Hi!
More than 6dB higher. Still low mu but in a range which makes a 2 stage amp possible when a step up input transformer is used
Maybe on paper. I don't like these tubes for driving large output tubes. I want a driver with oodles of headroom. The above suggestion has been proven and built it works nice and sounds great
Best regards
Thomas
More than 6dB higher. Still low mu but in a range which makes a 2 stage amp possible when a step up input transformer is used
Maybe on paper. I don't like these tubes for driving large output tubes. I want a driver with oodles of headroom. The above suggestion has been proven and built it works nice and sounds great
Best regards
Thomas
High gm triodes with CCS work also in practice. I have studied those a lot with real circuits.
By the way, have you ever tried such tubes as drivers ?
Hi!
I've used 6SN7, 6HS5, 417A, EC8020, 46, 801A and 211. Some in SRPP, mu-follower (with the same tubes and also asymetric with different tubes), RC coupled and transformer coupled. This was over many years, evaluation mainly by listening, with larger panel of people also. I do basic measurements but don't run extensive THD analysis.
Just sharing my experience. There are many differnet ways to build a good amp.
Thomas
I've used 6SN7, 6HS5, 417A, EC8020, 46, 801A and 211. Some in SRPP, mu-follower (with the same tubes and also asymetric with different tubes), RC coupled and transformer coupled. This was over many years, evaluation mainly by listening, with larger panel of people also. I do basic measurements but don't run extensive THD analysis.
Just sharing my experience. There are many differnet ways to build a good amp.
Thomas
Tubes of the 6SN7 or 5687 class make fine drivers running RC coupled from about 700 VDC, which is already available for the "50 watt" output tubes, class A1 only. Tie both halves in parallel, load resistor 25 K wirewound. Some folks like a triode connected EL84, with maybe a somewhat higher current, 25 or 30 mA (plate load of 10 to 12 K Ohm, big watts).
All good fortune,
Chris
All good fortune,
Chris
I've built a lot of high Gm tube in driver stage, ex 6s45p, 7788/ D3a/6J52P/6E5p/C3g in triode... these tube are so good.
Thomas,
what driver circuit makes you satisfied ? what are your speaker and your sound taste ?
How is the good ampli ? good for technical or listening ?
Many audiophiles in Japan do adjust their ampli by their ears, but without osciloscope. What do you think about this ?
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For me, Grid current/ driver current is important on sound quality (thin or thick/ soundstage/ dynamic...) in case of power tube in pure class A1.
A notion " slew rate current " for driver tube play significant role in circuit design. This notion maybe is relation to current of driver tube and current to grid of power tube.
With the same 2A3 output, so driver tube 12ax7, ef86, 12at7 (group of small current) will have big different sound compared to group of big current like 7788/ D3a/ C3g/ 6S45p/ 5842/ EC8010. When I take higher current for some driver tube, sound is not the same.
I'm not sure about formula of Slew rate current. Anyone could show me how to calculate it exactly ?
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Slew rate is a limit condition, far beyond linear operation. The ability is deliver grid current drive is a different thing, and for example is independent of frequency. Perhaps what you're getting at is the ability of the driver to charge and discharge Miller and stray capacitances linearly. To do this linearly leads us to the same "figure of merit" as high slew rate values, so the term gets used. But enough of that.
(Bearing in mind NASA's admonition about designing to a figure of merit) the calculation of slew limited output is voltage/time = current/capacitance. A nice simple linear function.
All good fortune,
Chris
Hi!
Yes these are good tubes, but I prefer them in phonostages, not as drivers for large triodes like the 211. These reason: I want more headromm than trhese can provide. I wrote an article about this on my blog:
VinylSavor: Gain, Headroom and Power
For ultimate amps were size, weight and cost is not a big issue I like directly heated drivers. For the 211 the 801A or a second 211 as driver. For cost optimized amps I settled for the 6HS5 as in the amp schematic which I linked before. My sound preferences are described in this article:
VinylSavor: How Does It Sound?
