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Tube Experts -- Help with Retubing AR amp

Although I've owned tube preamps for some time, I'm just getting into tube amps. I recently purchased a VT-100 Mk. II, and need some help.

Audio Research tells me that only they match tubes completely. They claim that their tubes are measured for transconductance and low grid current. They claim many of the large tube dealers don't do this, and that the high percentage of rejects AR sends back to Sovtek (6922) & Svetlana (6550) get sold to these guys.

I don't want to pay AR's outrageous prices, but I want to get some well-tested and matched tubes. Particularly, I want to put KT-88's in. Many guys recommend Svetlanas, although they seem to be twice the price of the Sovtek KT-88s.

Besides some tube recommendations on experience, who will provide closely matched tubes besides Audio Research? l don't believe many suppliers do more than simply do a quick burn and measure, and do not really measure the parameters AR claims to.

AR also stated that the input & driver 6922's they use are closely matched, triode to triode, and that this is necessary for the optimum sound from these sections. When I asked about whether I could replace the 6922's myself, they indicated that they could provide the information on doing this, but said it was quite complicated. Any VT100 owners know about this?

I would greatly appreciate any help you tube maven experts could provide. Thanks! And long live vacuum tubes -- nothing compares.....
kevziek
5 responses Add your response
abecollins
219 posts
 
I would recommend getting TWO sets of matched quads for the power tubes. I used Svetlana 6550C's in my VT100 MKII. For the driver tubes I chose JAN-Philips 7308 Low Noise. You need 8 driver tubes and I had 12 on hand to get a reasonably good match. Adjusting the power tube bias is very simple but the driver tube adjustments are a bit more involved. I bought all my tubes from http://thetubestore.com and had no issues but you will likely get better match quality from Kevin Deal at http://upscaleaudio.com. You can check out my website with more info and pics.

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

Good luck!
plugged
28 posts
 
Do NOT use KT-88's in your amp. The power supply won't be happy with the higher bias voltage they require and the layout isn't condusive to the extra heat. Call ARC and ask them if they recommend KT-88's in their amps.

As for a supplier, I second Kevin at Upscale. He actually measures and tests BETTER than ARC does and charges a fraction of the price they do.

Kevin
The Sound Broker
weiserb's avatar
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weiserb
476 posts
 
Setting the bias is not too dificult . You need an auto ranging multimeter from radio Shack < $ 50.00 and the plastic screwdrivers also from RS . ARC Tech will walk you through it.
questforsound
126 posts
 
hi

we sell the tesla kt-88 -- we sell them in a matched quad for $149.00 plus frt ..

check out our showcase on audiogon...
the are a wonderful sounding tube and yes they are trully matched at the factory ...These are the latest improved version direct from the Tesla Factory in Slovak Republic.

good listening
stephen
sc53
719 posts
 
Call Kevin at Upscale Audio for much better prices on all the ARC tubes you will need. He tests for everything ARC does, but go ahead and ask him for a detailed explanation. He sells all kinds of 6550's or KT-88's and of course all kinds of different 6922's. Website is www.upscaleaudio.com and make sure to phone not email for a fast response. One thing to remember: after you retube your ARC, you or someone will need to rebias the amp for the new tubes. When you send the amp to ARC for retubing, obviously they do this, but if you are going it alone, you will need to bias or have an ARC dealer or someone w/knowhow do it. I've never done it myself so I can't tell you how hard/easy it is. The VT100's are not self-biasing so it'll have to be done by someone.
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