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Old 8th April 2004, 11:14 PM   #1
Taffi is offline Taffi  Norway
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Thumbs up 6n7gt+300b

Hi!
I am not an expert in DIY, but have just modified a DIY amp to use 6N7GT(RCA/GEC) as input/driver and 300B(WE/GDmp) as ouput.
The amp itself are pretty heavy with a big outbord power supply.
Since I do not have a lot of knowledge on this subject I wondered if anyone could help me a little choosing the right voltages (and cap/resistors to get this).
I do have 100db+ speakers so I do not nead high gain.
Here are the schematic.
Click the image to open in full size.
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Old 9th April 2004, 01:29 AM   #2
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Hi,

You really have some odd values for the PS caps there....

91K Rin? Why not 100K and a 1K gridstopper iso 91K and 100R.

If you MUST use a 6SN7 in // then at least use separate cathode Rs for better current sharing between both sections of the valve.
So, 2 * 1K3 individually bypassed.

Why two 5U4s in /// A single one should do if the powerxformer can supply the voltage you need.

Cheers,
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Old 9th April 2004, 01:53 AM   #3
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6N7 != 6SN7

Plate voltage on the driver needs to be *much* lower. Closer to 120-150V. Decrease Rk or increase Rp...whatever keeps it in the linear range.

6N7 isn't really good for anything IMO because it has such low pervenace. 6SN7 is much better for a driver and probably more common. Given how much gain you need for this I'd suggest something resembling a 6DJ8. Maybe a 6SL7, although some people complain about slew rate or some crap like that. 6DJ8 really is perfect because it has the current capacity, but I can't think of anything octal that resembles it.

Tim
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Old 9th April 2004, 10:17 AM   #4
Taffi is offline Taffi  Norway
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Quote:
Originally posted by fdegrove

Why two 5U4s in /// A single one should do if the powerxformer can supply the voltage you need.

Cheers,
Only because this amp already are built like this and I see no reason to change it.
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Old 9th April 2004, 10:34 AM   #5
Taffi is offline Taffi  Norway
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Quote:
Plate voltage on the driver needs to be *much* lower. Closer to 120-150V. Decrease Rk or increase Rp...whatever keeps it in the linear range.
Thanks!
I do have to admit that I got a advice from someone else to DECREASE the Rp???
I also have a Heart Beat 300SE amp which use paralell-coupled 6SL7 insteed og 6N7 and that use 235V on the plate, but also have higher B+. Does the B+ voltage for the 300B be taken into account when deciding the operating points of the 6N7?
Quote:
6N7 isn't really good for anything IMO because it has such low pervenace.
Hope you are wrong
Quote:
6SN7 is much better for a driver and probably more common. Given how much gain you need for this I'd suggest something resembling a 6DJ8. Maybe a 6SL7, although some people complain about slew rate or some crap like that. 6DJ8 really is perfect because it has the current capacity, but I can't think of anything octal that resembles it.
As I told you I also have a Heart Beat that uses paralell-coupled 6SL7's as input/driver and think that amp sounds nice
Exept for a little less gain I do not understand that the 6N7 should be so much worse and a 6SN7 got ever less gain.
Please explain.
Thanks
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Old 9th April 2004, 11:52 AM   #6
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Hi Torfinn,

Welcome at DIYAUDIO!

If you want you can delete your double post by clicking on the edit button and then go to the delete checkbox and click on the delete button on the right...

Regards,
Bas

Ps...I did not know Rp meant plate resistor...I thought Rp was the plate resistance of the tube itself...I thought that getting a tube with a Lower Rp would be better....I am confused now..

Hopefully someone can clear this up for me.
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Old 9th April 2004, 02:58 PM   #7
Taffi is offline Taffi  Norway
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Thanks Bas!
Nice to be here
I suppose that it is me that has misunderstood the Rp question.

Regarding the use of the 6N7 I really gonna try it
And since as far as I can see the 6N7 has lower plate resistance than a parell coupled 6SL7 as used in the Heart (and as I like) I really can't understand why this not gonna work.

And since I like the Heart so much maybe I should try to use the same operating points as the Heart does, or?
Can I just copy the values from the Heart or is the 6N7 way different from the 6SL7 so I have to use total different resistors?

Click the image to open in full size.
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Old 9th April 2004, 03:16 PM   #8
grataku is offline grataku  United States
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Frank suggestion to split the loads seemed like a good idea.
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Old 9th April 2004, 03:34 PM   #9
Taffi is offline Taffi  Norway
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Maybe I have made myself unclear again.
The 6N7 has just one cathode.
The 6SL7 shown in the Heart schematics do have two seperate cathodes and also have seperate cathode resistors. It was just something I did not change in the schematic (I just modified the 6N7 schematic).
Was it this you meant?
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Old 9th April 2004, 04:39 PM   #10
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Hi,

Quote:
The 6N7 has just one cathode.
My mistake....I misread it and thought you had a 6SN7 there.

As you said, the cathodes of a 6N7 are in common for both sections.

Cheers,
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