New Years Eve 6LU8 amp

the thermionic watercooler

New Years Eve 6LU8 amp

Postby TomMcNally » Fri Dec 31, 2010 3:09 pm

I just built this today. It uses 6LU8 Compactrons, and a GZ-34 rectifier.
The 6LU8 has been likened to a 12AT7 and a 6AV5 or EL-34 in one bottle.
I used an Edcor XPWR007 power transformer, GXSE15-8-5K OPTs and
a pair of Radio Daze RDC-100 chokes in series, with lotsa MFD's.
The thing kicks ass, and sounds really good.

More pix at http://tmamps.com

ImageImageImageImage

Here's a link to the original design ...http://www.audiokarma.org/forums/showthread.php?t=163886
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Postby TerrySmith » Fri Dec 31, 2010 6:12 pm

Wow, that's pretty sweet! I like it when you use odd-ball tubes and it turns out nice. Is it triode connected or UL?
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Postby TomMcNally » Fri Dec 31, 2010 6:37 pm

It seems like an ideal tube for a "spud" amp.

It's set up for UL operation.
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Postby Geek » Fri Dec 31, 2010 10:20 pm

I just got a box of these. I'll have to give it a whirl :-)

Cheers!
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Postby Sal Brisindi » Sat Jan 01, 2011 1:15 pm

Looks nice Tom,
I like the wide stance chassis you used. So how long did this one take to build, 2 hours?... :-)

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Postby EWBrown » Sat Jan 01, 2011 10:15 pm

Nice one! (love)

Those duodecar compactron sockets can be a real bear for point-to-point wiring, you did a very nice job.

I ckecked over at the Audio Karma site, and I spotted a major error in this particular 6LU8A amplifier's power supply wiring:

(I checked a DIY-ST-35, with a AN2T300, which I built about 3 years ago, in order to verify this ,before posting it)


The rectifier tube is a 6BY5GA, with the plates on pins 4 and 5, and the cathodes on pins 1 and 8, and the heater on 2 and 7.

See if you can spot the error, before reading my explanationposted below the photo.


Image


----------------------------------------------

With the Antek PT's two yellow leads connected to the 6BY5GA's rectifier tube anodes, and the two white leads connected together as the center-tap.

What this does is create a paralleled half-wave rectifier, rather than a full-wave center tap situation, which would be the correct one. FWIW, this isn't the first time that I've seen this particular wiring error, with an Antek PT.

I posted a reply to this effect over there, for the builder.

/ed B
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Postby kheper » Sun Jan 02, 2011 6:42 pm

EWBrown wrote:With the Antek PT's two yellow leads connected to the 6BY5GA's rectifier tube anodes, and the two white leads connected together as the center-tap.

What this does is create a paralleled half-wave rectifier, rather than a full-wave center tap situation, which would be the correct one. FWIW, this isn't the first time that I've seen this particular wiring error, with an Antek PT.

/ed B


From what I can tell from Antek's specs, for a full-wave center tap, the "inner" yellow from one winding and the "inner" white from the other winding need to be connected, then grounded.

http://www.antekinc.com/pdf/AN-2T300.pdf

What am I missing?
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Postby EWBrown » Sun Jan 02, 2011 9:22 pm

From what I can tell from Antek's specs, for a full-wave center tap, the "inner" yellow from one winding and the "inner" white from the other winding need to be connected, then grounded.


That is correct.

In the "wooden" amp, the two yellow leads are connected to the rectifier anodes, and the two white leads are used as the ground / zero volts / centertap. With this conenction, the rectifiers will behave as two paralleled half-wave rectifiers, and not as a center tapped full wave.

The usual result of half-wave rectification would be reduced B+ voltage and a serious 60 Hz ripple / hum problem.

/ed B
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Postby kheper » Mon Jan 03, 2011 8:42 am

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Postby EWBrown » Mon Jan 03, 2011 8:07 pm

6LR8 is an alternative, equivalent tube, it has the same triode and pentode same "innards", but packaged in a Novar (9 pin compactron)
T-12 envelope.

http://frank.pocnet.net/sheets/135/6/6LR8.pdf

Might be a good alternative if the crowded and close contact spacing of a duodecar socket is a bit too intimidating =:o

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