Conrad Johnson ART amplifier fuse blown

[admin]

Hey guys. I've never had a fuse blow on a tube amp before and I wanted to run it buy you guys before I turn it on again.

I was playing music (not loud) for maybe 1-2 minutes and my power conditioner cut the power on all the outlets and gave an "overload fault". First time that's happened so I did a quick inspection and nothing seemed out of the ordinary. I turned everything off and did a restart from source to amp. In the left channel amp, there was some slight static noise in the left speaker for a fraction of a second, I may have seen a tube flicker in the right front output tube but not really sure as it only lasted for a second and it was at the corner of my eye. It may have been the same tube that the original owner of the amp replaced. I immediately turned it off. I didn't try to turn it on again and immediately checked the fuse. It was blown. Right amp fuse is fine. I did a visual inspection of the tubes and I don't see any abnormalities.

This is my first tube amp so I don't want to do any damage. I have spare fuses. Should I just replace the fuse and see what happens? Not sure what else I could check before hand. Any input would be appreciated.

[AnotherJohnson]

Replace the fuse and watch the tubes on that side. One may look brighter on start up. Shut it down. Replace that tube.

Or, if you’ve got lots of fuses, replace the tubes one at a time until it doesn’t blow on start up.

I know there are folks who will disagree, but if it were me, I’d replace the lot of them. They’re probably all about the same age and hours. It will sound better with a full complement of new power tubes.

Be sure to replace fuses with the OEM rating.

[admin]

Thanks for the input. Thought about replacing all of them but eight kt120's are not that cheap.... and then it begs the question whether I should replace the right amp's as well to get them all the same age and matched... that would be 16! Yikes.

[roberto]

Admin,
First: don’t panic. You just replace the bad one. Remember to bring the bias adjustment screw totally counterclockwise. Always use the same rating Amp fuse. Turn the amp and of course you do know the rest.

AJ is all right. Great procedure and advice.
Happy listening

[roberto]

Admin,
The overload protection is a warnings of a big consumption. Yes, you have an intermittent tube failure.

The AJ advice is the right procedure.

Happy listening!

[SteveFord]

If you have a tube tester you can save a fuse, maybe.
If it won't bias, this bit from Manley might prove useful:
https://www.manley.com/tech-pages/cathode-resistor

[AnotherJohnson]

I keep 16+ KT120s on the shelf.

Yes, I would replace the lot of them. All 16.

Per hour, the cost of 16 tubes is typically less than $.50.

When one goes within a few hundred hours of being put into service, it’s an infant failure. In your case the failure is at a much later point. It is probably at the end of the constant hazard rate region. That means you are probably getting ready to go through this tube failure kabuki dance 15 more times in the next couple of hundred hours.

You can either pay now, or pay later after much aggravation.

If you don’t want to do this, I will happily buy your Arts for what you have in them. I’ll even pay the shipping.

[AnotherJohnson]

As you replace the tubes, console yourself with the fact that the tube R&R is a heck of a lot easier than sorting out a similar problem for solid state. Yes, transistors last longer as a rule … but when they fail, and they do fail, they create a lot more aggravation.

[SteveFord]

It may have been the same tube that the original owner of the amp replaced.

That's why I suggested look at the resistor, it sounds like this one socket may have a recurring issue.

[AnotherJohnson]

Or it could be the next one down as they go out following a Weibull distribution at the end of life.

I’d put money on the bet that there has been no resistor failure in these Arts, unless it was fused improperly and the failing tube was allowed to run away. And that’s not happened. The fuse blew as designed. The amp is safe. Count on it.

This is why we don’t buy aggravating stuff like AR or Manley.

[AnotherJohnson]

These are what you need.

https://upscaleaudio.com/collections/va ... -sol-kt120

Less than $900 for 16. Don’t bother with the cryo. Waste of money.

[AnotherJohnson]

If you’re feeling lucky, they are cheaper here.

https://vacuumtubevalues.com/product/tu ... r-burn-in/

If you buy from them, as Bobby has suggested, you can save about $250 on 16 of them. It wouldn’t be worth it to me … but it might be to you.

[admin]

Quick update. I didn't have a lot of time this morning but it was really bothering me so I replaced the fuse and powered up the unit very carefully. Saw the flash in the bad tube (which was not the same tube that the original owner replaced so hopefully just a regular tube failure and not some underlying issue). I looked in my box where I keep manuals and tubes, and what do you know, I had a spare tube. I had totally forgotten that the previous owner had included an extra tube. I put the tube in, changed the fuse (which had blown with me identifying the bad tube) and powered up the unit. Everything looked good. I let it warm up for a minute or two and did the biasing.

