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Old 3rd December 2008, 07:02 PM   #11
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Its' not "bad" , just different, the 6SL7 is a high mu (Amplification factor), and can hold a lower anode voltage (Low power).
The 6SN7 is a lower mu (20 vs. 70) and can manage some 450 volts. You have to take into consideration these values when designing your amp. Like tearing thru anode curves like these.........Part of designing an amp circuit.
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Old 3rd December 2008, 07:19 PM   #12
pageboy is offline pageboy  United States
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That explains some of why the circuit needs to be redesigned. But what is the point of wanting to use a 6SN7 over a 6SL7? I'm guessing some subjective thoughts on the sound of high mu tubes or something? (You're talking to a very green noob here.)
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Old 3rd December 2008, 07:42 PM   #13
SHiFTY is offline SHiFTY  New Zealand
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You could always use the driver stage design from a typical 6SN7-300B circuit at slightly reduced voltage. Simply replace the 300B with a 2A3 and lower the voltage as reqd.

I have done this, the gain is a little high but otherwise it works fine.
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Old 3rd December 2008, 08:00 PM   #14
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Check this out.....................www.6SN7.com
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Old 4th December 2008, 06:05 PM   #15
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Quote:
Originally posted by pageboy
That explains some of why the circuit needs to be redesigned. But what is the point of wanting to use a 6SN7 over a 6SL7? I'm guessing some subjective thoughts on the sound of high mu tubes or something? (You're talking to a very green noob here.)
The 6SL7 was deliberately designed to have a very high Rp, both static and dynamic. It will easily operate with plate currents south of the 1.0mA mark, and its Pd(max)= 1000mW. That allows for large plate load resistors for high voltage gains without requiring high DC rail voltages.

Unforch, that makes for a VT that can drive Hi-Z, low C loads only. That doesn't describe the grid circuit of a 2A3 by any means. Trying to drive that with a 6SL7 would mean severe slew limiting since there won't be enough current to charge Ci + Cmiller + Cstray at the high end. When that 2A3 tries pulling grid current, a 6SL7 driver stage will just roll over and die. Those are some severe sonic compromises right there.

The 6SN7 isn't so limited, and it can pull quite a bit more current (6SN7GTB: Pd(max)= 5.0W) at the expense of less voltage amplification. It'll stand a much better chance of driving a 2A3. Although, I would use it as a cathode follower grid driver (active pull-up, passive pull-down -- which is what you need) as opposed to a grounded cathode (passive pull-up; active pull-down) for an even lower Z at the 2A3 grid, and better current sourcing capability. Whenever you see complaints about disappointing sonic performance from a DHT, look for inadequate grid drive.
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Old 4th December 2008, 06:37 PM   #16
pageboy is offline pageboy  United States
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Now that helps there. I appreciated the 6SN7 page, but this actually answers the question. Thanks.
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Old 4th December 2008, 10:51 PM   #17
jer3my is offline jer3my  Indonesia
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Thank you for that last explanation. Really helps understanding.
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