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Vintage threads from the first ten years

tube matching

1/30/1998 11:00 AM
Chris	tube matching Is it possible to match power tubes while in the amp with a DMM?

1/30/1998 12:10 PM
R.G.	Yes, if you want to match only the DC bias of the tubes. You can put tubes in, measure the bias current in each tube, and repeat with different tubes until you find two that match. Read the >Tube" target="_blank">http://www.eden.com/~keen">>Tube Amp FAQ for how to do biasing. The process is the same, you just don't adjust the bias voltage, only measure the current. This will not match AC characteristics, only DC bias points. As the TAF notes, you can mod your amp to bias each tube separately and acheive the same effect as searching for DC matched tubes. As for AC matching, this can't successfully be done with only a DMM, I don't think. You CAN also modify the phase inverter to change the amount of AC available to each power tube to balance any two tubes for AC gain as well, but the simplest way to do this requires an oscilloscope.

1/30/1998 12:10 PM

R.G.

Yes, if you want to match only the DC bias of the tubes. You can put tubes in, measure the bias current in each tube, and repeat with different tubes until you find two that match. Read the >Tube" target="_blank">http://www.eden.com/~keen">>Tube Amp FAQ for how to do biasing.

The process is the same, you just don't adjust the bias voltage, only measure the current.

This will not match AC characteristics, only DC bias points.

As the TAF notes, you can mod your amp to bias each tube separately and acheive the same effect as searching for DC matched tubes.

As for AC matching, this can't successfully be done with only a DMM, I don't think. You CAN also modify the phase inverter to change the amount of AC available to each power tube to balance any two tubes for AC gain as well, but the simplest way to do this requires an oscilloscope.

1/31/1998 5:27 PM
GVB	I've never really considered matching the AC bias in a guitar amp. Since I've never used AC matched tubes before, I don't know the effect on the signal/sound of the amp. I would suspect that unlesst the tubes are way off, It wouldn't make much difference to my ears. What are the effects? I may consider experimenting with this, but I would like to know how worthwhile it is. It's probably better left to the HI-FI people, but its and interesting point. GVB

1/31/1998 5:27 PM

GVB

I've never really considered matching the AC bias in a guitar amp. Since I've never used AC matched tubes before, I don't know the effect on the signal/sound of the amp. I would suspect that unlesst the tubes are way off, It wouldn't make much difference to my ears. What are the effects? I may consider experimenting with this, but I would like to know how worthwhile it is. It's probably better left to the HI-FI people, but its and interesting point.

GVB

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