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Post by steamroller on May 14, 2023 16:42:15 GMT -7
I think I read or heard somewhere, that power tubes "in the medium range" were a best choice for the Dr.Z amps. What does that mean? What is a low/medium/high range? Is this a current measurement?
-steamroller-
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Post by wubberdubber on May 15, 2023 14:54:19 GMT -7
I don't think it means much at all.
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Post by adam on May 15, 2023 18:20:32 GMT -7
I don't think it means much at all either. I think when Mike refers to that, he's mentioning that if you have a cathode biased amp, any middle of the road output tubes will work fine.
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Post by scottyc13 on May 16, 2023 18:52:19 GMT -7
I think I read or heard somewhere, that power tubes "in the medium range" were a best choice for the Dr.Z amps. What does that mean? What is a low/medium/high range? Is this a current measurement? -steamroller- It’s the current measurement that is done during testing. The guys at Eurotubes gave me the explanation below. I ordered a matched set for an amp I built. So Dr Z is recommending something in the middle of the range say 30-34 mA. The cathode bias resistor in a cathode bias amp sets the idle current of the tube. Too high or too low a current rating of the tube will sound different than center line because the tube could be running warm or cool of it’s target. ”Well yes, that is what those numbers are. They represent 33 and 31 mA respectively. We use the book spec from the datasheet and a real world voltage you might see in an amplifier. In the case of a 6V6, 450V on the plate and 40V on the screen. You are correct, at 2mA apart you won’t hear much difference. In a cathode biased amp, they will be nearly identical. Ideally, any grade will sound the same if your bias is the same. You can take anything from a grade #26 to a grade #38 or even more and bias them up to have the same idle current and they will all sound the same. There are a few caveats with this. If you have a tube that is very cool in a fixed bias amp, that does not require much bias voltage, then that could limit your headroom, but this is very unlikely in most designs. If you have an adjustable bias amp, you can probably understand that 70% of peak plate dissipation is a great region to be in for good power, good tube life, and good tone. You can experiment with the bias, and say try things between 65% and 80%. The cooler end will give you more clean headroom, up to a point, too far and you’ll get into heavier crossover distortion. And the warmer end will have earlier breakup on the volume knob, too far and you can risk over-dissipation and shorter tube life. That’s about all there is to it.” I highly recommend Eurotubes as a supplier. They’re in Oregon.
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Post by steamroller on May 18, 2023 18:20:27 GMT -7
I really appreciate the responses, I am currently replacing my power tubes. More importantly to tube replacement, I need to purchase a set or two to have on hand. Dr.Z explained in one of my enquiries, that when you change tubes, an amp can sound different. He said it usually is a minor concern. I don't have golden ears, but I don't want replace tubes in a manner that will guarantee a significant change in the sound of my Z-Plus! I am mostly concerned with the way the amp responds to changes in pick attack and volume setting changes, I guess everything else too! This is my first amp forgive me!
-steamroller-
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Post by scottyc13 on May 18, 2023 18:32:14 GMT -7
Even tubes in the medium range from different manufacturers can sound a little bit different. The Z Plus is a single ended amp. I would recommend trying maybe a NOS 6V6 and a current production 6V6 to start. I like the JJ 6V6 in amps I’ve built, but those are my preferences. There are a few sites like KNOS tubes that have NOS tubes. There are also current production 6V6 to try from sites like the Tube Store. Pick a couple out and give them a try. Tell us what you find out.
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