Audio Research VT100 Mk1, Mk3; VS115

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 

Jim,
I owe you a big chunk of gratitude for turning me on to that tutorial and scaring me into doing the bias adjustments to the VT100.  I just finished the procedure which indeed took about four hours.  I lucked out in that my new tubes did not have to be rotated to obtain the specified tolerance between the downstream voltages.  I won't bore you with all the details I just want to say I couldn't have done it without the tutorial.  The tutorial is for a Mark II and mine is a Mark I (actually, no mark) but I muddled through, locating the measuring points that changed between models.

For those who recommended against doing the biasing myself I will say your advice is well taken.  I know just enough about electronics to get myself into serious trouble although I've always managed to recover from my boo boo's.  One great piece of information I took from the tutorial was to attach alligator clips to my digital multimeter leads so that I didn't need three hands to do the adjustments and measurements.

I would chide the people at ARC into placing information in their manual about replacing the input tubes, even if it just says, "Don't try this at home."  They should also include the link to the above tutorial with their biasing instructions.  That would generate more maintenance business for them than they would lose when people get informed about the actual work involved in replacing tubes. Also it would be nice if they would reduce the number of screws holding down their equipment covers--twenty screws per panel--come on!


For everyone's information I replaced the power tubes about a year and a half ago at a cost of about $300 for NOS Winged C's.  (These are no longer available.)  I decided to replace the input tubes about a month ago at a cost of about $240 for EH 6922 gold pins selected for low noise and microphonics by Tube Depot.  The original tubes were just standard Electro Harmonics 6922's.  I found that the new tubes sound silkier than the old ones even without proper biasing.  It will be interesting to see if rebiasing caused any SQ change.

Thanks to all for your communications.

Rick

I just ran through my set of test tracks to check the new sound of the VT100 with proper biasing.  One is always uncertain in making comparisons without A-B switching but I detected less silkiness in the highs after properly biasing the input tubes.  Just a touch more sibilance in female voices.  Darn!  Maria Callas singing Norma is still quite acceptable; her crescendos are not too brittle.  Well not any more when compared to the old tubes.  The amp has a slightly more "tubey" sound with the proper biasing; and more than with the old tubes.  How does that work?  More highs and warmer midrange?

I plan to live with the unit for a while longer to get my money's worth out of the new tubes.  I'll probably go for a VS115 by the end of the year.