ARC ref 110 tube bias prob

willmarchant

... the tube I had in place when the resistor blew, I’d moved to another position as a slave tube ...

Why? It's guaranteed to fail again, sooner rather than later.

The ARC resistors are out of stock in Europe and UK (62 weeks before they’re going to be available!) so I’ve used an equivalent temporary resistor from another manufacturer. And bingo, it’s fixed the weird bias readings I had.

Minor difficulty - the tube I had in place when the resistor blew, I’d moved to another position as a slave tube. The slave tubes are supposed to be in a voltage range of 58-73mVDC but this one measures 52.8mVDC.  All other master tubes are at 65mVDC and the other slaves are in the right range but this one isn’t.

Does this matter? Does it affect the sound much? Will it cause other problems - can I live with it or do I need to replace?

Thanks

@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!

Think I’ve found the problem!

All the brown resistors adjacent to the bias testing points were showing c. 1.3-1.5 ohms but the one adjacent to the bias for the tube that gave crazy readings was showing nothing. No continuity, so assume it’s blown? I’m not an electronics guy but is a resistor like a fuse - a piece of wire that can melt/break?

It looks easy enough to solder on a replacement. I’ll call the UK technical team tomorrow but do you think this alone could be the problem? As far as i can tell the other resistors look fine. Don’t know how to check a capacitor but perhaps i dont need to?

shame this forum doesn’t easily allow photos!

that comment by the op caught my eye too.... 

@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.)

Thanks all. I called ARC yesterday and they are due to come back to me later. They asked me to check if the resistors nearest the last tubes looked burned out but they look fine. With the new tubes in the ref 3 and this 110 it sounds fantastic - cant believe what I’ve been missing but I guess there’s a problem I need to fix. I’m waiting to hear from ARC whether I’ll cause damage by using it like this.
In the UK I only have to take it 40 mins up the road to the UK importer but fear they’ll have it for weeks!

Not sure its something I should try and fix myself. 

@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)?

Yeah, I know I lent you my 2 cents in your original thread but I was wrong. I think only a circuit problem like the above referenced resistor could explain your Fluke reading. 

i have that amp, is that particular one new to you?

seems like when the last set of power tubes went (perhaps in the hands of the prior owner), they took out a biasing resistor in that quadrant, which will likely require the amp traveling back to minnesota

I would call audio research. In the past I have done this and talked with… the tech. Or email. But calling is quicker.