There are several things I don't know about 6n6p and have to experiment with, as follow : may be supplied safe at 400-420 V around ? what is its heater to cathode voltage limit ? In actual configuration with 200v into cathode the heaters are elevated at +100v around which in respect with the tubes I tested ( ecc82, 12au7, 12bh7, ecc99) get enough room to be used into specs. Not sure about 6n6p please.
catalin gramada,
Is your schematic accurate?
I have a few questions:
Many NE tubes ionize at 90V, and then settle in to 60V.
That does not protect the 12BH7 grid.
Why is the negative grid bias voltage supply - 58V, that powers the 6V6 tubes voltage divider bias adjustment?
Why are you using a Push Pull output transformer instead of a Single Ended output transformer?
It does not give decent performance for Hi Fi Stereo.
Is your schematic accurate?
I have a few questions:
Many NE tubes ionize at 90V, and then settle in to 60V.
That does not protect the 12BH7 grid.
Why is the negative grid bias voltage supply - 58V, that powers the 6V6 tubes voltage divider bias adjustment?
Why are you using a Push Pull output transformer instead of a Single Ended output transformer?
It does not give decent performance for Hi Fi Stereo.
Hey
Yes the schematic is pretty accurate : 6sl7 floating paraphase inverter direct coupled to cf ecc99 grids into a shared 470nF/47k rc pole for 3 paralleled output tubes per side..
It was a pentode p-p 6l6gc / el34 project. Triode connected is something I want to try. I don't know if the ecc99 cf driver I have is proper to drive 3 parallel 6l6 triode connected, right now it works with 11mA to each side the output impedance should be a couple of hundred ohms order.
I rolled different tubes in as 6l6gc/ 6p3s /el34 -48v was the bias voltage used with the 6l6 for 30 mA at 450v around.
I have ecc99 right now as cf drivers. I didn't know the Ne didn't protect the grids at cold start up - I will replace with o diode thanks
Yes the schematic is pretty accurate : 6sl7 floating paraphase inverter direct coupled to cf ecc99 grids into a shared 470nF/47k rc pole for 3 paralleled output tubes per side..
It was a pentode p-p 6l6gc / el34 project. Triode connected is something I want to try. I don't know if the ecc99 cf driver I have is proper to drive 3 parallel 6l6 triode connected, right now it works with 11mA to each side the output impedance should be a couple of hundred ohms order.
I rolled different tubes in as 6l6gc/ 6p3s /el34 -48v was the bias voltage used with the 6l6 for 30 mA at 450v around.
I have ecc99 right now as cf drivers. I didn't know the Ne didn't protect the grids at cold start up - I will replace with o diode thanks
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Paralleled SE tubes should be cathode biased to force current sharing.
SE is not recommended at all for SE operation, paralleled tubes or otherwise.
There is not a SE but a P-P circuit using 6 x 6l6gc triode connected. The current is well balanced in output set. Each equally draw 48 mA at 440V for max 21 Vpk into 4 ohm load. 1.9k pp OT used. My actual question regard the driver I should use for ? Just for now I used an ecc99 as cathode follower suplied at 400v with 18k in cathode. It sound well but changing resistor to 10k make a huge difference. 10k in cathode meant 20 mA DC so 4w dissipate per tube section, way to much for 3.5w max specs. I expect now a 6n6p which is bigger power rated but who can tell me what make a good driver for my actual output configuration please ? Thanks.
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Obviously you're exploring class AB2.
That means driving power tubes into grid conduction by exceeding Vgk = 0.
As the grid input impedance becomes low with grid current, the PI driver must have low output impedance allowing for sufficient grid current.
The output impedance of a CF is 1/Gm.
So the higher Gm, the more grid drive will be available.
Without grid current (class AB1) a pair of 6L6GCs will give around 15W in triode mode.
In class AB2 this might be increased to about 20W per pair.
BTW, your square wave response looks about normal.
For a better response you would need a wider bandwidth.
A good square wave (SW) response requires the lower corner frequency of the amp to be at least 10 times lower than the SW frequency, while the upper corner frequency should be 10 times higher than the SW.
The bandwidth of your amp might be mainly limited by the OT.
If so, the only way to significantly increase the bandwidth of the amp would be global NFB.
That means driving power tubes into grid conduction by exceeding Vgk = 0.
As the grid input impedance becomes low with grid current, the PI driver must have low output impedance allowing for sufficient grid current.
The output impedance of a CF is 1/Gm.
So the higher Gm, the more grid drive will be available.
Without grid current (class AB1) a pair of 6L6GCs will give around 15W in triode mode.
In class AB2 this might be increased to about 20W per pair.
BTW, your square wave response looks about normal.
For a better response you would need a wider bandwidth.
A good square wave (SW) response requires the lower corner frequency of the amp to be at least 10 times lower than the SW frequency, while the upper corner frequency should be 10 times higher than the SW.
The bandwidth of your amp might be mainly limited by the OT.
If so, the only way to significantly increase the bandwidth of the amp would be global NFB.
catalin gramada,
Are you running the circuit in PP Class AB2?
I guess not, because you said AB1.
A cathode follower driver with RC coupling to the output tubes in Class AB2 does Not work properly.
A2 draws grid current, the C in RC charges up, and that causes a bias voltage shift on the output tubes.
After we all see the schematic of Post # 1 . . .
Now you tell us this is a Push Pull circuit (I should have guessed, you said AB1).
Even given the first facts, a complete and accurate schematic saves 10s or 100s of Posts, and 10s or 1000s of words.
Are you running the circuit in PP Class AB2?
I guess not, because you said AB1.
A cathode follower driver with RC coupling to the output tubes in Class AB2 does Not work properly.
A2 draws grid current, the C in RC charges up, and that causes a bias voltage shift on the output tubes.
After we all see the schematic of Post # 1 . . .
Now you tell us this is a Push Pull circuit (I should have guessed, you said AB1).
Even given the first facts, a complete and accurate schematic saves 10s or 100s of Posts, and 10s or 1000s of words.
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