DOA tube from Audio Research

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.
.

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.