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Big disparity in 6v6 current draw...

Matt-o-caster

Silver Supporting Member
Messages
258
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

Member
Messages
297
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

Member
Messages
7,757
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

Member
Messages
30,202
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

Silver Supporting Member
Messages
258
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.
 




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