Audio Research VS 115 bias Adjustments

Well..see my comments above. Those sonic changes were due to the KT-120. I can only assume it will sound the same in your amp. G

First off, KT-120's are not available yet through ARC for re-tubing. They are only available for new production. Hopefully this will change in the next few months. If you are concerned about some of your output tubes getting up into the 70mV range you can always turn the main bias pot down to 61-63 instead of 65mV. That wont hurt anything, and should not effect tonality or distortion.

The KT-120's I saw from ARC did not have the Winged "C" logo on the tube. Instead, they were branded Tung Sol. They bias the same as the 6550. However, this tube does pull more heater current. That shouldn't be a problem for ARC amps unless the cage wont fit because of the tubes. That can be a problem with early ARC product. Caution may need to be taken if using this tube in a Dynaco MKlll, for example as it could make the transformer run very hot. I have not tried them in that amp however. In addition, those ARC amps that use a 6550 regulator in the power supply, that tube must remain. At this point KT-120's are not being used for the regulator tube.

Bifwynne,

I'm on the phone with ARC 2-3 times a week lol. Remember the KT-120 is a new tube so as info. becomes available it will be disseminated. If I hear anything, I will let you know. Happy New Year to you as well.

geek

6550, I service ARC equip.

Bifwynne,

The problem is, all ARC tubes are matched for current draw so that all tubes draw the same current. Also the ARC tubes that I use are run for 24 hrs. at bias to cull out the bad ones and to make sure the tube won't majorly drift over time after you install them. One more very important point, if an ARC tube ever goes bad within the first 60 or 90 days, I don't remember off the top of my head, the damage is covered by ARC. If you buy your tubes elsewhere you are on your own. I would wait till ARC makes them available. You can contact me if you wish. I don't want to make this an advertisement for my business as I don't have that type of account. gary.mf1@gmail.com. Hopefully the admin won't mind a private email. G

No I haven't personally however I have received feedback from people I trust. It's great! It should be understood that ARC listens to the tubes for a long time as well as life tests the tubes before they give their ok. If the tube sounded bad, they wouldn't be using it in their products. Your going to get a bit more slam and impact with the KT-120 and not in a bad way. It has an effortless quality. Very musical. The funny thing is I remember my old Dyna MK III's with the tung sol 6550 Coke Bottle tubes in them, and they were awesome. More slam, more impact w/o sacrificing any detail. By more slam I mean better transient impact. I think it's going to be a win win but only time will tell. G

Tomj2617. Awesome. they will take approx. 20 hrs. to break in so they should only get better over time. No need to run the amp non stop for 20hrs. however. Enjoy

Bifynne...I have a strong bias for buying from ARC? Awesome pun! LOL

I normally run the tubes at 50mV after 20 mins. to warm them up. After 45 mins I set them to 65mV. I do this while the line voltage is adjusted to 120Vac with the use of a Variac. This step is somewhat important as line voltage fluctuations can raise or lower the bias voltage by a few mV's. Since the factory does that, I do too.