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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: 6V6 Marblewood Amp
PostPosted: 02 Nov 2018, 20:23 
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Joined: 04 Jun 2008, 20:59
Posts: 4052
Location: Arizona, USA
Hi, I have used the JJ 6L6GCs and they are quite nice. I also tried some Sovtek 6L6WXT+ A slightly beefier version of the tube. (guitar folks like the way the overdrive BTW) They also are good in SE U/L use. If you have enough heater power you might give a try to KT120s. No other changes. I recently stuffed some in my KT77/EL34 Oddblocks and was really impressed with the sound. I have heard that "big bottle" tubes sound better than their skinnier mates. I am becoming a believer. All my personal mono blocks are running with KT120s. B+ of 450 and cathode current per tube is 62 ma. They just loaf along. I would expect some vintage large bottle tubes to be nice as well. Older 6V6G, 6L6G, KT66 and so on.

I agree with Mark your stuff looks great.....makes mine look like garage builds.

Good listening
Bruce

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 09 Nov 2018, 23:02 
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Joined: 06 Jun 2008, 18:23
Posts: 5151
Location: Australia
Matt having built a 6V6 and a 6L6 power amp you may like to highlight your preference. To you, which amp sounds the best and why.

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 09 Nov 2018, 23:07 
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Joined: 06 Jun 2008, 18:23
Posts: 5151
Location: Australia
gofar99 wrote:
Hi, I have used the JJ 6L6GCs and they are quite nice. I also tried some Sovtek 6L6WXT+ A slightly beefier version of the tube. (guitar folks like the way the overdrive BTW) They also are good in SE U/L use. If you have enough heater power you might give a try to KT120s. No other changes. I recently stuffed some in my KT77/EL34 Oddblocks and was really impressed with the sound. I have heard that "big bottle" tubes sound better than their skinnier mates. I am becoming a believer. All my personal mono blocks are running with KT120s. B+ of 450 and cathode current per tube is 62 ma. They just loaf along. I would expect some vintage large bottle tubes to be nice as well. Older 6V6G, 6L6G, KT66 and so on.

I agree with Mark your stuff looks great.....makes mine look like garage builds.

Good listening
Bruce

I too have the JJ 6L6GC in one wine box amp. They are a big impressive tube. Really like them in my wine box amp but when searching for more bass the Class D T3s provide it. I've been off tube power amps in my main system for some time now and are missing the sound. Bass or not I may have to swap in the wine box or two just for fun. I do like the mids of tubes.

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 28 Jan 2019, 19:52 
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Joined: 22 Aug 2017, 21:57
Posts: 11
Location: Layton, Utah, USA
I built Matt's excellent marblewood amp a few months ago, and I like it a lot. I made PCBs, one for the 12AU7 and one for the 6V6s. The power supply is point to point wired. The chassis and bottom plate are plasma cut steel, painted with black Rustoleum. The wood is marblewood like the original, very beautiful wood, but kind of expensive. I completed the testing today using ARTA Steps software and my Steinburg UR22 MKII USB audio interface, so I thought I'd post the results here. There are 3 separate graphs of the frequency response and THD at low drive (abt 250mv RMS), moderate drive (abt 500mv RMS) and high drive (abt 800mv RMS). The 3dB bandwidth is from about 42Hz to 20KHz+, gain of about 45dB. Distortion at 1KHz ranges from less than 1% at low drive to about 3% at high drive. Distortion is primarily 2nd harmonic as expected. I have only tried the 12AU7 and 6V6s (all JJ Elect.) and haven't had a chance to do any tube rolling yet.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 28 Jan 2019, 19:55 
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Joined: 22 Aug 2017, 21:57
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Location: Layton, Utah, USA
Here's the distortion graphs.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 28 Jan 2019, 20:31 
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Joined: 06 Jun 2008, 18:23
Posts: 5151
Location: Australia
Gorgeous build.

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 30 Jan 2019, 17:02 
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Joined: 22 Aug 2017, 21:57
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Location: Layton, Utah, USA
Sorry but my ARTA system was not calibrated when I made the previous measurements so the gain was way off. Here are the corrected graphs.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 30 Jan 2019, 19:24 
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Joined: 23 Feb 2017, 02:02
Posts: 559
Is there any load on those results, you've said a gain of 45db = 10^(45/20) = gain of 178X
Low drive of 0.25V*178=output v of 44.5V rms into 8R.

Thats a peak power of (44.5*44.5)/8= 247.5W and 123.5W RMS (P=(V*V)/R)


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 24 Nov 2019, 01:08 
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Joined: 23 Nov 2019, 22:04
Posts: 1
I've also built Matt's Marblewood amp recently but have it in a slightly different case so I call it my GlassAmp. It's my first amplifier build so thanks to Matt for making it so easy and clear and everyone else on this site for all the help you have been without knowing it. Most of the questions and lack of understanding I had were able to be rectified by various articles and posts I found on this site.

I went for full point-to-point wiring as it matched the naked and nothing hidden aesthetic I was looking for and I could copy the excellent photos provided. The only changes I have made is to add an earth chassis circuit (for obvious reasons!) an extra input and input switch and remove the dropping resistor as I found that was the only way I could get 300v on the B+. I suspect this might be because I'm using the suggested Edcor transformer wired for 240v but here in NZ the mains voltage is actually 230v.

The case I designed in Inkscape, an open source vector drawing program and got it laser cut from clear glass-edge acrylic with mirrored acrylic on the bottom. I used 6mm for the top surface to get the heavy solid glass look. I especially like the 21st century digital fabrication techniques meets 1950s valve technology! I was aware that the acrylic would not provide any shielding so I was resigned to needing to chase down some sort of hum or interference but to my surprise it was dead quiet when I first switched it on. So quiet that I initially thought it wasn't working and I'd need to go through everything step by step, but I fed it an input and it was away laughing!

Most importantly it sounds amazing especially for jazz quartets and soloists/vocalists really feel like they are there in the room with you. The imaging is a significant step up from my previous hobbled together system (NAD pre from an integrated amp and Arcam Alpha 8 power) although perhaps not quite so versatile. My only criticism is that the bass seems a little weak but I suspect this has more to do with my little 20 yr old bookshelf bass reflex speakers. I have a high sensitivity full range driver in a horn enclosure on my do-do list. But probably after a tube phono stage as I can still hear the clinical nature of the Project phono-box I'm currently using.

I don't have any test equipment other than a pretty basic multi-meter so I don't have any hard data on distortion etc but I can give you some voltages if anyone is interested!

I can also upload the case plans if anyone wants them.

-Brendhan


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 26 Nov 2019, 13:14 
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Joined: 06 Apr 2009, 10:08
Posts: 1596
Location: US Pacific Northwest
Brendhan, well done! That is one very cool case.

I had never considered an acrylic case before and yours is top notch. I really like it.

Matt

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