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

Showing 3 responses by willmarchant

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. 

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!

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