Big disparity in 6v6 current draw...

[Matt-o-caster]

I just got my Weber Bias Rite BR-2 and decided to bias my DRRI. I hooked up the factory GT power tubes (just to test my biasing skills) and was shocked by the readings. One of the tubes was drawing 19 mA (which was about as anticipated) but the other one was drawing 40 mA! Is this even possible? I would think something would sound "off" with that great of a disparity in current draw between the two tubes.

Next, I plugged in my Tung Sol RI 6v6GTs and they were matched perfectly (thanks to Mike @ KCA NOS tubes). The bias actually didn't need much adjustment; it only needed to be a touch hotter.

 

[skipm45]

I just got my Weber Bias Rite BR-2 and decided to bias my DRRI. I hooked up the factory GT power tubes (just to test my biasing skills) and was shocked by the readings. One of the tubes was drawing 19 mA (which was about as anticipated) but the other one was drawing 40 mA! Is this even possible? I would think something would sound "off" with that great of a disparity in current draw between the two tubes.

Next, I plugged in my Tung Sol RI 6v6GTs and they were matched perfectly (thanks to Mike @ KCA NOS tubes). The bias actually didn't need much adjustment; it only needed to be a touch hotter.

In my JTM45 clone I was shocked to find one KT66 running @42ma with the other at 28mA. The shocking part was how good it sounded...
Like you, a matched set cured all. The sonic difference...noticeable I guess. I'm sticking with matched tubes.

Skip
www.skipzcircuits.com

 

[jamison162]

So those Groove Tubes were stock? Or did you buy the amp used?
That's a big difference. More important, how are you liking those Tung-Sols? What designation were the GT's? "S", "R", "C"???

 

[Blue Strat]

Is it possible? Well, you saw it didn't you?

Yes, new (and NOS) power tubes can be as much as 30mA out of "match". If they were all matched you wouldn't have to ask for matched pairs.

Sure they sounded good. NO ONE can hear the difference between closely matched and, say, 10ma apart tubes. Even further apart can sound fine as long as you're not getting hum.

It's still a good idea to get matched tubes so they wear evenly, though.

 

[Matt-o-caster]

So those Groove Tubes were stock? Or did you buy the amp used?
That's a big difference. More important, how are you liking those Tung-Sols? What designation were the GT's? "S", "R", "C"???

Yep. I bought the amp new around 2002-2003.

I LOVE the Tung Sols. They sound fantastic.

The GTs simply say "GT-6v6" on them. They don't appear to bear any other designation.

 

[jamison162]

Yep. I bought the amp new around 2002-2003.

Gees, so those tubes were 6 yrs old....no wonder they read so far apart.
I bet putting those new Tung-Sols in was like getting a brand new amp. They are sweet.

 

[Matt-o-caster]

Yeah, the amp is 6 years old, but I've only put about 50-60 hours on it.

 

[jamison162]

Yeah, the amp is 6 years old, but I've only put about 50-60 hours on it.

Ah, ok.

 

[Matt-o-caster]

With the way it sounds now, I'll probably put than many hours on it in the next few weeks!