What Audio Research power amps have you owned or admired?

[jadis]

HI jadis,
Maybe the idea that a direct air flow on the tubes is bad has merit but my D250 does not seem to suffer problems. The four fans are horizontally mounted at the very bottom of the chassis and blows air directly vertically. They constitute a nearly continuous fan surface almost the size of the bottom of the chassis.

Sparky

Hi Sparky,

In your D250, that answers my question as now I hear a case where the fans, though not high powered, are blowing directly upwards against the tubes, as opposed to blowing downwards which will have an exhaust fan effect throwing the heat downwards. Thanks for sharing.

[yern]

http://www.maximatcher.com/maximatcher.html

The maximatcher is a modern output tube tester.

I have an ARC D70 Mk II, I biased it myself, based on the owner's manual. This is the first time I've biased a tube amp. I've never done it before. The trick is to get to the test points easily. With the amp off, I used minigrabbers to access the TP pairs.

[Steve Williams]

http://www.maximatcher.com/maximatcher.html

The maximatcher is a modern output tube tester.

I have an ARC D70 Mk II, I biased it myself, based on the owner's manual. This is the first time I've biased a tube amp. I've never done it before. The trick is to get to the test points easily. With the amp off, I used minigrabbers to access the TP pairs.

It's a $600 investment. How accurate are they at that price

[yern]

It's a $600 investment. How accurate are they at that price

No idea, I just found that site and references to it when I was searching on-line for output tube testers.

[MylesBAstor]

It's a $600 investment. How accurate are they at that price

Measurement Functions Plate Current (Ip) Range: 0 to 120.0 mA DC, ± 1.5 %
Transconductance (Gm) Range: 0 to 19.99 millimhos,
± 1.5 %

I don't think there's anything current that is more accurate other than the Amplitrex. Old testers always need to be calibrated and don't work at real world voltages.

Thing is, most tubes need a 48 hr burn in before testing and optimally, should be tested in the circuit being used. But if you're using NOS tubes, that's not an option; in addition, if you use something like a cj amp (unlike say VTL), there's no way of telling which output tube failed when the protective fuse blows (unless you're lucky enough to see which tube goes cherry red).