Audio Research REF 3 and REF 5 Tweaks

Covers on, covers off ... relatively minor differences and if you’ve not got a dedicated space with a guarantee of no one poking their fingers in then the cover is mandatory

On the two box models I’ve found that removing the cover on the signal tube section helps, likely the signal tubes are more sensitive to the extra vibration the cover might pick up and transmit

However on my one box Ref 2SE phono I find it works better with the cover on -- as others have observed this cover does tend to bow around the large and hot 6550 tube, not a great design

But while we’re talking tweaks you will get a much bigger impact from using better footers under your Ref series pieces -- the problem is that there’s not much real estate under the amp as the under plexi cover is pretty close to the front plate and stands proud. Putting feet under the plexi sounds awful - you need to anchor to the metal case that surrounds it. I get good results from Marigo Mystery feet but they need very careful placement -- part on the metal casework and the back of the footer (with a small attached boss) touching the plexi. Frankly once you get it right the effect of the feet is profound -- much more impact then fiddling with the top plates or the display

Oh and one other surprising realization.  Preventive tube changing is a great idea. I’d got about 2000 hours on my set of 6h30s in my Ref 40 but had an increasing sense that there was something a little off in the sound. A bit of tightness perhaps.  I was also suffering from odd (once every 3-4 sessions) channel drop outs. ARC say the amp should be good for 4000 hours on a set of tubes

As a new set of cryod tubes from Kevin Deal are not that expansive I decided to go for it - wow wish I’d done this sooner! It’s like a whole new amp.  Even at 20 hours in the sound is so much crisper and more open. I’d recommend all owners plan on swapping out every 1000-1500 hours or so, I think you can go longer on the power supply tubes

i half suspect that power up down may be as much an issue as absolute hours.  I tend to listen for shorter (1-2 hour) sessions so put the tubes through a lot of on and off cycles. With my Ref 2SE phono I needed to change at 500 hours. Anyway certainly if you listen for shorter times as I do don’t expect to get maximum tube life

Hmmmm, I'm not sure that's true. It's certainly not mentioned in any of the ARC owner's manuals that I've seen. It would also pose a potential shock hazard so it's a hard practice to recommend - even if some users with no children or pets do it anyway.

 I remember Leonard telling me many years ago that my preamp will sound better with the cover off. This was back when you could actually call ARC and talk to someone knowledgeable.

That won't happen with adequate ventilation. The plexi cover is a bit like the "canary in the coalmine."

 Yes it will. The top of the 6550 tube is extremely close to the Plexiglas cover. If you have the preamp on for long periods of time the top will melt. I usually listen for 4 or 5 hours at a time on the weekend. When I first got my Ref 5se it sat on the top shelf of my rack. There is a still a slight dip in my Plexi cover right where the 6550 sits. When I complained, ARC sent me a replacement metal cover. According to my dealer this was a very common problem.

My Brand new black ARC Ref 6 came in the other day and to my big surprise was the new twice as thick plexiglass cover that comes with the new 6s now. The front and 2 sides are beveled to making it very attractive also. It came with the smoked plexiglass with black screws prob because i bought the black 6. It will prob come with the clear cover if bought the natural silver finish. Anyway there is no way this new thick cover will dip from the heat. 

Ref5se

Tung Sol as noted by others in 6550 is a massive difference....Andy at Vintage Tube helped source mine

Ayre myrtlewood blocks under

i hear a slight change with display off. bigger change when I have DAC display off