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Old 14th March 2013, 05:58 PM   #1
Gost22 is offline Gost22  Bolivia
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Default New vacuum-tube preamp-project!

Hi guys!
I make some preparations for the development of tube preamps with 6922 or 6n23p, ECC88, 6JD8 and etc,.
First, go to the schematics (see Figure1 and Figure2).
Which schematic is better in your opinion, so let's move on ...
Thank you for your cooperation, going on, ..
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Old 14th March 2013, 06:17 PM   #2
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The second drawing has a mistake. The diode is useless and in fact rectifies signal causing distortion.

Also a resistor from arm of pote to ground is useless too.

Finally, I would wire them in DC and plate of first triode bootstrapped from cathode to augment gain and lower distortion. http://www.freewebs.com/valvewizard1/dccf.htm, last schematic.
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Old 14th March 2013, 06:23 PM   #3
Gost22 is offline Gost22  Bolivia
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Quote:
Originally Posted by Osvaldo de Banfield View Post
The second drawing has a mistake. The diode is useless and in fact rectifies signal causing distortion.

Also a resistor from arm of pote to ground is useless too.

Finally, I would wire them in DC and plate of first triode bootstrapped from cathode to augment gain and lower distortion. The Valve Wizard, last schematic.
Mr. Osvaldo already-known theoretical things first.
Diode is not too much!?
Question: why does she serve?
Please be specific with the answer of the question, ....
thank you!
P.S.
Here are the boxes that I prepare for this High-End tube/valve preamplifier!
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Last edited by Gost22; 14th March 2013 at 06:32 PM.
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Old 14th March 2013, 06:37 PM   #4
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Diode SS and diode grid cathode are in parallel and have no DC return. A small AC voltage positive going will be rectified charging coupling cap negative to the side of grid. So in few cycles second tube (Cathode follower) will go cutoff as negative voltage always increases and can't decrease., and first, severe audio distortion will be heard, and then completely no sound until the cap discharges in its own self leakage.(You must turn off power to let the cap discharge). The circuit is completely useless.

Salu2 de Argentina.
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Old 14th March 2013, 06:42 PM   #5
Gost22 is offline Gost22  Bolivia
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Mr Osvaldo,
Somehow, English is not my better half, so please show the changes to the schematic and to talk a little more specifically, ...
thank you
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Old 14th March 2013, 06:50 PM   #6
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I'll send you a PM in Spanish. Wait for me till tomorrow.
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Old 14th March 2013, 06:52 PM   #7
Gost22 is offline Gost22  Bolivia
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I'll send you a PM in Spanish. Wait for me till tomorrow.
ha,..ha, OK!?
P.S.
Congratulations on all Catholics choice POPE.

Last edited by Gost22; 14th March 2013 at 07:09 PM.
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Old 15th March 2013, 08:33 AM   #8
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Quote:
Originally Posted by Osvaldo de Banfield View Post
Also a resistor from arm of pote to ground is useless too.
Not completely useless: it keeps the grid grounded if the pot wiper loses contact, thus protecting the tube. Mandatory with stepped attenuators.
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Old 15th March 2013, 08:56 AM   #9
SY is offline SY  United States
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Hasn't this thread already appeared twice before with the exact same questions and the exact same schematics?

If you want to build something, put down the pencil and paper and go do it.
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Old 15th March 2013, 10:45 AM   #10
DF96 is offline DF96  England
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Didn't someone once say something about someone who keeps repeating the same action but expecting a different outcome?
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