ARC Quality Issues Ref75 Ref5SE Ref10

@Bifwynne, whilst the points that you make are known to me, however as there have been a sufficient number of instances reported where drift, or critical failure of bias resistors has occurred, and where the clock time on OPT's has past the initial phase where a weak tube may fail early and well within the usable life span of an KT120, For me, to reason, that a slight increase in current handling of the bias resistor, whilst remaining at the same ARC specification Ohmic value, may provide an increased margin of function, without compromising their additional role as a fail safe.

Tsushima1 ... your point is beyond my technical pay grade. Maybe Gary (Hifigeek1), Al (Almarg) or Ralph (Atmasphere) can explain why ARC uses bias resisters that handle only the rated wattage so chosen.

Again, from a non-techie perspective, I surmise that ARC is using low wattage bias resisters as a fuse and wants a quick "blo" to protect the rest of the circuitry if a tube arcs.

If I knew what I was doing with a soldering iron, I would do the repair myself. It's actually quite simple and low tech. Just clip out the burned resister, but leave a little stub sticking out if the board. Then soldier in the new resister to the stub of the old resister. Took the tech about 20 minutes start to finish.

The ARC tech also checked the other passives in the tube pair to make sure they were still in spec --- they were.

Tsushima1 ... this is NOT a big deal. You wanna own a tube amp ... it goes with the territory.

Btw, I understand from older threads that the reason ARC doesn't use circuit breaker type devices in the bias circuit is to limit the number of artifacts. Even still ... hard to believe that a fuse or circuit breaker in the bias circuit would make much of a difference in sound quality. But as I said ... this is above my technical pay grade.

Its common these days to use flameproof resistors in certain locations, usually the screen and cathode circuits), to prevent damage to the output transformer. If the tube conducts too hard, it can exceed the wattage limit of the resistor, causing it to fail just like a fuse.

Of course, why not just use a fuse, which has the advantage of being user-replaceable? There is the argument that a fuse might cause the circuit to not sound as good, but IME I've not seen that argument hold up in practice. Our Novacron amplifier has individual fuses for each power tube, and in studies we have done we don't find that the fuses or lack of them is any issue. But reliability certainly **is**.

Thanks Ralph .... sure wish ARC would get where you are.

Pushing a button or replacing a fuse makes a lot more sense to me than calling my local ARC tech. I am dubious that if ARC did blind testing on a "with and without" basis, that Bill Gehl, ARC's official listener, could tell the difference.

Oh well ... in the meantime, just glad the ARC repair guy is a short drive away.

Buy a Primaluna & be done with it. Euro design, premium Chinese build.
I never quite understood my buddies infatuation w/AR gear that would work
for a while then..... Big silver handles, big deal. Though I do like the early preamps, sharp edges and all, I wouldn't own one. Kinda the Chrysler of American audio. Nice motors but the rest is of questionable design build quality. You guys pretty much confirm what I've always suspected, a new
reference every 6 months...