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In Reply to: RE: Thank You posted by Triode_Kingdom on November 28, 2015 at 15:32:05
Check out the article in Vacuum Tube Valley #16 on Dumpster Tubes: Vertical Output tubes. There is a good write up about all the tubes types in question.
The amp was checked out after re-wiring the filament supply for voltage and basic measurements.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Follow Ups:
I'm not sure what you're saying. Either you did or you didn't make distortion measurements. I don't really care one way or the other, I just wondered how you might see improved distortion characteristics with the 6BL7, when my own work indicates just the opposite.
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Buy Chinese. Bury freedom.
I'm saying that a quick and dirty check after re-wiring the filament supply, and following that with listening tests quickly confirmed what was very obvious. The sound from the speakers was noticeably improved across the board. Low level detail was significantly improved, and loud dynamics were much more open, without compression.Dave_Slage's measurements confirms that the 6BL7 CAN be as low or lower distortion than the 6/12SN7.
The reason that my application is/seems to be working better is that both my power amps are pentode, with separate screen supply/regulation. One set of amps is driving a quad of 1625 tubes, while the other set is driving a pair of 6883B tubes. The topology is (possibly) quite different from what you normally employ. I'm pretty sure the 6BL7 is driving the power tubes in a more efficient manner. My chosen speakers are ATC SCM19's (with a external outboard crossover). While they have some of the best drivers on the market, they need watts to sound their best. Ergo, high powered pentode amps.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 11/29/15 11/29/15
Is there some reason this is a touchy subject for you? All these replies, and you still haven't answered my simple yes/no question directly. OK, I get it now, you didn't make distortion measurements. You would have saved both of us some time if you had just said so at the beginning. Anyway, have fun with your amp, I'm glad it sounds better with the 'BL7s.
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Buy Chinese. Bury freedom.
Based on previous research, did not see the need to get a full set of distortion measurements after changing the driver tubes. IF there was an issue with the sonics, then yes, a full set of measurements would have been in order. The difference just from listening was significant for the better.
The VTV article written by John Atwood clearly states the 6BL7 in fact makes a great driver tube. I think the fact that the driver tube is driving a pair or a quad of output tubes helps the overall circuit performs better. The measurements earlier in this thread show the tubes distortion level between the 6BL7 and 6SN7 are very close.
Also thought this was worth bringing up because 6SN7's are getting rather pricey. While the 6SN7 may work better in some applications, in other applications, the 6BL7 may be a better choice.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
" The measurements earlier in this thread show the tubes distortion level between the 6BL7 and 6SN7 are very close. "
No measurements have been presented in this thread, only simulations. Real measurements say otherwise, and I'm not the only designer who has made them or reached this conclusion. Morgan Jones discussed this very thing in "Valve Amplifiers." The 6BL7 simply isn't as linear as the 6SN7, and your statement that "distortion was reduced by an order of magnitude" is highly unlikely to be true. That's why I asked if you had made a measurement. Of course, none of this means a 6BL7 can't be used to build a nice amp. For many uses, it's a highly underrated tube.
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Buy Chinese. Bury freedom.
Update...
I took a look at my tube models compared to the tube curves and neither were very close so I used curve captor to create more accurate models. Now I do get the SN7 being more linear. Where i was getting about 1% for each with the old models I now get .022% for the SN7 and 1.5% for the BL7 at the same conditions. Reducing the drive by a factor of 10 (+-6V out) gives .15% for the BL and .0012% for the SN7.
Here are the FFT's of the two signal levels.
It seems possible that the BL7 is adding some of that yummy SE distortion that PP amps quash.
dave
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Have Fun and Enjoy the Music
"Still Working the Problem"
A friend of mine has basically DIY amp as the one listed here in this thread. After hearing about the success with my amp, he changed his driver tubes from 12SN7 to 6BL7, and reported the same results. He is very happy with the results. He especially noticed a big improvement with low level playback. He also noted that it seems to have less distortion, cleaner midrange and treble.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
OK, I'll get around to measuring the amp. I am certain that the amp sounds better, with a much better noise floor, handles dynamics passages better (does not sound congested). I'm reasonably sure the amp will measure nicely as well.I don't doubt your measurements and real world experience. I also don't doubt that the 6BL7's are working better overall in my amps, and that the sound is cleaner (less distortion). Perhaps its a better match driving the power tubes.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 11/30/15 11/30/15
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