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SE 6L6 power amp, 12AT7 driver (design by Suncalc)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5731
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Author:  mwhouston [ 25 Feb 2017, 07:28 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

http://www.thetubestore.com/Resources/Product-Reviews/6L6-Tube-Reviews-Chart

A chart of 6L6 characteristics .

Author:  mwhouston [ 01 Mar 2017, 21:36 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

How the project was always intended except I'm using a NOS Phillips miniwatt 12AU7 as driver. Bit smelly as the high temp paint I sprayed the tubes in burns in. Sounds excellent.

Author:  mwhouston [ 01 Mar 2017, 21:37 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Is this sharper
Attachment:
image.jpeg

Author:  mwhouston [ 02 Mar 2017, 06:39 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Though pleasant sounding I may try this amp with one of he Psvane 12AT7 "T" series MKII. Nice but not a patch on "Silver Supreme".

Author:  mwhouston [ 03 Mar 2017, 20:44 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

It appears the 12AT7 may be the big contributor to the overall sound of this amp in the configuration just above. Wouldn't have thought so but happy to be wrong. Waiting for all tubes to fully burn in. At least the smell of baking high temp paint has gone.

If you have an 4SU preamp and a reasonable AT about give it a try. The tube seem so have a little sparkle to it. My usual U7 is more mellow, the T7 brighter.

Author:  mwhouston [ 11 Mar 2017, 21:22 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

I put the Silver Suoreme to the CRO today.

Peak power = 1.9W RMS into 8.2omhs @ 1KhZ
Lower 3db point = 60hZ @ 1.9W
Upper 3db point = 47Khz @ 1.9W
Gain = 23db
Input Voltage for full power = 770mV @ 1KhZ into 8.2ohms.

100hZ SQR wave = awful
1KhZ SQR wave = not good
10KhZ SQR wave = very good with a little controlled over-shoot
15KhZ SQR wave = very good with a little controlled over-shoot.

As you can see the low frequency response test is quite poor. The strange part is the bass sounds so much better than it tests. I always felt this amp had excellent mid and upper frequency response and I guess the testing has proved what I hear. No real surprises here. Still a great amp to listen to.

Author:  Suncalc [ 12 Mar 2017, 11:35 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

mwhouston wrote:
Lower 3db point = 60hZ @ 1.9W
mwhouston wrote:
As you can see the low frequency response test is quite poor. The strange part is the bass sounds so much better than it tests.
This is simply a consequence of the relatively high effective plate resistance of the 6L6 in UL configuration in combination with low output transformer input inductance. During the design process I estimated the 6L6 plate resistance, at the operating point, at ≈3.33kΩ. The Edcor XSE10-8-5K I had on hand seemed to have a primary inductance of about 5H with a 150Ω series resistance. Using these values I just generated the plot below.
Attachment:
6L6 UL Rolloff.png
As you can see, the -3dB point comes in at about 63Hz on the plot. Your CRO reading of 60Hz seems very reasonable given what we know about the design. And given your impressions of the amplifier, clearly having a 60Hz low end rolloff is not really a problem for a lot of listening.

I didn't mention this earlier because I hadn't done any detailed calculations for the power stage rolloff. And I didn't think it would really matter for a small amplifier like this one. The average person's normal hearing has a rolloff at 60Hz of between -40dB and -48dB from midband sensitivity. And at 40Hz it's between -55dB and -60dB! Unless the power levels are really elevated, the low end is generally masked by ambient environmental noise unless used in a VERY quiet listening environment.

If the amp sounds good to your ears, I wouldn't even think about the CRO data. Sometimes I intentionally don't measure frequency response just so that the raw data doesn't distract me from how the amp really sounds.

Author:  mwhouston [ 12 Mar 2017, 17:21 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

It's hardening g to see the maths and the modelling agree with measurements. And strange to realise what we can quantify not always agrees with what we experience. Ground shaking bass or not the amp is a delight to listen to and novelty to look at. Today I'm to measure one of my T3 Tripath class D monoblocks. I'm expecting much better bass measurements but that doesn't always translate to more musical enjoyment.

Author:  mwhouston [ 14 Mar 2017, 04:12 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Matt, if I upgraded to the 15W Edcor OPTs (15-8-5K) would I gain more bass? Or dose the maths say no?

Author:  Geek [ 14 Mar 2017, 04:29 ]
Post subject:  Re: SE 6L6 power amp, 12AT7 driver (design by Suncalc)

Suncalc wrote:
If the amp sounds good to your ears, I wouldn't even think about the CRO data. Sometimes I intentionally don't measure frequency response just so that the raw data doesn't distract me from how the amp really sounds.


That's a key reason a lot of ultra-high-end boutique manufacturers don't even spec their amps... your ears like it or your ears don't ;)
(I literally tell my customers, "Want great specs? Go to the Best Buy techs. Want great sound? Stick around!" :D )

But if bass response is an issue, I'll toss out the CFB trick of running the 6L6 cathode throug the speaker side of the OPT - it desaturates the transformer somewhat and lowers the tube anode-Z, getting you more bottom with any existing transformer... some more than others :beerchug:

Cheers!

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