. That’s on the power input.
The plate fuses aren’t mentioned.

[admin]

Hmmm. Kind of odd that they don't mention the fuse that is designed for the home user to actually replace themselves (ie not having to open the unit up for replacement).

I tried giving CJ another call this afternoon. Left a message.

[AnotherJohnson]

They’re not discussed in the LP275M manual either. But there they are. Big as life.

Maybe the manual was written by Captain Obvious and he thought they were obvious.

[AnotherJohnson]

Note the fuses 1 - 4 are called internal fuses. The KTK-2s are definitely accessible without opening the case work.

[Big Dog RJ]

Yes, as AJ mentioned that's correct!

The owner's manual is correct as well. Such that it clearly states what those "internal" fuses are... that's why you have to open the bottom plate. They go on to mention that any of these fuses blown means a more serious problem and should be attended to by a qualified service tech...

That's basically clearly printed in every CJ manual, and the mains fuse, which Admin is referring to, is the one located near the IEC power inlet of the amplifier. These fuses protect the Input transformers and NOT the Output Transformers. They're completely two different types of fuses.

Those Bussman fuses are the ones, 600V or higher, you just have to get the exact one that is located in your amplifier, and CJ are the ones who know exactly which one, simply because they designed it!

Those big KTK fuses that protect the "output" transformer will only go off/blow whenever a bad output tube is encountered. It doesn't protect the AC mains input transformer. That's why CJ states when those internal fuses go/blow, it's a more serious problem... hence, a tube going bad is not so serious. Just throw out the bad tube and replace it with a new one!

Also, these much larger than life fuses are housed separately where the owner can easily replace them with the correct type only supplied by CJ. As I mentioned earlier, CJ used to provide two spare fuses of these in their owner's manual sleeves along with the bias wand many years ago but now they don't.

Also, as AJ rightly pointed out, which is an important point to note-

*if the owner replaces all output tubes during the average life cycle of the tubes (approx. 2000 - 3000hrs) then replacing those big KTK fuses would never require replacing! That may also be the reason why CJ doesn't supply them for free any longer. If you want those spares, you have to buy them separately.

OTOH, those are Bussman fuses and made in the USA or some made in the UK. I remember during my dealership yrs, we used to get an external supplier from Spore and HK. They were the same exact type and audiophile grade, not mickey mouse stuff. However, I don't have that contact any more but there are other suppliers who can supply audiophile grade fuses. Afterall, CJ only designs and makes the amplifiers but they also rely on external suppliers for such items. Therefore, if you manage to find out who, they will supply to you directly as well.

It's always good to have at least two spares of these large KTK fuses, in case you go through a few bad output tubes... However, as AJ said, if you replace your output tubes according to CJ's recommendations, these KTK fuses will last a lifetime!

Replacing all output tubes is the way to go, and the larger the amplifiers you have, the more tooobs you need and the costs goes up... things do get expensive but it's not every year, just once in 3yrs or so depending on usage. So it's fairly manageable provided you have the funds.

Things have gotten really slow... no one's answering our Aus importer either... we're waiting on the status for our orders as well. People are ringing asking when their gear should arrive, and their answer is- soon! But when? So I was told just today. Hopefully, they reply to you soon Admin and everything will be in order.

Cheers, RJ

[AnotherJohnson]

FWIW, RJ and I are on the exact same page. I constructed the note below before I saw his note, but I agree with him on all points.
********

The 10 amp fuse protects you and your house from an electrical fire. It blows around 1200 watts, so that’s a practical limit on the draw from the 15 to 20 amp circuit.

Those four internal fuses are protecting smaller components on the board. A runaway tube is the biggest threat to the amp. If the plate fuses weren’t there, the impending short could continue to draw until it broke to open, or the line fuse blew.

The plate fuse idea dates back a long ways. I know CJ was using them as early as the MV52 from personal experience. I expect that they go all the way back to the earliest CJ amps.

Not thinking in mm, I did not make the quick calculation that 5x20 is really .2”x.8”. Much smaller than a typical plate fuse which is always rated at a high voltage. Note that 2 amps at 600 Volts is watt equivalent to 10 amps at 120 Volts (the line fuse).

So … from the start I’ve been thinking that you blew a plate fuse, and assumed it must be covered in the manual. I did not look closely until Bobby posted the manual and I wondered why the KTK fuses weren’t mentioned.

I looked at my manual, and it was the same as yours. Yet there in my stores was a bag from CJ containing two KTK2s and hand labeled LP275M plate fuses.

Every time I get a new pre-owned tube amp, I check the plate fuses to make sure they’re correct. Since this is not covered in the manuals, and since my authoritative source is CJ (specifically JF), I now extract from memory conversations about this with CJ, and their sending me the spares per their specs.

[roberto]

If you read Aj, what he is saying is correct...RJ too.

Basically here in Costa Rica, because there are a lot of merchandise that comes from Europe, the fuses size are 5X20 mm. Then the 3AG size, these are the most common, comes from America. The 3AG size is 1/4 x 1 1/4 inches. The other types are rarely used. The Buss Fue, usually is a plate fuse BBS-1 on. most Cj power amps.

The MV-50 plate protection fuse is BBS type...

The plate fuse current usually is very small in current..this way the amp is protected for a heavy possible damage. When this fuse is open there is a bad power tube. In the power amp, usually a push pull topology circuit type, two or four tubes are used per channel. I was asking to Jeff, why not use a dedicated fuse for each power tube, and if it burns, we know which tube is bad. The excessive current draw by the bad tube will make this plate tube to burn...

Happy listening!

[admin]

Small update. So I had called CJ up twice and left a message, also emailed them twice. I gave them a call today and left another message on their VM. Funny enough, about 3 minutes after calling them, I get a response to my email that I had sent them 11 days ago. No joke. They must be really busy but folks waiting to hear back, have faith.

I had also asked them on what their recommendation on replacing one tube at a time vs all 16. They advised that if the unit has 2,000 hours on it, they recommend doing all 16. Otherwise, just the tube that went bad.

Funny though, they didn't quote me any price on the fuse or the tubes! So I replied with requesting the amount. I'll keep you guys updated. The amp is running fine for now and I'm loving the the tunes with my new DAC and streamer setup.

[AnotherJohnson]

Small update. So I had called CJ up twice and left a message, also emailed them twice. I gave them a call today and left another message on their VM. Funny enough, about 3 minutes after calling them, I get a response to my email that I had sent them 11 days ago. No joke. They must be really busy but folks waiting to hear back, have faith.

I had also asked them on what their recommendation on replacing one tube at a time vs all 16. They advised that if the unit has 2,000 hours on it, they recommend doing all 16. Otherwise, just the tube that went bad.

Funny though, they didn't quote me any price on the fuse or the tubes! So I replied with requesting the amount. I'll keep you guys updated. The amp is running fine for now and I'm loving the the tunes with my new DAC and streamer setup.

That’s pretty much what we said about the replacement strategy.

Regarding the price, “If you have to ask, you can’t afford it.”

In my experience, the CJ price will be high. But you do want them to stay in business, right? So they have to make a bit of money, especially in support of used older products. We’ve already gone round the barn on other suppliers.