Matching tubes on the Audio Research VT 100 mk II

I have a vt100m2 too. Great amp. When it comes time to re-tube I do advise you to go to a tube good reseller like Kevin Deal of upscaleaudio.com. Audio research really overprices their tube sets imho. If you have a tube specialist in your area, that might be a good source as well since they can install them for you.

Installation and biasing are a fairly simple operation. There are a few detailed descriptions in the archives. If you like, you can email me and I'll help you out

Also, try the Svetlana KT88's. I put some of those in as an upgrade after using the stock 6550's for 500 hours or so. Definitely a nicer sound - warmer with better midrange.

In response to your question: The pairs of tubes in a VT-100 sit next to each other.

I am not sure of the "V" numbers, but the easy way to remember is:
When you look at the amp from the faceplate,
Left front 2 output (larger, on the top) tubes are a pair; Left rear output tubes are a pair; Right front 2 output tubes are a pair; Right rear 2 output tubes are a pair. You need to get at minimum matched pairs of 6550s, matched quads or Octets of tubes are even better.

When you bias them, the test points are the big grey resistor between the 2 pair on each side. The bias (value written on the circuit card). Be careful -- there is 460V running on the traces of the amp, and let the amp warm up for at least an hour before adjusting. Make sure the input is muted when doing the adjustment.

Some of the advise is good above, make sure you turn both bias adjustments to 1/4 of the value with the existing 6550s installed before new tubes are inserted. Failure to do so will most likely blow a screen resistor.

You can copy and paste the following link to view another audiophile's retubing of the Audio Research VT-100 mk. 2 amplifier (narrative and online digital photos):

http://mycollins.net/audio/artube1.html

Hope this helps.

Each side of the amp should get "matched quads" for the power tubes. You can buy matched quads from http://thetubestore.com Power tube rebiasing is quick and easy. Its a lot more involved for the driver tubes.