Audio Research VT100 Mk1, Mk3; VS115

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.

@richardp01

Are you 100% sure you have everything adjusted correctly?

I ran across an old Agon thread that may be of interest.

Quote from thread.

-> there is another measurement that you should check (before the power tubes are in) and that is only listed on the actual schematic. It refers to the grid #1 bias. If it as MUCH more positive, say -30 or -20 vdc, then you put that tube in a condition for excessive bias current. Since you blew both the 1 ohm plate resistor and the 100 ohm grid #2 resistors and the traces under the resistors that tube was either put in that state by excessive positive bias on pin 5, and/or it was faulty and simply arced and took everything out (likely the case since you dialed in the input tubes so well)

https://forum.audiogon.com/discussions/audio-research-vt100-mkii-retubing-blew-resistors

Jea48,
Thanks for your concern.  I seem to be blessed with regards to my VT100.  I ran it for a month on new input and driver tubes without even checking the bias.  When I did do the biasing I found the 160 volt measuring points to be within the specified tolerance of +/- 20 volts of 160 volts and 20 volts of each other before I began to adjust anything and they remained that way after all was done. So I didn't have to swap the tubes around willy nilly. The tubes I ordered were not matched but the two sections were very close to each other for each tube.  It took me over 2 hours of iterations on the resister pots to get everything within spec.  I didn't measure any points not mentioned in the biasing instructions.  After I biased the power tubes I went back and checked the voltages for the input and driver tubes again.  The 60 volt points had drifted to 61.5 v.  I turned them down with just one pot in each channel and the other voltages stayed within tolerance.  I finally checked the power tube biases again.  You can see why it took such a long time.

In spite of everything being within tolerance things can still fail.  That is not only the nature of tube equipment but virtually any machine created by man.  Tube gear just fails more frequently.  I bought the amp 6 years ago and it is at least 20 years old.  I figure I've had a good run with it.  If something fails before I sell it I'm prepared to spend some addition money to replace it.

According to Alice Trillin, wife of famous humorist Calvin Trillin, “Money not spent on a luxury once considered briefly is the equivalent of a windfall income and should be spent accordingly.”  I'm in her camp.