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ARC VT-50 Damage/Repair Advice

Forgive me in advance, for the very long post. But I am simply copying and pasting, what I posted at another forum...and they suggested I might get some good advice/feedback here.

Here goes:

I need some advice. There's no right or wrong answer; just opinions...though you do have to put yourself in my shoes a bit.

I purchased this used ARC VT-50 tube power-amp; as I am wont to do. You know how I roll: something catches my eye, or I have a need; I buy, I try...and some stuff sticks, and some stuff flips...lol.

Now...this is an "older" unit; point being, it has "manual" biasing. I'm not the world's foremost expert on tube biasing; so before I even unpacked it, or fired it up...I brought the amp into my office...and had some of the "techs" help me with it. We turned it on, waited 15 minutes...and tested the voltage. Left side was stable and spot-on; right side was a little wobbly. So we waited another 45 minutes or so (per manual...you should measure at 15 minutes and 1 hour).

At the 15 minute mark, I had the "tech" do it...so I could watch, and make sure there wasn't much to it. You just take your voltmeter leads, and touch them to each side of a test resistor. But at the 1 hour mark...I decided to give it a try. I swear...it seems all I did, was touch the 2 voltmeter leads to the test points; just as I had seen the other guy do it. But I must have shaky hands or something...because I got a pop that nearly made me sh*te me pants!

So I shut it down right away, and packed it right back up to be repaired at ARC. It looked to me...the untrained eye...that the damage was minimal; some noticeable burn, down on the tracer circuit...where things arced from the test point. And I talked to the previous owner, and he said he's arc'ed a tracer board before (not necessarily on the same unit); so I didn't feel like a total idiot.

Of course, I was hopeful and optimistic...that the repair, and therefore cost, would be minimal. After all: I had just bought this piece used, to "try out"; and now was having to shell-out for a repair bill...before I even had a chance to hear it, and/or flip it.

I didn't hear from ARC for a spell; so I just dropped them a polite line, to see if they had an update for me. Word came back "technician says unit has extensive PC board damage and will need a tube set. [tech name] is in the process of working up an estimate. Should have more info later in the week”.

Yikes; not, at all, wanted I wanted to hear. I'm especially surprised...by the need for a new tube set? Describing the incident that occurred; it didn't seem possible I could have blown all 8 tubes!!?? I asked the ARC forum, from another board...if ARC is pretty reputable, for giving it to you straight? Not that I had any doubts. I mean...ARC has been around forever, and I happen to love their kit.

One guy in particular said "they ain't cheap; but...", and I'll paraphrase here...they're not going to rip you off, by padding the bill or claiming unnecessary repairs.

OK, well; with a statement like that...maybe I shouldn't have been surprised. I mean...I was prepared for the "worst", but hopeful for the best. Well...you think I'm making this post, if the news turned out to be the latter?

I don't usually get into numbers...but for this discussion; the numbers are important. $1100 is what I was quoted for the repair...AND new set of tubes. Now I get it; a technician at a "reputable" house, like ARC...doesn't want to leave anything to chance. They want to replace ALL damaged parts...go ahead and put in a set of tubes, they KNOW they can trust (even though this incident occurred, when I was biasing the right channel. So even if I blew EVERYTHING on that side...which I wouldn't even bet on; I would be very surprised, if the 2 input tubes and 2 output tubes on the left side, were also "blown"); bias, tune...and send it back to you, knowing it's in tip-top shape.

Out of curiously, I asked the gal who is the admin for the Support department; if she could give me a "line-item" cost, on the tube set. Now again...let me reiterate: ARC...fine, fine company; and their policy and cost, is their policy and cost. I do not post this here to denigrate them; in fact...I usually keep my "dealings" pretty private. But they want $560 for the tubes!

Now...when this amp was on its way; I was already thinking about rolling something into the 6550 slots. Of course, the "best" 6550 known to be going right now...is the Svetlana "Winged" 6550C. But I already had a problem with them of late...and even the guy from Upscale said "smart to stay away"; because evidently, as they were stopping production, they really cut corners on QA at the end...so it's a dice-roll. He recommended Sovtek 6550WE, and even said "that's what ARC is using...now that the Svetlana Cs are out of production". Cost? $32/per; and that's retail, from Upscale! Let me do the math for ya; that's $128, for the Quad...American!!

