DOA tube from Audio Research


I just opened a matched quad set of 6550 tubes I bought last year from ARC and one of them is DOA. How can this have happened? I thought they were the most highly screened and tested tubes available. Has anyone else ever had this happen? I immediately called their support line and got the support guys voice mail saying he is on vacation. This is really frustrating. I've been waiting until I had some spare time to listen at length to the KT88s I put in last year before I switched over to the new 6550s. DAMN IT!!!

VPI Classic, Rotel DAC, ARC SP17, ARC VS60, Golden Ear Triton 2s, Nordost and Shunyata. A reasonably decent system that I rarely have time to listen to.
dfwlistener
ARC VS60

DOA?
The filament is open?
The tube arced and shorted out? If so did you back off the tube bias adjustments before installing the new power tubes?

ARC VS60 manual
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Try a different tube in the same socket just to make sure nothing was damaged when you installed the new ones.
Good points Jea48. Also did the OP switch the tubes around to make sure that the problem is the tube and not a burned resister.

Btw, there may be an opportunity here. I just checked the ARCDB web site -- News Tab. If you scroll down far enough, the site reports that when ARC cleared KT-120 tubes for use in some of its older 6550 tube amps, the VSI60 was listed. The VS60 was not specifically mentioned. That said, if the innards of the VS60 are the same as the amp part of the innards of the VSI60, going from the 6550 to the KT-120 in the VS60 could make a big improvement.

As an aside, a number of 3rd party tube vendors sell the KT-120 for about $50 a pop. The 6550s might be more expensive depending on the brand. Be careful with so called "original" SED Winged Cs. Many of these SED Winged Cs on the market today are sub par grade. Check out the Upscale Audio web site for the full story.

Dfwlistener ... I sent Kal a message over the weekend about a tube inquiry. Kal's Outlook mailbox sent me an auto response saying that he is on vacation until Wednesday, the 22nd. Try back then.

But please keep in mind my suggestion about switching tubes around to confirm that the problem is the tube and not a burned resister. Also, when you hook up with Kal, ask him if the KT-120 is cleared for the VS60. I do not think you will be disappointed.

FWIW, I used to own the VS-115 which came stock with 6550s. ARC cleared the VS-115 for KT-120s. IMO, it made a dramatic difference for the better.

Cheers,

BIF
Thats why i use a solid state amp and tube preamp.
Ebm,
As Ronald Reagan used to say, "There you go again."
I received a DOA 6h30 from them last year. They replaced it for me.
Ronald Reagan was a big jerk DUDE!!!!
Who's Ronald Reagan? Was he an audiophile?
You should always try out tubes when you get them. Audio Research might just tell you that they are a year old. How would you prove to them that they were never used?
Thanks for the responses guys. I have a compu-bias meter. I didn't change the bias at all from where it was which by the way was on the low side of what the manual recommends. There is no recommendation to reduce bias before tube installation anywhere in the manual. The amp comes from the factory already biased. And yes I did swap sockets and confirm that it was the tube and not a blown resistor. I got a call back yesterday from one of the other ARC guys and he had me send an email to their service department. Th tube was definitely DOA as you can easily see the slow turn on and ramp of the bias current and output power with the comps-bias meter. It didn't arc, pop or any other telltale of failing on installation.

I've been wondering about the use of the KT120s. Thanks for the info BIF. I will definitely inquire with the service guy when we communicate. My local ARC dealer actually suggested the same thing last year. What kind of difference did you hear?
I do agree with Yogiboy. even if you have no intention of using the new tubes anytime soon, you should test them in circuit and see if they work. That way, the company you purchased them from will honor whatever warranty that comes with the tubes. No way can the company tell six months later that you didn't use or abuse the tubes.

In any case, tubes blow. bumping them, dropping them, shipping them, etc. may cause problems. I'm sure AR did as they always do, they tested and matched the tubes before shipping. But @@$$% happens. I'm curious as to why you posted this complaint? Are you upset with the tube? letting it sit for six months before testing it and losing the warranty? upset with AR?

I understand frustration over things breaking, but that is the nature of the beast. Car parts will break. I don't care if it is a Toyota, Nissan, Porsche, etc. Watches break, audio components break. I know people that never maintain their cars, yet complain when they break. They had ample warning to do something, but they are sooo mad when it breaks. As if they were designed to last forever.

Tubes are especially fragile. One of the major reasons why many people want solid state. But oh, with the right tube gear... the sound is wonderful.

I just purchased a pair of AR REF250 amps from my favorite dealer. I've been listening to these amps for two years at my dealer saying that if I ever could really afford them, I would get them.

Well, I did. Took them home, connected them and found one V1 tube blown. What the $$**? Two years of perfect listening at the store on the same amps and take them home and blown tube. Demonstration units. Covered by warranty. Get new tube under warranty and move on.

Best amps I have ever heard.

Had tube amps before. ##$$$ happens.

Sorry for the tube issue you experienced. Not an AR issue. get a new tube, plug it in. Bias it. Listen to great music and move on.

enjoy

I have a compu-bias meter. I didn't change the bias at all from where it was which by the way was on the low side of what the manual recommends.
07-22-15: Dfwlistener

compu-bias meter

Dfwlistener,

Would you please post back what ARC's service department response to the use of compu-bias meter is.

There is no recommendation to reduce bias before tube installation anywhere in the manual. The amp comes from the factory already biased.

No there is not. But normally as the power tubes age they need to be re-biased as they age and get near their end of life. You never re-biased the 6550 tubes that came with the amp since it was new?

IF you had re-biased the 6550 tubes you would have increased the settings of the bias pots. And that is why you reduce the setting of the bias pots before installing new power tubes. If not you could damage the new tubes.

