ARC ref 110 tube bias prob


All is going well but the last two tubes (master and slave) are showing weird readings.

The master shows no reading and reading 16.76 volts DC (not 0.65mVDC!) on my Fluke. The slave is showing a negative rating (-20mVDC).

The tubes are all good (swapped them over) but any tubes in that position do the same.

Anyone know what’s going on?

willmarchant

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. 

@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)?

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. 

@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.)