Now...I don't know what ARC is using in the input slots (4 x 6922s); but I doubt it's anything "exotic". A) "stock" tubes usually aren't, and B) those "tech/engineer" types; they usually don't even think it makes any difference, lol. They often choose, based on reliability; not any audiophile mumbo-jumbo about NOS glass magic, lol. So let's say...they were going to go with something, like the EH Gold Pin? Cost? $25/per; and again...that's retail, and that's at Upscale, etc., etc.

So how can ARC justify charging me, $560; for $228 "worth" of tubes...retail? Well, like I said; they do what they do...and if you want to play the game, which is have them stand 1000% behind the work. You have to pay the price of admission.

So I asked them...is there any way, for them to repair this thing...without the fresh set of tubes? I mean...I understand they need tubes to test it, after repair; but couldn't they use some kind of house "testers", and then send it back tube-less? I mean...this MIGHT end up staying (I actually bought it, because I have a Wyred STP-SE pre-amp...that I think has potential; but needed some warmth, in the way of a tube amp). OTOH...I might just want to sell this thing (as I am again, wont to do).

On top of everything else; I actually already have...(4) 6922s I could use. So I'd cut my repair bill in HALF, and at worst...I'd be looking at ~$130 for a new quad of 6550s. Or...I might just cut bait, sell it advertised as "repaired by ARC; sans tubes...new owner, roll your own".

Sure...if I bought this new, treasured this amp, and were going to leave it to my kids; I'd let ARC do their thing, and know I had a finely-tuned machine...that I wasn't going to have to turn around and bias again (at least not right away). But this ain't that.

I wasn't even sure ARC would consider it; but I got word today..."Per our technician, you will receive NO SERVICE WARRANTY WHATSOEVER, if you choose this course of action. If the unit is damaged as a result of your tubes, you will be fully responsible for another repair and shipping both ways.” CYA and fear of god accomplished, lol.

I don't know; it's sure attractive...to cut that repair cost in half (for the record...the full cost of the repair, is damn near what I paid for the amp to begin with!)...get some tubes, AND some HELP! And just very carefully, try to get this thing back in good working order; without losing my shirt.

Now...another suggestion I've been given, is asking ARC if they will repair, and bias; with MY tubes. The 4 existing 6922s I have...and a new Quad of (reputable) 6550s, I would purchase. I think that's an excellent compromise; but IDK. Is that a little like bringing your own steak to a restaurant...and asking them to cook it for you? You know...because their mark-up is too high, lol.

It has also been suggested to me...that it is a SURPRISING amount of damage; to have "slipped" (if that's even what I did)...off the test resistor.

Trying to make a decision, one way or another, quickly; just feel confused and conflicted about my best course of action. Thanks for any feedback or advice!

CD
128x128hiendpawn
jea48
4,424 posts
 
At the 15 minute mark, I had the "tech" do it...so I could watch, and make sure there wasn't much to it. You just take your voltmeter leads, and touch them to each side of a test resistor. But at the 1 hour mark...I decided to give it a try. I swear...it seems all I did, was touch the 2 voltmeter leads to the test points; just as I had seen the other guy do it. But I must have shaky hands or something...because I got a pop that nearly made me sh*te me pants!

Hiendpawn,

Just guessing you shorted the B+ 420Vdc to the silver color Phillips head circuit board mounting screw just above the right hand side of the bias resistor.

When you get the amp back from ARC I suggest you buy a pair of hook on clips for your multimeter.
Examples of.

As for the tubes it sounds like the 6550 tubes were near their end of life. Good chance so were the 6922 tubes.

You can't just drop in new 6922 tubes in the VT50 amp. The new 6922 tubes need to be biased.

And you MUST have closely matched 6922 tubes. Especially the driver tubes. Not only matched pairs for each channel but each section of the dual triode tube must be closely matched. If each section of the tube is not closely matched you will never be able to bias the input and driver tube for each channel. (Behind each channel side panel there are 3 bias trim pots.)

The VT50 is no where near as hard to bias as VT100 MK 1 and Mk 2 but it still can be a pain if you do not start out with closely matched 6922 tubes.

You may complain about ARC tube pricing but you would probably be surprised how many 6922 tubes they go through to get closely matched triode sections let alone matched pairs.
VT50 setup instructions with complete retube.
.
czarivey
5,946 posts
 
One day I brought my Volvo to techie to as how mow will
be to fix my AC. They took a look and told $850 coz I
needed to replace whole compressor and lines as well.
Instead I repaired compressor myself for $15 and saved
$835.

Another day I had dropped spinning grinder onto my big
toe and cut it all the way down to the bone. After the
doctor checked he decided to remove the toe. Instead of
going under the blade or saw, I started applying
bacterial ointment that 'eats out' infection and got
myself healed instead of cut.

