Audio Research VT100 Mk1, Mk3; VS115

Thanks for the link to the tutorial.   The ARC instructions for rebiasing the input tubes by themselves are useless. 

 I just replaced the 8 input tubes without rebiasing them.  I learned about the need to rebias them by accident,  it's not mentioned in the manual,  only on the ARC website.  The amp sounds fine the way it is.   If I get bored someday maybe I will set the bias correctly.   I did properly bias the output tubes, an almost trivial procedure compared with the input tubes. I hope I don't burn down my house because of a dangerous condition caused by improper biasing of my amplifier. 

I'm hoping to replace the amp before it needs new caps.  If I sell it I will definitely rebias everything. 

@richardp01

DO NOT USE THE AMP WITHOUT BIASING THE SIGNAL TUBES! Especially the driver tubes. Failure to bias the 6922 tubes will lead to damage of the amp. It may sound fine now but there is a good chance it is eating up the life of the new 6922 tubes. Also there is a good chance you are over driving a 6550 tube in each push pull circuit of a pair.

If you are lucky you will only blow a screen resistor/s. Of course because ARC installed the screen resistors against circuit traces there is the chance when the resistor/s blow the heat will damage the traces. At that point the amp is pretty much junk. You may also cause a driver tube/s to short which will cause it to take out a 6550 power tube/s.

Where did you buy the tubes? Each section of the 6922 tubes must be closely match. If Not you will spend hours moving the tubes around and may still never be able to bias the tubes to meet ARC design specs.


Best regards,
Jim.

Thanks Jim, 

You just ruined my evening.  The boxes the tubes came in had numbers for triodes1 and 2.  They were all marked either 80 and 85 or 85 and 80 for triodes 1 and 2.  I guess I have a plan for what to do tomorrow.

Rick

Rich, … I think Jim is giving you good advice.  I would like to reiterate what I posted.  Call ARC and talk to Evan.  Ask him what the best course of action is.  If Jim's assessment is correct, this is not a do-it-your-self'er.  

I can't make the economic call for you about whether you should movie up to the VS-115, but if your VT 100 MK I is long in the tooth and needs a retube (and possibly other work), I would call Evan and ask him if this is something you should attempt.  

If Evan tells you that retubing the VT 100 is like doing brain surgery on yourself, then an old Yoga Bera'ism comes to mind, "when you come to a fork in the road, take it."  Either send the VT 100 back to ARC (or an ARC authorized service station) or swap it for something else.

Been there and done it with many ARC products, including the VS 100, the VS-115, the Ref 150 SE and so forth.  ARC customer service is first rate.

BIF  

jea48

ARC installed the screen resistors against circuit traces there is the chance when the resistor/s blow the heat will damage the traces. At that point the amp is pretty much junk ...

That’s absurd. The amplifier will not be "pretty much junk" and can be readily repaired by a competent tech.