Just curious after using the compu-bias meter did you ever check the bias setting with a 3 1/2 digit meter to see if the bias was set at 60mVDC, (.060 Volt DC), as per ARC specs?

As for running the bias below the recommended 60mVDC I can't speak for the VS60, but I can for the ARC VT50 amp using 6550 power tubes. ARC specs 65mVDC. If the bias is set at ,say 60mVDC the SQ loses upper end detail and the bass is not as tight. Midrange is softer. The Amp sounds best when the bias for each channel is set at 65mVDC.

As for the ARC manual,.... ARC leaves a lot to the imagination, imo. I think ARC figures if you are buying one of their amps, that is not an auto bias amp, the user must therefore know how to bias the amp.

I bought my ARC VT50 new in 1997. No where in the manual does it say anything about biasing the 4) 6922 tubes in the amp when re-tubing the 6922 tubes. But they do have to be....

Hard to believe you never checked/reset the bias on the 6550 tubes that came with the amp.
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ARC service (Kal) says "no problem" using the computer-bias. It measures plate V, cathode I and dissipation power on a pair of tubes simultaneously. Per my original post, I had replaced the original tubes last year with KT 88s and set the bias at 60 mv / 60 ma. I ordered the new set of ARC 6550s in December because I thought the KT88s were a little too warm sounding. I haven't had the time until last week to sit down at length and listen to the 88s and then do the switch while trying to maintain some aural memory. Some one suggested I should have turned the bias down prior to installation and copied the ARC manual in the post. The implication being that I had somehow made a known mistake in installation and that may have caused the tube to blow. There's no reference in the manual to doing such a thing. In contrast, the amp ships with the tubes in a separate box and requires the owner to install them in a factory biased amp. The turn on circuit has some amount of current ramp up delay in it which can be easily observed using the compu-bias. I had not re biased the 88s since installation but when I initially installed the new 6550s, I noticed the bias was on the low side (for the ones that worked). When I reinstalled the 88s I realized that they in fact we're running quite low (only 17 watts). So I re biased them to (25 watts) and proceeded to listen. WOW. You are right. The difference was dramatic. Everything sounded better. So in the meantime, ARC is sending me a replacement tube at a discount. Bad on me for not noticing the warranty. I realize tubes are somewhat fragile but I seriously doubt that the overall failure rate of all tubed products is 25% due to shipping damage. Therefore my conclusion that this tube somehow escaped the factory in a faulty condition and my ensuing frustration. But as you said, $..t happens.

As for using KT120s in this amp, Kal says it will work but the power supply transformer will be substantially over worked and will likely fail early due to significant overheating.

Thanks for all the responses. This is my first tubed amp and I'm getting initiated to all the issues involved. That said, I still think tubed power is far preferable to the alternative when it comes to music.

Some one suggested I should have turned the bias down prior to installation and copied the ARC manual in the post. The implication being that I had somehow made a known mistake in installation and that may have caused the tube to blow. There's no reference in the manual to doing such a thing. In contrast, the amp ships with the tubes in a separate box and requires the owner to install them in a factory biased amp.
07-24-15: Dfwlistener
Dfwlistener,

The power tubes that were shipped with the amp are the tubes that were used to bias the amp.

By chance did you ask Kal, of ARC, after the new 6550 tubes were biased for the amp does the bias ever need to be checked or readjusted? Do the power tubes need to be checked for proper bias after say, 50 hours of use, or 100 hours of use, or maybe 500 hours of use? Or even 1000 hours of use?
I suggest you call or email Kal and ask him about checking and readjusting the bias of the power tubes as they age from hours of use. Like I said in an earlier post the user ARC manual leaves a lot to the imagination.

As for your original post I assumed you were replacing the power tubes because the old tubes were near their end of life. (Approximately 2000 hours of use). If that was the case and normally the user of the amp would have reset the bias of the power tubes as they reached their end of life, before installing new fresh power tubes the bias pots should be turned, adjusted back, before installing the new tubes.
Ask Kal if you contact him again.

Some reading material for you.

What is the Bias Point?

>>>>>>>>>>

Quote from Link below.
When installing fresh power tubes, you have to remember that your old tubes likely required less negative bias to maintain the same idle current as they aged. Before plugging in your fresh set of power tubes, you may want to adjust the bias so the reading on your meter is lower before plugging in the new tubes!

This is a very important step. If you have the bias setting turned up too high (technically the negative bias is too low, causing your meter to read a higher number), it may let the tubes get away from you once the amp is on. In some amps, this can result in a burnt fuse. or worse yet, a burnt resistor. If your amp uses a cathode or auto-biasing circuit, then you don't have to sweat this step, but if you adjust bias manually it is very important.
Upscale Audio FAQ
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I have owned ARC tube amps for almost 30 years. ARC manuals are really not all that helpful. You just have to learn from experience as you go. Here are some Basic rules that I go by.

Turn the bias way down when installing new tubes. You don't want a tube running with a high bias while the amp arms up.

The amp needs to warm up before checking the bias. I usually let mine warm up for about 30 minutes. Or check after a listening session.

When checking the bias the amp should be idle with no music playing. Let it settle for a few minutes if you were playing music.

Tube can drift quite a lot, especially when the tubes are new. You need to check the bias often when tubes are new.

After the tube have settled in I still check my bias once a month or so.

If tubes run hot they will not last as long. Also they have a greater chance of arcing. Checking the bias is cheap insurance. I am not familiar with the compu-bias meter, I have always used a multi meter. It might not be a bad idea to double check the bias with a multi meter. Just to see how accurate the compu-bias meter readings are. Tube amps are far more work than solid-state but I think they are well worth the trouble.