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Old 15th February 2006, 01:42 PM   #11
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I have built Frank's 6SN7 circuit and it can indeed hold it's own. Use it with a very good psu and you are in for a surprise.

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Old 15th February 2006, 03:46 PM   #12
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Default Your friend's circuit

I just want to point ou that your friend's circuit is not a SRPP, rather a mu follower. In my opinion the B+ for this mu follower circuit could be higher, at the moment those triodes aren't running in a very linear region (that's more of a guess, but I always see 6SN7 circuits with more b+).

About Brians comment: There was a recent thread where someone showed two schematics from a preamp with the 6SN7, both from Frank, one with coupling capacitor, the other without (both where 1st stage: anode follower, second stage: cathode follower). Try to search for it.
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Old 15th February 2006, 07:04 PM   #13
chrisvw is offline chrisvw  South Africa
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Default Here you go...

Is this the image in question? Chris
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Old 22nd February 2010, 02:50 PM   #14
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Quote:
Originally Posted by refference View Post
Hi ,

This schematic is my favorite , it sounds great , has a low output impedance and is simple to build .

I built the version using 6SN7 , the version using 6CG7 , and the
best ( my favorite ) using 12AU7 / ECC82.

Try to build , don't using the 1K grid stopper resistors , all others
values are OK .

You will be very satisfied with the results

Regards

Carlos
Hi Carlos,

some questions:

1. Which tube did you prefer, the 6SN7, or the 6CG7?

2. Are you saying do not use a 1m resistor for a grid stopper? Then what value did you use?

3. Later on in this thread, there is a question about not using a coupling cap between stages? Did you end up removing that cap?

4. What is the output impedance of this preamp?

5. Since I am a blind person, can't see the pics, so does this schematic show the Power Supply too?

6. What transformer for the supply should I get? With the B+ and all of the correct voltages?

I think that is all for now. I was looking in to building a 12B4 preamp, but others have stated that there are better tubes out there like a 6n6p and so on. So back to the 6sn7/6cg7 tube.

Ray Bronk
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Old 25th February 2010, 09:32 PM   #15
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Quote:
Originally Posted by ray bronk View Post

1. Which tube did you prefer, the 6SN7, or the 6CG7?

2. Are you saying do not use a 1m resistor for a grid stopper? Then what value did you use?

3. Later on in this thread, there is a question about not using a coupling cap between stages? Did you end up removing that cap?

4. What is the output impedance of this preamp?

5. Since I am a blind person, can't see the pics, so does this schematic show the Power Supply too?

6. What transformer for the supply should I get? With the B+ and all of the correct voltages?

Ray Bronk
Hi Ray ,

First of all , I'm talking about this schematic . A " U follower " .
A pre amp with 12AU7 , as I had said , my favorite , in the second place
I'd prefer the 6CG7 .
Suposing that you will follow me and use the 12AU7 , the answers are :U follower schematic.jpg

1 ) Neither one , I prefer the 12AU7

2 ) You can use the grid stopper resistor of 1000 ohms ( 1 K )

3 ) In this stage , U follower , the coupling capacitor is essential , and must
be polypropylene or oil , 0.022 uF x 400 V , the value of 0.22 uF x 250 V , is
not a good choice ( IMO ) because the time constant too high .

4 ) The output impedance is about 800 ohms ( with 12AU7 )

5 and 6 ) The power supply I use a transformer with an output of 270 V AC x 50 mA , bridge rectified , 150 uf as the first cap , a 10000 ohms ( 10 K ) x 3 W resistor , then a 180 uF x 400 V , then , 2 ( two ) 10000 0hms ( 10 K ) x 3 W resistors , each one feeding a 180 uf x 400 V capacitor , each one for each channel , this way the final voltage will be aprox. 265 - 270 Volts on the plates , that is the ideal value for the 12AU7 .

The resistors values on the table are correct , the only change I would do is
the cathode by-pass capacitor , 100 uF x 25 V instead 33 uF x 25 V .

Good Luck .
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Old 26th February 2010, 12:27 AM   #16
Cassiel is offline Cassiel  Libya
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I have tried both, I like best the mu follower but the CF sounds good too.
I used a tube regulated power supply.
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Old 26th February 2010, 04:12 AM   #17
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I built Frank's preamp using the 12BH7A schematic and am very pleased...although I wonder what the difference would have been had I chosen to go the 6SN7 route.... has anyone tried both??
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File Type: jpg IMG_1170.jpg (304.4 KB, 1079 views)

Last edited by huskydawg9; 26th February 2010 at 04:29 AM. Reason: add pic
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Old 3rd April 2010, 03:45 PM   #18
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Quote:
Originally Posted by huskydawg9 View Post
I built Frank's preamp using the 12BH7A schematic and am very pleased...although I wonder what the difference would have been had I chosen to go the 6SN7 route.... has anyone tried both??
Hi, Just curious why did you use a 12BH7 as opposed to the 12AU7 or the 6SN7 or 6CG7 tube? I am not doubting your choice for the tube used. Have been looking around for a good tube preamp to build. Was interested in the 12B4, but people out there saying the 6H30 or even the old venerable 6SN7 or 6N1p is better. Anyway, just curious at this point.

Ray Bronk
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Old 3rd April 2010, 03:56 PM   #19
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Quote:
Originally Posted by refference View Post
Hi ,

This schematic is my favorite , it sounds great , has a low output impedance and is simple to build .

I built the version using 6SN7 , the version using 6CG7 , and the
best ( my favorite ) using 12AU7 / ECC82.

Try to build , don't using the 1K grid stopper resistors , all others
values are OK .

You will be very satisfied with the results

Regards

Carlos
Hi Carlos,

Thanks for your reply. So why is the 12AU7 your favorite? I have none. All of the reading around the web suggests the 6SN7 is more linear than the 12AU7, and might be more open too. Also, converting the 12AU7 to a 6CG7 is not difficult. Disconnect Pin 9 and make sure that whatever is connected on pin 5 is moved to pin 4, and move connection from pin 9 to pin 5. Also, the heter supply instead of 12 has to be 6 with the current draw rating twice as much for the 6.3 filament. There, essentially you shouldn't according to what I've read, have to change anything in the circuit for the 6CG7 to work. Anyhow, just curious why you like the 12AU7 tube. Again, no preference for me.

Ray
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Old 3rd April 2010, 04:43 PM   #20
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Quote:
Originally Posted by ray bronk View Post
Hi, Just curious why did you use a 12BH7 as opposed to the 12AU7 or the 6SN7 or 6CG7 tube? I am not doubting your choice for the tube used. Have been looking around for a good tube preamp to build. Was interested in the 12B4, but people out there saying the 6H30 or even the old venerable 6SN7 or 6N1p is better. Anyway, just curious at this point.

Ray Bronk
The original thread used the 12BH7, so I went with that. Although because of your comment, I just swapped out the 12BH7's with a pair of 12AU7's and I have to admit it opened things up quite a bit.
I rolled a ton of different tubes in my "Bijou" headphone amp...and the 6H30 by far is my favorite, followed by the 6N1P
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