Audio Research VT100 Mk1, Mk3; VS115

@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.

Richard, in your original post, you mentioned upgrade, am assuming you mean upgrade from Mk1 to Mk2 or Mk3?

If that is the case, you would be better off selling your amp and buying a Mk2 or Mk3 on the used market. You would never get the return on the money spent upgrading your Mk1 to a Mk2 or 3.

I have both a Mk1 and Mk2. Have heard the Mk3, but do not own one.

The newer ARC gear seems to have less of that tube sound.

would suggest the following with your Mk1 amp; try a set of Shuguang Nature sound KT-88s in the amp you currently have and bias the amp for the tubes. Think you'll be surprised at the sonic improvement over the stock ARC tubes.

best