What led me to think of the possibility that speakers might not have been connected was the statement in the original post that "I brought the amp into my office...and had some of the 'techs' help me with it...."Good Job Al!
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
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
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- 36 posts total
Thanks, Kng. And thanks Jim for providing the info. I suppose it's possible that the physical placement of the rectifier circuit and the filter capacitors could have provided some reduction in the likelihood that a short to that screw would have affected the other channel, due to the small amount of resistance and inductance in the interconnections within the amp. But given that all of those things are electrically connected together for both channels, my point is simply that it is not implausible that the momentary short could have affected the output tubes of both channels. Hiendpawn, not having the speakers or an equivalent load connected would not affect the bias adjustments. It would also not result in a risk of damage, UNLESS a "signal" or some kind of equivalent is put through the output stage of the amp. In this case the momentary short that apparently occurred might have constituted such a "signal." Also, a significant turn-on or turn-off transient that might be generated by some amps, either as a result of its design or as a result of some issue relating to its condition, might constitute such a "signal." For example, I once had a high powered solid state amp that produced a wicked thump in the speakers about 40 seconds after it was turned off, although of course in the case of that solid state amp inductive kickback would not have been an issue since there was no output transformer. Best regards, -- Al |
Wow Jim. Just looked at the close up pic showing the Phillips screw and the bias resister contacts. Small wonder the OP shorted his amp. You need 4 hands to bias that old clunker. My ARC amp has multi-meter probe sockets. Avoids (or at least mitigates) the chances for a short. So far, never had a problem. Tell ya one thing about the Ref 150's 1040 joule power supply. A couple of months ago, I accidentally got shocked while putting the top back on my amp. Hit a power supply cap with my finger. My hair curled and I am lucky that that's all that happened. |
Bifwynne, Yes, that is why a pair of hook on probes should be used when biasing the amp. Sometimes I think the guy that designed the layout of the amp had a sick sense of humor. Also as I stated in an earlier post the bias adjust pots are really touchy. The slightest movement can really swing the bias voltage one way or the other. Both hands are needed to adjust the pots. LOL, Heaven help the guy that has the shakes. And when biasing the 6922 input and driver tubes the hook on probes are a must. (Though those pots are not touchy.) As for the amp being an old clunker, LOL, even though it is 18 years old it has served this old clunker well, lol. I would still put it up against some of the new stuff on the market today. . Jim |
Hi Al,
Al, That was not a thought in my mind when supplying you the pictures. I take you at your word that the OP could have caused damage to the power tubes. I just thought you might want to see what was under the hood of the VT50. The amp is built like a tank, but with that said, jmho, it is not layman maintenance service friendly. . Jim |
- 36 posts total