A good amplifier needs to satisfy my sound preferences. At the same time it needs to be technically solid and safe to operate.
Most important is the sound to the ear for me. But I do check the basic technical parameters by measurement. Just developing an amp by ear can lead you in the total wrong direction. Basic measurements are important to make sure the concept is correct and no wiring mistake has been done or to detect a faulty part
Best regards
Thomas
Yes these are good tubes, but I prefer them in phonostages, not as drivers for large triodes like the 211. These reason: I want more headromm than trhese can provide. I wrote an article about this on my blog:
VinylSavor: Gain, Headroom and Power
For ultimate amps were size, weight and cost is not a big issue I like directly heated drivers. For the 211 the 801A or a second 211 as driver. For cost optimized amps I settled for the 6HS5 as in the amp schematic which I linked before. My sound preferences are described in this article:
VinylSavor: How Does It Sound?
A good amplifier needs to satisfy my sound preferences. At the same time it needs to be technically solid and safe to operate.
Most important is the sound to the ear for me. But I do check the basic technical parameters by measurement. Just developing an amp by ear can lead you in the total wrong direction. Basic measurements are important to make sure the concept is correct and no wiring mistake has been done or to detect a faulty part
Best regards
Thomas
Hi Thomas,
Thank you for your reply.
Why do I consider your sound taste ? I think that taste is concerned to circuit design and kind of tube to get good sound. So far, I understand your philosophy
801A, 45, 2A3 are really exellent for driver stage cause of large headroom. But those are a bit... expensive, hard to find NOS tube and hard to treat DC filament. So EL34/ KT66 will be the choice. These can run over 400V with quite good headroom too.
Small tubes I mentioned above are fantastic for driver when the power tube requires 40-50Vpp.
Thank you for your reply.
Why do I consider your sound taste ? I think that taste is concerned to circuit design and kind of tube to get good sound. So far, I understand your philosophy
801A, 45, 2A3 are really exellent for driver stage cause of large headroom. But those are a bit... expensive, hard to find NOS tube and hard to treat DC filament. So EL34/ KT66 will be the choice. These can run over 400V with quite good headroom too.
Small tubes I mentioned above are fantastic for driver when the power tube requires 40-50Vpp.
Looking at the curves in the datasheet: http://www.drtube.com/datasheets/kt66-mov77.pdf
KT66 is nothing close to the linearity of the DHTs. Let's not even compare it to the 71A/45.
KT66 is nothing close to the linearity of the DHTs. Let's not even compare it to the 71A/45.
Hi!
These tubes are not that difficult to find and I also don't think that expensive if you consider the quality and lifetime you get from good NOS tubes, especially the 801A. A well implemented 211 amp is going to need expensive materials. If cost is an issue I would rather choose a different concept.
I agree with cotdt on the linearity. The directly heated triodes are more linear than triode strapped pentodes. The driver tube will influence the sound of the amp a lot.
I have seen such statements about triode strapped EL34 beeing more linear than DHTs a lot. it is simply not true.
Agree for such kind of drive voltages they are great
Best regards
Thomas
These tubes are not that difficult to find and I also don't think that expensive if you consider the quality and lifetime you get from good NOS tubes, especially the 801A. A well implemented 211 amp is going to need expensive materials. If cost is an issue I would rather choose a different concept.
I agree with cotdt on the linearity. The directly heated triodes are more linear than triode strapped pentodes. The driver tube will influence the sound of the amp a lot.
I have seen such statements about triode strapped EL34 beeing more linear than DHTs a lot. it is simply not true.
Agree for such kind of drive voltages they are great
Best regards
Thomas
I really like 6FD7 and 6EM7 for driver tube. I did build 2 amps with these tube. They sound great. Circuit: 1/2 first triode runs 1mA at 120-180K load, Vak about 110-120V, directly coupling to second triode; second one runs 20-25mA with IT 5k:5k; B+ is common to both triodes, about 300-320V.
Hi!
I believe this idea is based on a transformer having a 1000V secondary and not a voltage doubler on 500V, right?
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