|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
104.231.213.75
I have an Audio Research VT 60 that's been sitting in a closet for 5+ years that I wanted to start listening to again as I'm making some system changes. When I turn it on, the green power light comes on for a split second then goes off. The four 6550 tubes continue to light up, along with the left and right 6922 tubes, but the center 6922 stays off. No sound. Is this tube likely the problem? Or worse could it be the amp that's messed up. I know close to nothing about tubes beyond they light up, get hot, and sound good when they work. What is the function of the three smaller tubes on a power amp? I guess I can start by replacing that one tube and see what happens. Could there be another issue when an amp sits for a while? Or is it an age issue with tubes and maybe they all might need to be replaced. I think the tubes were replaced before I purchased the amp and I put very few hours on it before I switched to a solid state Meridian.
Edits: 01/15/15 01/15/15Follow Ups:
Here is a link to the schematic from ARC's web site. ARC now has all their legacy product schematics and manuals on their web site.
It sounds like regulator U2 has failed. This would explain why the power indicator lamp does not light and the heater does not light on the input tube.
http://www.audioresearch.com/ContentsFiles/VT60%20SchPL.pdf
I found a website and also watched a youtube video to learn how to check a regulator(I had no clue). I turned the amp on, set my multimeter and from input to ground I got about 12v, and from ground to output I got ZERO !!!! I might try to change this myself. Do I need a special brand or can I just use any regulator with the correct # (MC7808)? Hopefully there isn't something else going on up or downstream that will take out the new regulator once it's in. Thanks so much!
I would purchase the regulator from ARC. It won't be that much money and you will know you have the right device.
There is not that much going on with the circuit and likely nothing else has failed. Good input voltage suggests everything is working properly before the regulator.
A tube arc could damage the regulator. You might go ahead and replace the V1 tube just to be safe.
Good news is it's not the tubes. The bad news is IT'S NOT THE TUBES! Swapped 'em around and any tube in the center socket doesn't light up. Is the socket my next target? I have good soldering abilities but do I want to tackle that myself? After I turned the amp off, I put my pinky in there when the tube was out and touched the circuit board just behind the socket to check the amount of dust....DON'T DO THAT!!!!! OUCH :-(
The only thing it can be is a tube socket or maybe you need to tighten the pins at number 4 and 5 and you can do that with a tiny jeweler's screwdriver but bending them in a bit..There is a youtube video that shows you how to do this..Some of the Russian 6922s have smaller diameter pins and when the pins get stretched out a bit they won't make contact..Putting in a different 6922 in that position with larger pins like a JJ can also solve your problem.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Tightened up all the pins with my soldering poker tool and got it pretty darn snug, but still not working. I tested the connections between the pin and the nearest solder below the socket and the all were ok. I then put the tube in part way and tested from the top of the pin just below the glass thru to the solder and nearest resistor and that was also ok. I tested every resistor and connection associated with that center tube socket and all checked out. I also did a visual inspection of the top and bottom of the circuit board to look for dirt or hair anything crossing paths for a short circuit and found nothing. Don't know what else to try.
I'm no technician, but your input tube (the one in the middle) is essentially tied in with everything else. So a problem anywhere else may be causing the protection circuit to kick in to prevent the input section to fire up and cause damage.
Just a theory.
Bottom line is you may have to check everything.
Cleaning all the sockets and pins may be necessary.
It won't hurt.
Also, I myself am not good at reading schematics, but I'm giving you a link you may already have. It has some info on your amp.
Good luck and keep us posted.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Put a black sharpie dot on the potentially problematic 6922. Swap it and another one of the 6922's. If the tube with the dot continues to stay dark, but another 6922. If the center to ensure stays dim, you'll want to get the socket repaired.
By the way, if the silver part of the 6922 has turned white, be sure to toss it.
Tightened up the pin openings with my soldering poker tool until it was more snug, but still not working. I tested the connections between the pin and the solder locations below the socket and they were ok. I put the tube in part way and tested from the top of the exposed pin just below the glass thru to the solder and then to the nearest resistor and that was also ok. I tested each visible resistor and contact that connects to that center socket and all checked out. I also did a visual inspection of the top and bottom of the circuit board to look for dirt or hair anything crossing paths for a short circuit and found nothing. Don't know what else to try. I tried to drop an email to service at ARC
but it's not working on their site, so I sent it to their general email and asked them to forward it, haven't heard back yet.
Oxidation develops on the contacts when they sit. Wiggle it in the socket, or remove it and plug it back in to see if that changes anything.
He ought to just reverse it with one of the other 6922s to see if it lights up in that socket.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
I was afraid to swap a good tube into a potentially bad socket and trash that one too. An employee at the dealer where i got the ARC said he'd be interested in possibly purchasing my VT60 for $400 or so for himself (GIMME A %$&! BREAK) and said it would need new tubes from sitting so long. I also read on the asylum that tubes can sit for decades and still be good. Don't really want to swap out every tube unless i really have to. $400, really? There was one sitting a few feet away from me on a rack at their store they just sold for $995. Not to mention I made mine a smokin' cool cover(that cage had to go)
Even if there is something wrong inside the amp causing it to eat the tube, it's doubtful that it would burn out the heater.
Exactly.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
You should email Arc about that dealer. That would've been a giant disservice to you.
I think this particular guy does repairs for the dealer, he was there when i was looking at headphones. He wanted to buy it for personal use I think. I know they need to make money on trade-ins but yeesh, that makes it no more valuable than the tubes that are in it. From what i gathered thru observation, it seems like dealers(or at least this one) gives about 25-30% on a trade in for older stuff and then sells it for 1/2 retail.
Edits: 01/16/15
Yes
The 6922 could very well be the problem.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
OP: Order a whole new set of small signal tubes from Jim McShane. Pull the old ones out (gently by the bases), put the new ones in. At least get a pair of relatively well-matched 6922s, but it might be best just to replace all the small signal tubes (the 3 in front).
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Shouldn't the power light still stay on, even with a bad tube?
I thought you might be talking about filaments, since you said you knew nothing about tubes. I don't have any power lights and so i didn't think about actual power lights.
Cleaning the sockets and pins on the tubes may help.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
The ARC products use sensing circuits to make sure everything is right before it turns the unit on.It is in shut down because its sensing a problem with that tube most likely.Try pulling that tube out and reinserting it or clean the socket with a little dexoit from Radio Shack.It may have a little oxidation from sitting but if not,the tube is bad..I wouldn't suspect a bad solder connection as ARC doesn't typically have those but it is most likely in that tube..You could also take one of the other 6922s out and reverse it with that one to see if it lights up.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Edits: 01/16/15
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: