Here is an article to show how I designed my 6SN7 preamp with CCS based on DN2540N5 or IXCP10M45S D-MOS transistors. The article is an addition to my design which showed a 6SN7 tube in parallel connection. Here I will continue to develop the schematic. I will introduce a popular solution for a reliable constant current source.
The constant current source
Initially I settled on a current source based on this topology. This solution is relatedly easy to implement, however it requires more components. In comparison a current source based on DN2540N5 or IXCP10M45S is much easy on the parts count. It requires only one external resistor and that’s it. A good info on these devices is available in W. Jung’s Sources 101 Part 2. The current source looks like this:
Connecting the 6SN7 to DN2540N5 or IXCP10M45S
As I showed in my previous article this 6SN7 preamp is based on parallel connection. Each 6SN7 triode will run at approximately 6.5mA which means a total of 13mA for the constant current source. I’ve got a 10M45S on hand and that is what I’m using for this schematic. Since there is no clear formula to allow me to calculate the exact value of the current set resistor I will use the following graph:
In addition a P-spice model for IXYS IXCP10M90S is available online. I actually used this model and came at a resistor value on 220R for a plate current of 13mA for both 6SN7 triode sections.
The complete 6SN7 preamp schematic
So we arrive on the schematic for the actual preamp itself. For this project I decided to explore the design environment of KiCad so this one is created on this platform.
A PDF version with all the details is also available for download.
The 6SN7+DN2540N5, IXCP10M45S preamp PCB
I know that tube purist might find it inappropriate but I use a PCB for my project. The goal is to enclose everything in a slim elegant enclosure. Therefore I chose a PCB. The main design feature is to have a PCB that sits vertically in a case in order to keep a low-profile. The PCB measures 38 by 135 mm and fits perfectly in a very slim enclosure.
Gerber and drill files are available for download. Use JLCPCB or any other of your favorite PCB manufacturers to get the boards made for you. The 3D model of the octal socket is available for download at my GrabCAD page.
I have been browsing your blog and I find it very interesting, I am also working on a preamp project based on 6sn7. Right now I am learning to draw in KiCad, I hope to be able to make my own PCBs soon.
I really liked your blog, greetings from Spain!
What PCB software did you use to render that 3D image?
KiCad now has a built-in ray-tracing rendering option. It’s really simple.
Kicad, I see looks great! One question though… Why do you need a constant current source?
Hi, you can check out my previous post on this blog for some more info:
I would like to know how much power transformer and amp size. I’ve tried custom made your pub now and it looks interesting.
I like your design but I think it would be better if your board has an option for cascode CCS.
I just wonder what’s the purpose of the relay in this circuit?
this is the MUTE relay.
Have you sim the circuit using kicad?
I want to sim the circuit but cannot find the exsample for create tube spice model on kicad.
you need to use a third party simulation software for this. You can use Tina-TI(for example). It’s easy to import the model. Here’s an example:
* 6SN7GTB Triode ewb Model 8/96, Rev. 1.0 (fp)
* This model is provided “as is”, with no warranty of any kind,
* either expressed or implied, about the suitability or fitness
* of this model for any particular purpose. Use of this model
* shall be entirely at the user”s own risk.
* For a discussion about vacuum tube modeling please refer to:
* W. Marshall Leach, jr: “SPICE Models for Vacuum-Tube Amplifiers”;
* J. Audio Eng. Soc., Vol 43, No 3, March 1995.
* This model is valid for the following tubes:
* 6SN7GTB, ECC32, 6FQ7/6CG7, 5692;
* at the following conditions:
* Plate voltage : 0..450V
* Grid voltage : 0..-18V
* Cathode current: 0..30mA
* Connections: Plate
* | Grid
* | | Cathode
* | | |
*SUBCKT 6SN7GTB P G K
BE1 2 0 V=V(P,K)+20.43*V(G,K)
R1 2 0 1.0K
BGp P K i=10.89E-6*(pwr(V(2),1.5)+pwrs(V(2),1.5))/2
Cgk G K 2.4P
Cgp G P 4.0P
Cpk P K 0.7P
BE2 20 0 V=V(P2,K2)+20.43*V(G2,K2)
R2 20 0 1.0K
BGp2 P2 K2 i=10.89E-6*(pwr(V(20),1.5)+pwrs(V(20),1.5))/2
Cgk2 G2 K2 2.4P
Cgp2 G2 P2 4.0P
Cpk2 P2 K2 0.7P
very nice project.
My question is: why you are using 1R resistor called as RF1? What it the purpose of it?
Thanks a lot.