I didn't get a chance to listen to music or do the 30 minute in bias as I had to leave the house for some prior engagements. Tonight I am going to do some real music listening and bias the tubes (actually in both amps as it's been about 6 months since I did them last). I still have two fuses left and now zero replacement tubes.

I'm really considering just buying an entire set of new tubes for the heck of it plus some spare fuses. I'll have to look around and see my options. I'll update on my listening session tonight but with a little bit of luck we should be good (for at least a little while).

[AnotherJohnson]

Glad you had the spare. Now you’re a veteran.

There is no harm in replacing them one at a time. But I think you’ve entered the end of life regime. As long as you have fuses to spare, you might not mind the aggravation of one at a time replacement.

FWIW, the fuses aren’t free either. It takes about 32 to 48 fuses to sort out 16 one by one tube failures.

[roberto]

Tubes, when they start to fail, the silver and side colored, looks burnt. They should look bright when are good, not dark. This is just a guide. You can have a bad tube with just hours of use.
We all are tube users. We know that they are sometimes temperamental (lol). The good thing is: tubes are fantastic! Our ears had spoken.
All AJ comments are valid. The damage when a tube fails, usually the owner can replace and fix the problem. On SS, prepare your wallet.
Happy listening!

[SteveFord]

It's been a long time (knock on wood) that I had a tube actually fail. It lit up the room like a searchlight.
The culprit was the cheap trim pot that VTL was using back then.
I wound up having all of them replaced, I'm guessing c-j uses higher quality ones than those cheapies in the VTL.

[AnotherJohnson]

It's been a long time (knock on wood) that I had a tube actually fail. It lit up the room like a searchlight.
The culprit was the cheap trim pot that VTL was using back then.
I wound up having all of them replaced, I'm guessing c-j uses higher quality ones than those cheapies in the VTL.

CJ does pride themselves on using the best sounding, most reliable parts, especially in their upper level products.

When a tube lights up like a lightbulb, it often means that there is NO plate fuse, or the wrong rated plate fuse. The only time I’ve seen it was when I bought a used amp in which the previous owner had installed a fuse with 10 times the current carrying capability. I heard it first, saw it next, and dove through the air to the power outlet to unplug the amp.

Which tube was bad was obvious. I was surprised that the fuse hadn’t blown, so I removed the fuses and discovered the gross error. I called CJ and got several replacements, of which I ended up only needing one. Once I’d sorted that amp out, it went to another home.

[AnotherJohnson]

This is a decent thread about fuses in the audio path.

https://forum.audiogon.com/discussions/ ... protection

My ears tell me that CJ has figured out how to use fuses without compromising the sound.

[admin]

Lookin good guys. Got the new tube in there. Re-biased both amps. Did a 2 hour listening session and everything seems to be back to normal. (If you like the music of Hanz Zimmer, I would highly recommend this album: https://www.amazon.com/Worlds-Hans-Zimm ... 8&qid=&sr= All kinds of instruments and vocals to get a variety of sound.) After all of that it actually was pretty easy to identify the bad tube and take care of the problem. I certainly won't be this nervous the next time a tube fails.

I'm really divided on what to do about new tubes. If money was no object I would just get a full 16 new output tubes. But that's kind of a lot of money, even with the discounted tube store Roberto suggested (and AJ linked to above). And I would be replacing 16 currently functioning KT120 tubes. I'm currently saving my pennies in hopes of getting a used ET7 in the near future. I think that would be the next big step in taking the system to the next level. I've been checking every week for a unit to pop up at a reasonable price. It's nice to have these 1st world problems!

Anyways, thanks for everybody's input during this period of trying times!

[roberto]

admin,
Right now I am in Pagosa Springs Resort. It's cold here. We went to the thermal waters and the feeling for old bones is delicious.

Aj has good points regarding to buy the tubes from CJ or from his friend Kevin. All I can say is the burning procedure is the same everywhere. Then pairing them with the same gain, also is the same procedure. The brand of the KT-120s is Tung-Sol. Ask to Warren about his warranty. His price is very good, due that the price includes shipping and handling into the USA, I think they are very low price.

I had bought by now 12 KT-120s. And still no issues. Tubes are very uncertain. You don't know when they are going to fail.

Good to know that you were able to fix it!. As RJ says: enjoy those fine tunes!

Happy listening!