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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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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 15 Dec 2016, 19:20 
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Better more than not enough. You can always cut it back.

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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 16 Dec 2016, 15:13 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
Ok the new Lacewood Amp is up and running. Here it is under test.
Attachment:
Under Test (s).jpg
I finally decided to use a 350Ω 5W dropping resistor in the the B+ after the first cap and before the first choke. Here are the resultant voltages in the amp.
Attachment:
Voltages (s).jpg
As you can see, the B+ came out just about 300V giving me a Vp on the tubes of just under my 275v target.

However, using the 392Ω cathode resistors made the bias voltage come out a little low. This resulted in a peak power just about 1dB below what I thought it should be. Peak clean output power is 3.125 watts rms. But it also resulted in lower distortion. Total harmonic distortion at 1w into 8Ω is 1.78% (1.66% 2nd & 0.66% 3rd). Here is the FFT.
Attachment:
Distortion at 1W (s).jpg
Ignore the 5th and 7th harmonics; those are a product of my signal generator.

So much for the Engineering data. Here's the real test. The amp sounds awesome! :thumbsup:

First, the sound stage is excellent. Very deep with excellent separation. Close your eyes and individual instrument and vocalist locations pop into place with no effort. This sound stage is infinitely better that the first version of the amp. Second, the sound is very clean and very balanced. It's the best of all the UL pentode amps I've built. It also seems a little quicker than the first version. Fast classical passages are like standing in front of the performers. Overall, I am extremely pleased with the results.

I'll get the final as-built schematics drawn up and posted this weekend along with some pictures of the new internals.


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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 16 Dec 2016, 17:06 
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The finale schematic will give me a chance to see how different mine is from the new V2. I'm also happy with mine but if the changes are easy enough I'll make them.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 17 Dec 2016, 13:55 
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The amp is complete and is situated in my electronics assembly area. Here are the final schematics. First the audio chain:
Attachment:
Rewire Schemaic Final (s).jpg
And the final power supply:
Attachment:
Rewire Schemaic PS Final (s).jpg

Here is what is looks like below the plate. Here's the overall view:
Attachment:
Final ReWiring (s).jpg
Here in the power supply section you can see the original 5H choke is gone, replaced with the two smaller Triad chokes. There is a large dropping resistor in the primary side of the power supply. On the audio side, things are very similar. The old volume control has ben replaced with a high quality PEC dual unit, the experimental wiring for signal sampling has been removed, and the twisted wire feeds to the power tubes have been replaced with single wires.

Here is a close up of the driver section:
Attachment:
Signal Section.jpg
This is much cleaner than it was previously.

Here is a close up showing how the power tubes are wired in:
Attachment:
Power Section.jpg

And finally, here is the primary side of the power supply showing the new dropping resistor:
Attachment:
Primary Power Supply.jpg

Some further impressions: As I said previously, the sound stage is awesome. Very detailed and wide. The amp is also dead quiet; not even the slightest hint of hum or hiss. Music seems to rise up out of the black abyss. Overall this is a huge success. There is still some final analysis work to do, but I am already enjoying this amp even more than before.

For anyone contemplating a Lacewood build, I highly recommend this version.


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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 17 Dec 2016, 17:32 
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Great!

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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 18 Dec 2016, 11:41 
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Nice. I like the beefed up PS.

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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 28 Dec 2016, 09:03 
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Joined: 05 Jun 2012, 13:10
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Location: Darboy, WI, USA
How's the amp treating you?

I've been wondering since you've suggested an Edcor power transformer previously and ended up using a resistor to lower your B+, do you suggest using the power supply schematic 'as-is' for a new build?

I'm getting ready to order some parts, so I'd probably go back and find the equivalent Edcor power xfmr, and similar for the first choke; I'd look for an equivalent Triad.

I already have some GXSE5-5.5k output xfmrs, and I'm guessing I will have a slightly smaller frequency range if I don't opt for the larger wattage iron?

Thanks Matt for your continuing contributions to this website/forum/community. I appreciate it.

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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 28 Dec 2016, 18:05 
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RossD, general the wattage of an OPT is quoted at full power. If you only playing the amp at 2W you will not saturate the amp and should get 40Hz and up. I used these OPTs in a EL34 amp which a friend heard and bought a few days after I made it. We both agreed that the bass was quite extended. I think you will be surprised.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 29 Dec 2016, 11:59 
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RossD wrote:
How's the amp treating you?
Very well. I really like the tone of the new amp. And I'm really enjoying the soundstage. This is now the amp to which I listen in my electronics work area. Nice sound and plenty of volume for the space.
RossD wrote:
I've been wondering since you've suggested an Edcor power transformer previously and ended up using a resistor to lower your B+, do you suggest using the power supply schematic 'as-is' for a new build?
I think I would use the same power supply schematic but replace the power transformer with the Edcor XPWR163 (http://www.edcorusa.com/xpwr163). I would also replace the Hammond 193J with an Edcor CXC100-7H-150mA. If you want it under the hood you could use Triad C-16X 6H 200mA choke as the main unit. I'd stick with the dropping resistor to fine tune the voltage. You probably could go to a 500VCT transformer like the XPWR221 but you'd have to use a GZ43 rectifier and then you'd be back to using a resistor to fine tune your voltage. I'd stick with the XPWR163 because it's cheaper and gives more flexibility.
RossD wrote:
I already have some GXSE5-5.5k output xfmrs, and I'm guessing I will have a slightly smaller frequency range if I don't opt for the larger wattage iron?
Edcor markets these as 40Hz to 18kHz the same as all their GXSE transformers (http://www.edcorusa.com/gxse5-55k) so I'd say you're good to go.

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 Post subject: Re: "Lacewood" Amp V2.0
PostPosted: 29 Dec 2016, 13:28 
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Location: Darboy, WI, USA
Thanks guys.

And I think you mean a Triad C-14X rather than C-16X.

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