ARC ref 110 tube bias prob

@jjss49 , I used to have a pair of ARC VTM120s that would take out grid resistors on the CB enough that I got proficient at replacing them. Is this biasing resistor in a difficult location to get to, or might it be something that OP could de-solder & then solder a new one in (instead of shipping it back to Mn)?

@willmarchant  , I may be missing something, but that is interesting that you would have a tube with no bias reading but it would still sound good?

When my Cary amplifier went into a bizarre biasing mode on one channel, one of the things I was advised (not by Cary) to do was to take my MM and take readings on everything in the chassis and see if anything was wildly different than it's partner.  Can you get your probes on those resistors that ARC was referring to?

(On mine, my MM identified a signal cap that read way different than the other three.  Under further advice (again, not from Cary) I bought a cap checker and confirmed that the cap was bad.  I replaced the cap, and to my surprise, but delight, that solved the bizarre biasing problem.  So I went ahead & replaced the other 3 caps.)

@willmarchant , to be clear, I was not suggesting your issue is cap related, I was only relating the method I used to troubleshoot my amp. But before I got to the caps I checked (most of) my resistors & all diodes. In case you ever need to, there should be a setting on your Fluke for caps, but I understand that a cap checker is more definitive (at least that’s what the guy on AA who was helping me troubleshoot my amp via emails told me) so I bought a cheap one from Amazon. However, and not to digress too far, if you do ever check your caps with any kind of meter, either give them a day or so to discharge or get a shunt to manually discharge them, or you will fry your meter.

Anyway, yes, I do think that the resistor that is showing 0 ohms is your problem, but I do not know enough about them to tell you how they work internally. I have no doubt that many on this board do, & I will keep my eyes peeled here so I can learn also.

When one of my ARC VTM 120s would blow a grid resistor, it was easy to know because it looked and sounded like a Lady Finger firecracker had gone off on the CB. I used to grit my teeth & cross my fingers when I turned those thing ’on.’ I had ARC send me a bunch (I think that they were 75k ohms, from memory) that I kept on hand. But that doesn’t mean, I don’t think, that they cannot fail less spectacularly.

The value of the resistor will be identified by it’s color and the stripes on it.

Good job on (probably) figuring that out!