Tube arch

Change the output tubes when the silver getter flash starts turning brown.

for arc tube amps and avoiding the ’destructive protection’ the op seeks to avoid, this is bad advice

In general Audio Research recommends changing/replacing output tubes in their amplifiers every 2000 hours. Assuming you have the owner’s manual, you should be able to confirm same. Another suggestion would be to periodically check the individual output tube bias.

this is good advice

i understand in the case of the op’s amplifier using sooo many output tubes, i would suggest perhaps stretching the hours to 2500, maybe 3000... but check biasing often... when certain tubes or pair/bank starts to ask for more bias, it is a sign they are getting closer to going bad

i would also advise the op to make sure the amp gets excellent ventilation -- big impact on tube life in my experience

@jjss49 +1. A tube tester is also not a bad idea.
The Ref 750 have 18 tubes KT150s and 1 6550 per amp right? That’s about $7,000 each time you re-tube both mono blocks, every 2000 hrs or so?

I have to ask. Are you sure you need all that power?

I had monster solid state amps for well over thirty years. It was clear that more power made a big difference in the overall sound quality. Overpowering was always good.

A few years ago I switched to tubes. Audio Research Reference 160m and 160s. They can be run in ultra linear mode with 140 wpc or in triode mode… 70 wpc. My Sonus Faber Amanti Traditional have an efficiency of 90db… 3db less than yours. I have found they sound better in triode mode (a touch more musical). So I run them in triode mode. There is no noticeable difference in volume between the two modes (yes, counterintuitive). I find with tubes the wpc is very little difference in sound unless you are really under powering, unlike solid state.

I listen to them in the 70db - 80db range at most usually. I had some youngsters over here to listen to them. They listened at way more… in the 90s. They sounded great… no loss of dynamics. Although I had to leave the room… I don’t like music that loud anymore. They were listening in triode mode (70wpc).

The new Audio Research Reference amps REF 80, Ref 160, and the new REF 320. Have automatic biasing. Also the tubes are slowly brought up to full power over three and a half minutes to increase tube life and prevent the power surge that can pop tubes and take out resistors. Tube life is three thousand hours… and retubing is only 8 power tubes in total.

Taken together, I would recommend you consider trading your amp for a REF 160s or REF 160m monoblocks. I have had both, the monos have a wider and deeper sound stage… the stereo has a bit greater impact.

tubegb

In general Audio Research recommends changing/replacing output tubes in their amplifiers every 2000 hours. Assuming you have the owner’s manual, you should be able to confirm same. Another suggestion would be to periodically check the individual output tube bias.

Audio Research recommends changing tubes every 2000 hours in their amplifiers that use KT120s and 6550WE (Ref 250 and Ref 75). With the newer amps (250SE, 75SE, 160M, 160S) running KT150s, the manual now recommends changing the KT150 every 3000 hours. The 2000 hour recommendation however still holds for the 250SE and 75SE that still have 6550WEs. The newer 160 series amps now have auto-biasing.

I’ll keep this short. So my last post was about a tube arc. Took out a resistor on one of my Audio Research Ref 750s. I replaced the resistor and put in a matching KT150. My question is how can I avoid this from happening again.

@tattooedtrackman I see what you did there a 'short' is why a tube arcs...

Anyway there is nothing you can do to actually avoid this but you do have good advice as to how to minimize it. The thing is, bad tubes gonna arc and age has nothing to do with it. Sometimes shipping is an influence and other times the tubes are simply bad and fail regardless. What I'm saying here is a tube might last 2 minutes or 2 years; there's not much way to know which, other than vetting the tube as best you can. 

ARC amps use a sacrificial resistor because if the resistor was rated to not fail, Bad Things would happen elsewhere in the amp that would be a lot more expensive to repair!

A fuse of course could solve the problem. They could be a lot easier to replace than a resistor. An LED could light to show the bad fuse...