My power amp ARC VT 100 keeps blowing tube

If you are in or near Cali. I can help you....

Sounds like a trip to the service center to me.

First off, I never use KT88's in ARC products. That being said, I'm guessing you have a problem underneath V16 tube socket, or the tube socket itself is bad. The problem is not necessarily setting the bias on VT100's, the issue is setting up the balance on the front end of that amp. It is not an easy thing to do. The input tubes must be matched and I only use ARC tubes. Replacing the input tubes without setting it up properly can shift the D.C. operating points thereby raising distortion and potentially causing issues.

As the power tubes burn in their bias will drift. The bias needs to be checked and ajusted for the first hundred hours or so. Even with tubes purchased from ARC. Power tubes change as they break in. After the burn in period the bias should remain pretty steady.

Setting the bias for the power tubes on the VT 100 is not that hard. The driver tubes are a bit more tricky. I owned that amp for a number of years and set the bias many times.

Hi Jea48

The 6922 tubes were replaced at the same time as the power tubes. So they only have 200 hours. All was biased 1 year ago by authorised agent of ARC

Dan, I'm sure Jea means well, but I have read that bias the VT100 is NOT for amatuers. The bias pots are dangerously close to some potential fatal high voltage rails.

In fact, I know one tube outlet that refuses to sell power tubes to owners of ARC VT 100 amps. No names please. I would call ARC and ask for the closest ARC authorized tech station and let that person take it from there.

Good luck.

When was the last time you replaced the 6922 Driver tubes?
The VT100 MK1 and MK2 are not so easy to bias.

Courtesy of Abe Collins
http://mycollins.net/audio/artube1.html
To start click on picture to begin biasing procedure. Click on next picture for next step and so on until biasing procedure is complete.
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