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Old 12th July 2013, 10:11 PM   #1
riverty is offline riverty  United States
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Default 6V6SE - Suggestions?

I built this 6V6 SE amp. it works well and sounds pretty good although I think it could sound better. With that, I wanted to post the schematic and ask you all to take a look and possibly make suggestions on what *could* make it sound better and/or run better. Someone with a bit more tube amp experience than I.

Thank you all!
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File Type: pdf 6V6SE circuit 2.pdf (40.0 KB, 213 views)
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Old 12th July 2013, 10:22 PM   #2
tinitus is offline tinitus  Europe
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grid stoppers, and move att to input ?
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Old 12th July 2013, 11:43 PM   #3
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The schematic doesn't show a dc reference for the heaters. You should not have them floating.
Are the values of the coupling cap and volume pot right? Both look rather low to me.
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Old 12th July 2013, 11:50 PM   #4
tomchr is offline tomchr  United States
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Quote:
Originally Posted by tinitus View Post
grid stoppers, and move att to input ?
I second that!

In addition: You'll need a bleeder resistor on the main reservoir cap. Set it up such that it draws 1~2 mA and the cap will discharge in a few minutes.

The cathode caps need to be a lot bigger. I wouldn't go for less than 1000 uF here. I suppose, technically, 100 uF on the driver and 220 uF on the output tube would be enough, but why skimp?

I'd make the cap after the inductor in the supply quite a bit bigger as well.

~Tom
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Old 13th July 2013, 12:04 AM   #5
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3rd on moving the volume pot to the input and then reduce the 6V6's grid resistor to 470k, datasheet specifies no more than .5 meg for cathode bias and 100k for fixed.
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Old 13th July 2013, 07:04 AM   #6
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Put potentiometer 200 ohm between both ends 6.3 v for heaters. It meddle point to ground for adjusting hmm from heaters.
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Old 14th July 2013, 05:12 AM   #7
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by riverty View Post
I built this 6V6 SE amp. it works well and sounds pretty good although I think it could sound better. With that, I wanted to post the schematic and ask you all to take a look and possibly make suggestions on what *could* make it sound better and/or run better. Someone with a bit more tube amp experience than I.

Thank you all!
(1) You say it "sods good" but have to MEASURED it? It is unusual that a 6V6 sounds best in ultra linear mode. Try Pentode mode and see it it is better

(2) Same comment about lack of NFB. Have you measured performance (distortion) with and without NFB. It is uncommon for an amp like this to sound (and measure) better with no NFB

(3) I bet you $1 yor source already has a volume control. I don't know why people are saying to move you volume control. As placed it serves as a "gain control" And might be useful almost every guitar amp on Earth places the first volume/gain control after the first triode gain stage. Works fine, especially if you KNOW the source already has a volume control. If you do anything with it, simply replace with a fixed resister

(4) The tube rectifier adds nothing to the sound. On a class B amp it does, it adds a "compression" effect but on a class A amp, you my as well use diodes and gain more B+ voltage

(5) I like to both elevate the heater voltage and add a resistive "artificial center tap" and a bleeder resister. But this is ALL tried together. Start by using two resisters in series for the bleeder resister. use (say) a 470K and a 47K The junction gives abut 10% of B+ voltage, good for raising heaters. Connect that to the center tap.


For the most change in sound, try this mod: convert to Pentode mode. (don't use the UL tap) Add small amount of NFB. Adjust the gain pot for best sound and replace with a pair of fixed resisters. (a pot inside a NFB loop isnot going to work for anything but to adjust the NFB ratio.)

Doing the above should clean up the sound a yu likely have about 10% to 5% distortion right now. You can get it below 1% What you have right now look a LOT like a very "clean" sounding guitar amp
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Old 17th July 2013, 02:22 AM   #8
jjman is offline jjman  United States
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Originally Posted by ChrisA View Post
.............. It is unusual that a 6V6 sounds best in ultra linear mode. Try Pentode mode and see it it is better............................
Is this a consensus based truism or anecdotal or something else? I also have a UL 6v6 SE amp (no FB) and thought the consensus was that UL or triode “sounded best,” however 6v6 was not necessarily the tube being commented on. I don’t know what “sounds best” since I’m too new. Are 6v6 SE setups “different” in that the consensus “best sound” is achieved via different configuration than non-6v6 tubes?

Not intending to accuse. I really want to know since I do not know.
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Old 17th July 2013, 06:28 AM   #9
ChrisA is offline ChrisA  United States
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Originally Posted by jjman View Post
Is this a consensus based truism or anecdotal or something else? I also have a UL 6v6 SE amp (no FB) and thought the consensus was that UL or triode “sounded best,” however 6v6 was not necessarily the tube being commented on. I don’t know what “sounds best” since I’m too new. Are 6v6 SE setups “different” in that the consensus “best sound” is achieved via different configuration than non-6v6 tubes?

Not intending to accuse. I really want to know since I do not know.
I think it is a consensus opinion that the 6L6, 6V6, K88 and so on family of beam tetrodes are best used in Pentode or triode configuration.

You really have to get set up to measure amplifiers. Without the ability to measure performance or conduct double blind listening tests you are just arguing whose imaginary, invisible friend is taller. To measure all you need is an 8 ohm dummy load resistor a multi-meter and an audio interface for the computer with some free software.

Science, not opinion can tell you that going with triode mode will give the amp more power and this can compensate for the loss in gain the NFB brings. You will get higher bandwidth and lower distortion. But will you LIKE it more? Maybe not. Many people prefer the sound of an open loop amp running at about 10% THD. That just might be what you have.
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Old 17th July 2013, 03:43 PM   #10
TURING is offline TURING  China
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0.047uf too small.
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