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Audio Research VS115 - click, snap -did it arc or not?

After many years of just enjoying reading all the knowledgeable posts here I now have a question on how to deal further with this amp. 
What happened? Set it up through the balanced inputs (removing the bridges) and connected Audiostatic ES300 speakers on the 4 ohm tap. Source is a dbx venu360 delivering everything above 100 Hz to the VS115, everything below to the subwoofer/amp. It plays nicely along until suddenly there is a pronounced click or snap, having read about resistors being taken out when tubes go bad on ARC equipment I immediately darted off and yanked the power cord from the outlet. There was no smoke or bad smell, but I let it sit for a couple hours and then proceeded to take of the plate and found nothing burnt on a visual inspect. Next was a simple check of each tube for filament and shorts (checking each possible connection with a mulitmeter it should only return low resistance for 2 and 7 for the KT120 and 4 and 5 for the 6H30). All turned out fine. So now I am wondering what really happened and how to proceed, out of my location sending it to the manufacturer or finding a technician is not my first choice.
Assumption A is that all I heard was the relay (which comes on 5 secs after power on, I couldn't find a reference to it in the manual but would assume it is a plop protection for the speakers) and have to wonder under what conditions it would come off (undervoltage or exceeding current to the speakers)?
Assumption B is that something "went" and needs to be found out. Would you take out the tubes and go part by part and compare value vs. measurement on resistors, caps etc. I do know that in a network values will interact, but a failed component may come up, drawback is the amount of time involved. Alternatively power it up connected but with no signal and measure each bias output (on the back)...all the while ready to yank the power cord immediately.

Cheers
Brxl 
brxl
brxl OP
21 posts
 
Thanks BIF for reminding me. I will wait for ARC's email response. Good questions...I had checked and set the bias a couple days before and listened on the 8ohm taps to some ESL-63s with no occurences.
To narrow it down...the Audiostatic draws quite some current (it is very much a capacitor) and I also had it on the 4 ohm tap, where I think it should be (3.7 min imp. at around 11kHz).
On the VS115 there is one pot per tube pair, measurement on one then the other, made sure neither was above 63mV, so I believe that to be good.
Again, no burns on any part, no smell. I do not know if it works, I just darted and yanked the power supply. I did not turn it on (and in case the relay came off because of undervoltage am looking at a functioning amp while being scared to turn it on ;-)
I am contemplating turning it on with everything connected, no signal, I probably even find 4-6 multimeters (not 8 though) and just watch... always ready to yank the power cord again :-)
But let's wait until tomorrow and give them a chance to reply after I started the email process,
cheers
brxl
brxl OP
21 posts
 
Greg has been very helpful. Turns out the resistors that go "puff" are on the underside, et voila one is burnt.
I may solder in a new one and carefully check how crazy the readings for V1 and V3 (V3's resistor went) turn out.

The current sets are KT120s from tubestore. I don't know how old.

As a next item a new matched pair V1/V3 may be the minimal step. Tempted to try getting a matched quad of 6550s and pair it with the existing quad of Shuguang 6550 As, although they have not received much applause in my other thread. 
bifwynne
2,206 posts
 
brxl, ... looks like you sourced the problem.  I suggest that you buy a pair of ARC KT-120s to replace the affect pair, .... after you replace the blown resister(s). 

ARC matched tubes are as good as it gets.  If too expensive, pick up a quad from Upscale Audio and buy the ARC select grade.  Forget the cryo treatment.

Please advise on how you make out.   
brxl OP
21 posts
 
I replaced the resistor and carefully watched the bias, nothing noteworthy so far and it is back playing.
The tubes should have 400 hours on them. I will get a matched pair from tubestore (as that is the source for the other 6 tubes that had no quirks) ...just in case. Also on order 2 matched pairs of Shuguang 6550As to be tried out with the 20 year old ones I already have. 
atmasphere's avatar
atmasphere
11,783 posts
 
Sounds like a tube arced (if you will pardon the expression) and took out the resistor. After some handling of the tubes, the arc is probably temporarily cleared, but I would not be surprised to hear that if the tube were placed back in service that this happened again.


The time on the tube is irrelevant- get it replaced. For best results get a matched pair. ARC does pretty stringent testing so expect to pay a bit more for their tubes, but I would also expect them to hold up better.
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