6K5GT & EL36 AMP

[alexkhar]

Hello everybody!
Let me share scheme of my last amp. 6k5gt in driver and EL36 such out tube. TDH about 1.1%. Range 20H...22kH. Power about 1.8Wt for channel. Sounds excellent! Link to the video.

 

[celestar32]

I like the music. What is the title of the song?

 

[alexkhar]

The greatest hit from famous Russian singer Boris Grebenschikov. The name of the group is Aquarium. The name of the song is Silver My Lord Giveth Me. I really enjoy it too.

 

[MrCurwen]

Your tubes have really nice looking hats! Nice to see different top caps than the white ceramic ones.

 

[alexkhar]

Right you are! Firstly I have made my amp using white ceramics caps. But it looks like poor usual device. Then I changed it.

 

[rcollege]

Very well done! It sounds very nice!
Why did you choose the 6K5GT?
I love the 6K5GT... its good to see someone else using them!
I like the wood work as well.

 

[alexkhar]

I started with Russan 6F5M. Then I tried to use Mullard 6F5. And on the one Russian forum I read about 6K5GT. I stoped on 6K5GT in high voltage mode (more than 400V). Sounds great! I recomend to use 65KGT in high voltage mode with amperage about 1.1mA and load resistor from 180kOm to 220 kOm. Sorry for my poor English. I have just started to stady it.

 

[costis_n]

Alexei, I think you know what you are doing. Bravo!
How did you make the top caps?

 

[Palustris]

I just built an amp using the 6K5 to drive a JJ 2A3-40. Mine is direct coupled with a CCS set at 1.3mA as a plate load for the 6K5. I used a 3k ohm cathode resistor on the 2A3 to bring the grid up to 155V which is, naturally, the plate voltage of the 6K5. The plate voltage of the 2A3-40 is 300V and the bias -65V. B+ is just over 500V.

 

[alexkhar]

Alexei, I think you know what you are doing. Bravo!
How did you make the top caps?

I have bought their on eBay. Example.

 

[alexkhar]

I just built an amp using the 6K5 to drive a JJ 2A3-40. Mine is direct coupled with a CCS set at 1.3mA as a plate load for the 6K5. I used a 3k ohm cathode resistor on the 2A3 to bring the grid up to 155V which is, naturally, the plate voltage of the 6K5. The plate voltage of the 2A3-40 is 300V and the bias -65V. B+ is just over 500V.

What about characteristic? TDH, Power? Could you show circuit?

 

[Palustris]

I'm traveling for the next 6 weeks so don't have access to my desktop computer with all the info on it.

The 2A3-40 is biased at Ep = 300V, Ip = 65mA, Eg = -65V; the 6K5 Ep = 155V, Ip = 1.3mA, Eg = -1.3V. Plate load for the 6K5 is cascoded mosfets. Power out was 3.5W at 1% - 2% THD. 2A3 grid current was the determining factor with respect to power out as it occurred at about -60V. Overall power supply B+ is just over 500V. As I said above, the 6K5 is direct coupled to the 2A3 grid by using a large cathode resistor composed of a two resistor voltage divider (bypassed to the B+). The voltage divider uses the upper resistor to set the bias for the 2A3. The lower resistor sets the plate voltage for the 6K5.

For a 300B I think the B+ would have to be ~600V and the driver would have to be changed to a 6F5 and a source follower employed.

The amplifier is extremely clean with highly detailed sound. I am very impressed with the sound as I have always used a high transconductance triode or triode connected pentode in the past to drive a 2A3. These 6K5s have the cylindrical plates that make the 6F8 and Tungsol 6SN7 tubes so popular. Maybe there is something special about this tube construction.

 

[alexkhar]

Thank you for huge information. Could you show the circuit of your Amp?

 

[Palustris]

Sorry, I only have my laptop with me. The schematics are on my desktop computer.

 

[Palustris]

I'm sorry that my description of the circuit above was wrong: I conflated two different amps: the 6K5 driver with the E180F (T) driver. So, I thought I would draw out the schematic since it is so simple. Naturally this is without power supply and details of the CCS. You can replace the variable 1k ceramic power resistor and the 2k ohm fixed resistor with a single fixed resistor once you get the whole thing dialed in properly. Note that I forgot to draw in the wiper of the 50r pot that connects to the cathode resistor.

 

[alexkhar]

Thank you very much! I didn't find capasitor between 6k5 and 2A3. Is it absent? Or you have forgotten draw it?

 

[Palustris]

There is no capacitor because the plate of the 6K5 is the same voltage as the grid of the 2A3; that's why I said it was direct coupled. I omitted the capacitor between the cathode of the 2A3 and the B+.

 

[rcollege]

I used the 6K5GT to replace the 6F5 on this amp.
http://www.diyaudio.com/forums/tubes-valves/281314-new-build-geraldine-se-amp.html

The best sound comes from the 6K5GT driving the 6L6GC
The 6K5GT ends up at around 250V from plate to cathode. Sounds good...fuller than a 6J5.... and cleaner than the 6F5. It really has good bass, keeps the highs and good clarity.

Off to buy more before they catch on.