I have stripped down an old St70 and am doing a complete mod on it, using the Curcio 4-tube driver circuit and regulated PSU. I've also got 4 new EL34 marked "National Electronics" and "made in China". Does anyone here have experience of these tubes or this manufacturer? I got them cheap so I am not expecting too much....
Another question: How important is it to match output tubes on the ST70
Thanks / Michael
Another question: How important is it to match output tubes on the ST70
Thanks / Michael
I've also got 4 new EL34 marked "National Electronics" and "made in China". Does anyone here have experience of these tubes or this manufacturer?
National manufactures no tubes. They only re-brand whatever is cheapest that week. In your case, it was Chinese tubes, probably Shuguangs. Is there any type of Chinese tube other than Shuguang?
How important is it to match output tubes on the ST70
Michael,
It's quite important that each pair be well matched for both gm and cathode current. A Dyna ST70 has a bias adjustment for each channel, not for each tube.
Perhaps I should incorporate a bias adjustment for each tube. I guess it is only a matter of having a separate cathode resistor and a separate bias source/pot for each tube? I was thinking of reducing the cathode resistor to about 1 - 2 ohms instead of the current 15.6 ohms
Perhaps I should incorporate a bias adjustment for each tube. I guess it is only a matter of having a separate cathode resistor and a separate bias source/pot for each tube? I was thinking of reducing the cathode resistor to about 1 - 2 ohms instead of the current 15.6 ohms
Yes, that's a very good idea. Reasonably well-matched tubes is a good start but having the means to adjust them individually is also good.
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