Each statement can be tested for truth.
lostbears's avatar
lostbears
538 posts
 

Bifwynne, Both of those are very nice amps. The Ref 110 is getting to be a real bargain at a little over $4000. Put KT120 tubes in it and you have a seriously great sounding amp for a really nice price. I know, I own one.

The VS 115 is also a nice amp and better sounding than the earlier 110. I like the look of the "flat tops" with the tubes out in front. Not as easy to find as the Ref 110 though. Both are really easy to bias with bias ports.

One of the things with the VT50 is that it is just not that powerful. Even for a 50 watt tube amp. You need efficient speaker to get the best sound. I prefer a bit more power even with fairly efficient speakers. My speakers are around 93db and I use a ref 110 to drive them.
hiendpawn's avatar
hiendpawn OP
7 posts
 
Jea48


When you get the amp back from ARC I suggest you buy a pair of hook on clips for your multimeter.>

I think you're exactly right, about hitting that screw. I have a picture of the resistor and damage, from right after; and that's the only thing I could think of as well.

As for the "alligator clips"; there is NO question...lol.



In hindsight, I'm not really complaining as much; and I was never "accusing". Let's be honest: most guys, who can afford kit like ARC...could give a sh*t, about a few hundred bucks. And as I've said...if this was an amp, I was SURE was staying; I probably would bite the bullet, and let ARC do their thing (because I now understand, at least a bit better...why they charge much more than a tube dealer).

But I've been clear about why that's not the case here.

For the record...they have agreed, to let me send them new tubes; and repair and "try" to bias from them. I say "try", because they have warned me...they will be testing the tubes, and reserve the right to reject anything they don't feel is up to snuff.

I'm down with that; I mean...I don't want "junk" in the amp either, keeper or not. I just hope they don't go CRAZY stringent in this case. I'm getting 4 Sovteks and 4 EH Golds, and having them sent right to ARC.

As for the many suggestions...I could do "better", than the VT-50. First of all...duh, lol. I'm a guy, who's been an avid box-swapper; and I'm trying to hone in on something to just "be happy" with.

Like right now...after many, many other boxes, have passed through the rack; I have a Luxman L-550AX, Ayre AX-7e...and I have a Wyred STP-SE, that I think might have potential.

I usually go the other way around; tube pre into SS muscle. But for the exceptionally clean STP...I decided to try tube power. So I wasn't going to break the bank to "experiment"...and, I've heard the VT-50 is a sweet, little guy :)

But trust me...if this combo worked out, and I was going to move up the ARC ladder; I'd buy a Ref 75 in a second!

CD
jea48
4,424 posts
 
Hiendpawn,

I bought my VT50 amp new in 1997.

Unless you listen to music really loud 45 watts per channel should be fine. At present I am running EH 6922 tubes and a quad of SED Winged C 6550C tubes I bought from Upscale Audio back in 2007 I had stashed away until about a year ago when I then installed them in the amp.

Before the SED 6550 tubes I ran all EH tubes.

If you are buying the new 6922 tubes from Upscale Audio tell them you need the two pairs closely matched and the two sections of the 6922 MUST BE closely matched. If the 2 sections of each tube are not closely match ARC will not be able to bias the tubes within the circuit design specs of the amp and will reject the tubes.

Closely matched pairs or a quad of the 6550 tubes is the easy part.

Also worth mentioning I doubt ARC will be installing a new right channel circuit board. Even if they still had one in stock I would be willing to bet they would want at least $1500 for it plus installation. They will repair the damaged caused by shorting the B+ 420 Vdc to the B- chassis connected power supply rail. The B- is connected to the chassis through a 10 ohm resistor that was more than likely also taken out by the short.

SoundStage review.

The basic circuit of the VT50 is the long-lived ARC ultralinear, partial-cathode-coupled design. TheVT50/100/200 series, which debuted about four years or so ago, saw the addition of FETs to the traditional circuit, employed as a constant current source. According to ARC, this allows for greater linearity, most especially when using the single-ended inputs (the design is both balanced and dual mono from the power supply forward). Other changes in layout and design allowed for better heat dissipation, with a payoff in greater reliability and longer life. Energy storage was also increased, with the VT50 boasting 354 joules worth.

The VT50 does have a hefty power transformer and DC power supplies. When turning the amp on or off don't dally around when flipping the rocker switch on or off. Flip it in a quick fast motion.
Jim
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