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bugle boy tube bias blues and other tunes

Posted by Jonesy (A) on April 21, 2007 at 13:09:50

I was just starting to get the hang of leaving feedback to fellow inmates and dang... now I have issues!

I was doing some tube rolling in my Audio Research D70 driver positions V2 and V3, adjusting all bias positions and tweaking the output tube positions as well accordingly.

All going well, but when I put my original bugle boys back in V2 and V3, I now could not bring one of them down below 100 (where 90 v is the norm). (Unfortunately I did not check the bias readings before the swapping to see if it was out of whack already.)

I swapped V2 and V3 positions and the tube was still unable to come down in it's new position. The other trimmed well.

Okay, so maybe the tube was passed it's prime. But here's the deal. I had a spare set of bugle boys, one of those I could not bias down, and of the new dozen of (cheapies) 6922 Sovteks and 6DJ8 Sylvanias I keep around for the other spots as spares, 7 out of 12 I can't bring down below the mid 90 v's.

This took a long time to do, swapping positions, allowing settle in time, reversing positions, etc!

Is it just luck of the draw on the tubes, or is my bias circuitry probably getting out of controllable range?

Last night at 3:00 am I just about had with tubes! Luckily this morning my D70 just looked so good sitting there I'm giving it another chance!

Save me from solid state!

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