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In Reply to: RE: CCS for 6SN7 driver tube posted by DAK on June 20, 2016 at 12:15:36
I should have mentioned that the 6sn7 operating condition will be 320v B+ into a l00k plate resistor with the bias resistor of 390 ohms. There will also be a 100k plate to plate RH type or Schade feedback resistor from the kt88 to the driver tube. regards, Dak
Edits: 06/20/16 06/20/16Follow Ups:
It sounds as tho you are going to use one 6SN7 per output tube as a driver/voltage amp for each KT88 and you are going to split the phase with the Lundahl.Using both sides of each 6SN7 with say a 10M45 will definitely give you more voltage gain,but I'm not sure it will give you a enough.Keep in mind that you will have some losses thru the PS transformer because there is no gain before you split the phase and then you are asking a pair of low mu triodes to handle these duties.Now I see you mentioned in the post below that you are using 100K plate loads and that is set up for high gain..Were you planning on paralleling the triodes in each 6SN7,or using one triode for voltage gain and the other as a driver? I think you could do it the latter way.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 06/20/16
I was planning to use 1 half of each 6sn7 to drive each power tube. I realize that the 6sn7 has low gain and i could reconfigure the amp with a 6sl7 for more gain.
I have made this SE amp and really like the sound so i had the "clever" idea of making a PP version using the input transformer splitter.
It's too bad they don't have an octal version of a 7247 which is half of a 12AX7 and half of a 12AU7..You need to swing at least 100v of signal to drive the KT88s to full power.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
...is half of a 6SL7 plus half of a 6SN7, in one envelope. MFA Luminescence is the only commercial product that ever used them, so far as I know.
6EM7 is more like half 6SL7 and half 6BX7 with lower mu.
6DN7 is more like half 6SN7 and half 6BL7.
The high mu side of the 6EM7 is very like a 6SL7 half. The low mu side is quite different from a 6SN7 section. Its gm is `3x the 6SN7, mu about a quarter, and it is quite capable of use as the power final element.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Yes
I forgot about that.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
According to AK simulations the amp puts out 12 watts per channel. Which is decent. Really that is plenty for my speakers and the size of my room.
Now keep in mind that the HF=87 output transformers are in the 5k range where the typical KT88 runs at 3.3k to 3.6k. That will explain part of the lower power rating of the circuit especially if you running below 430v B+.
If that's all you are looking to get out of the amp which is 12 watts,your implementation would be fine.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
With what you're proposing to do, the Interstage transformer will be used in a parafeed arrangement which puts a cap in the signal cap. Also, it will be difficult to apply Schade feedback across the IT due to phase rotation issues (though you could probably add some local feedback between primary of IT and driver plate). If you were to just use the IT in 'series feed' as is usually done, then I would also suggest to look into a tube that is better suited for transformer drive, one with lower output impedance than the SN7.
Hi i am not using an interstage trans just an input trans to split the signal.
Sorry, my bad, I misunderstood. I guess the simplest CCS solution would be the IXYS 10M45. Another option could be two DN2540 mosfets in cascode and yet another option is the gyrator. Sorry but I don't have any specific circuits to provide you with. If you go the resistive loading option, Schade feedback would not be advisable since it lowers the input impedance of the driven tube and loads down the driver. Schade works well with pentodes since they act as current sources.
.
Here's the manufacturer's data sheet
http://ixdev.ixys.com/DataSheet/98704.pdf
Fig. 2 from the data sheet is what you will use to find the current sense resistor for a given current through the 6SN7. For example if you decide on 8 mA as the standing current for the driver, you'd use a 360 Ohm resistor on top of the tube.
Here's a design implementation as seen in Tubelab's SSE
http://www.tubelab.com/images/AssemblyManualSimpleSE/Simple_SE_Amp_Sch_11-08.jpg
Hope this helps.
If you want to use one with a diff amp, with plate resistors, for push pull you might want to use one in the common cathode (as current sink) instead of the resistor..
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/20/16
Correct, putting a CCS at the tail could be a good idea (although some would disagree) as it will force operation into class A for the driver and make this amplification stage a 'series' P-P amplifier.
Here's a cascoded pair of DN2540 mosfets for use at either the plates or the tail.
V1 is a 6N6P? It looks like a pentode in that schematic.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
.
Have Fun and Enjoy the Music
"Still Working the Problem"
The schematic i am following has plate to plate fb from the power tube to the driver. I am using a 100k resistor for that. I dont know if that will mess up the operation of this design.
Can you post your schematic?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No offense gents, I am looking for a tried implementation on a 6sn7 driver tube. I don't want to play with it as i am not all that comfortable using SS devices and invariably hook them up wrong. regards, Dak
Dak
How are you going to implement each 6SN7? Are you to use one of the triodes as a voltage amp and the other as a driver for each tube? You have to make up for the voltage gain you are losing in the earlier stage but not having any.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I am planning to use 1/2 of each 6sn7 for the driver so it will be a very simple 2 stage amplifier. I can also configure it with s 6sl7 driver tube.
Edits: 06/20/16
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