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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 20 Feb 2019, 06:46

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PostPosted: 08 Feb 2019, 14:08 
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Joined: 09 Oct 2012, 19:43
Posts: 329
Location: Vancouver Canada
Just what I was looking for. Thank you Bruce.


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PostPosted: 11 Feb 2019, 00:05 
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Joined: 01 Oct 2017, 23:26
Posts: 8
I have built this amp according to the schematic and have quite enjoyed the results. I did some experimenting to flavor the sound more to my taste. Since it is such a simple circuit, very small changes can be readily heard.

The biggest change in sound quality came when I ran the ground of the CCS to a -6 V DC supply. The sound was much more clear and detailed. I am thinking that the LM317 is running in a non-linear area with the cathodes at the typical 2.5 V or so. Connecting the LM317 to a negative voltage allows it to work in a more linear region since the voltage difference is now around 8.5V instead of 2.5V. Or course this adds complexity to the amp, but I think the results are worth it. I ended up adding a separate 6V transformer and rectifier to build a separate CRCRC filtered supply for the CCS.


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PostPosted: 11 Feb 2019, 00:21 
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Joined: 01 Oct 2017, 23:26
Posts: 8
I almost forgot, since I didn't need the cathode to have as much voltage to make the CCS work, I also lowered the B+ to 125V and the current to 20mA per channel. The tube is still operating in a linear region, it is just is not as close to maximum dissipation now so it should last longer.


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PostPosted: 11 Feb 2019, 08:45 
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Joined: 04 Jun 2008, 20:59
Posts: 3916
Location: Arizona, USA
Hi, that is fine. I have not had any tube failures in this circuit yet. But it is running close to max dissipation. The alternative to a negative supply is to apply an equal positive voltage to both grids like in the Poddwatt DMBs. The LM317 ought to be a TO-220 type though as its dissipation is more but no heat sink is needed. This will keep the 317 from the non-linear region below +4VDC. It will allow for more output. But the level in mine is really much greater than needed. Up to 50mw of so is super clean. Down below 0.4% distortion. You can get a lot more power but the low gain of the amp means it will need more signal than many sources can provide. This is after all a super simple, low cost design. I have a big guy in the works at present that can deliver over 1 watt and will do desktop speakers as well as phones. The initial one ought to be ready this week.

Good listening
Bruce

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