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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: 31 Mar 2018, 17:10 
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harrydutt wrote:
I already have a pair of Edcor GXSE15-5K opt's - https://www.edcorusa.com/gxse15-8-5k , are these okay for this amp ?
These outputs will work great! They will also give you a better low end frequency response.
harrydutt wrote:
Would this Edcor power transformer be suitable - https://www.edcorusa.com/xpwr072 (120V, 60Hz. line to 550V (275-0-275) at 250mA center tapped and 6.3V at 7A.) ?
Yes If you already have it. But the excess current is really not required for this build. Personally, unless you already have it, I'd go with the XPWR106 and save yourself the $10!

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 01 Apr 2018, 09:23 
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Suncalc wrote:
harrydutt wrote:
Would this Edcor power transformer be suitable - https://www.edcorusa.com/xpwr072 (120V, 60Hz. line to 550V (275-0-275) at 250mA center tapped and 6.3V at 7A.) ?
Yes If you already have it. But the excess current is really not required for this build. Personally, unless you already have it, I'd go with the XPWR106 and save yourself the $10!


Okay, thanks Matt, I'll go with the XPWR106 when I'm ready to go ahead with my build.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 01 Apr 2018, 11:28 
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Happy Easter!

I just wanted to post a quick note about the power transformer for this project. Talking with Harry got me looking at the XPWR106 again. For those looking at the forum thread or project page with sharp eyes, you will likely notice this:
Attachment:
XPWR106-120 Wiring.jpg

Specifically, there are only two wires for the primary. If you order the XPWR106 today, you likely get a transformer with a primary that looks like this:
Attachment:
0003454_xpwr106.png

This is because when I bought the transformer I used in this project, Edcor was offering this transformer in several specific primary configurations. (It's been sitting in my parts stash for a while.) Now the transformer is offering only two configurations a 120/240v universal primary and a 100v 50/60Hz primary specifically for Japan.

So don't be surprised when you order an XPWR106 and you get a transformer with four primary wires instead of two. Just make sure you wire the primary according to your local power standard.


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PostPosted: 04 Apr 2018, 14:54 
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The 6W6 tube has a relatively low rated screen grid voltage. The RCA datasheet has a maximum rated screen
voltage of 150V. Does this present any problem using this tube in the amplifier ?


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 04 Apr 2018, 18:19 
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harrydutt wrote:
The 6W6 tube has a relatively low rated screen grid voltage. The RCA datasheet has a maximum rated screen voltage of 150V. Does this present any problem using this tube in the amplifier ?
Nope! I'm listening to the Marblewood right now with 6W6s in it.

This is a consequence of the way the tube behaves in the UL mode. You'll notice that the 150v max screen voltage is for pentode operation, and it's omitted for the triode ratings. But in triode mode, the max screen voltage is 300v, by definition. So you might contend that it's somewhere in between. But that's not quite correct either because any "limit" is dependent on the AC condition, not the DC condition. The functioning of UL mode places a unique coupling between the plate and screen currents (via the output transformer secondary) which actually seriously restricts the screen dissipation. In fact, you'll note that at the zero signal condition, in UL mode the screen voltage is actually GREATER than the plate voltage (if only by a handful of volts). Again, by definition.

This is another benefit of UL mode; it's much easier on tubes than pentode mode.

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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 26 Apr 2018, 11:57 
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Joined: 13 May 2016, 02:02
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Location: Javea, Spain
Hi Matt,
Pretty amp!!! I'd like to build the Marblewood but I'm thinking of including a tone stack after reading the Baxandall Tone Stack thread from 2015.
Did you ever build the preamp with 2 treble, 2 bass and 2 volume controls?


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 06 May 2018, 12:20 
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Location: Javea, Spain
Okay, just read more from both threads (Baxandall and Marblewood). Beginning to understand that some things can't be cobbled together. Seeing your build of a mono tone stack I assumed it could be inserted into an existing circuit eg. the Marblewood. I've got to learn to read more before jumping to conclusions.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 29 Aug 2018, 11:46 
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First of all... I appreciate the level of detail that you go into. Makes your projects attainable to beginners (like myself). I've decided on this as my first exposure to tube amps and have been combing through your documentation trying to gain an understanding of everything.

Got a couple questions to make sure I don't end up buying the wrong parts... I'm assuming that unless specified otherwise I'd need to get 1/2 watt resistors. Is that correct?

I'm also unsure what voltage of caps to get for the preamp. It also looks like a couple of the caps are film caps. If so which ones are they?

Forgive my ignorance. I have the bad habit of bitting off more than I can chew.

Thanks! Keep up the awesome projects.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 02 Nov 2018, 11:56 
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Back to the JJ 6L6s, with a 12AU7A driver, in the Marblewood today.
Attachment:
6L6 Marblewood.jpg
These JJ 6L6GCs sound excellent in this amp! :sing:

The versatility of this amp is really amazing.


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 Post subject: Re: 6V6 Marblewood Amp
PostPosted: 02 Nov 2018, 17:35 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
I posted a comment about 6J6 tubes then realised your tubes are 6L6. Don't know the tube and never tried it.

Sometime later in the morning; Silly me I'm thinking I have never used a 6L6 tube in an amp but really I have two wine box amps with the tube. One pair JJs and the other pair 1945 metal JAN tubes. I never liked them in a PP UL amp but in the wine box builds thought they are excellent. I'm driving them with a 12AT7 Psvane top of the range. Yep, really like the sound.

These days the amp has been moved to system two which I only use for FM back grounds music but still nice to have them in service.

Matt, your bases are always excellent looking.

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Last edited by mwhouston on 02 Nov 2018, 21:13, edited 2 times in total.

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