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The "$250" Amp? - 6LU8 Compactron SE, UL

AC noise on my output terminals has gone down a tremendous amount.

I've reduced from 400uf of capacitance to 175uf total and now have 3.2mv of AC vs 5mv before with the extra C.

I also corrected this with my little 6v6 console I rebuilt for a friend - again reduced capacitance from about 500uf to 300uf and much quieter.

Seems the top end has cleared up also. Chris made the same mistake with his monoblocks (my fault, lol) and he claimed the difference was dramatic.

I do take Chris with a grain of salt however given that his CD player costs nearly what I paid for my car. :)
 
Ahh, good I was just gunna ask about the voltage.. :)
(yah that Chris character):scratch2:

I'd be curious if Goya got some extra voltage there as well.
 
All must bow down and kiss my CD players butt! Dan Wright is the man!

Seriously though, the PS correction sounded like a piece of carpet had been removed from the front of my speakers. Thats the last time I ask PHS for wiring advice... My advice is do your own research and don't put candy canes on your lawn. The overall sound was more defined. The bass sounds more controlled and all instruments and vocals sound closer to being real.

And Rage, don't be h8n ;)
 
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better watch it chris or the choker amps will get ya....:nono:
 

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Just finished reading all 62 pages of this thread LOL. Very interesting stuff, learning lots. Great looking stuff everyone! Thinking about starting up my first amp build soon.

Somewhere in the thread I read about plans for putting in a UL/Triode switch. Did anybody ever try that? Results?
 
I never did a switch, but I tried Pentode, Triode, and UL.

UL won out by a pretty far margin, the combo of shade style
feedback and UL just seems to work extremely well together.
 
Guys,

Thanks for this thread. I been up all night baby sitting a stupid server rebuild and without something like this. Well never mind.

So a question. I don't have a ton of heavy duty tools and aesthetics matter to me. Any ideas of a cab build for this that can be done with simple power tools. I am not gonna bend metal or do any heavy duty wood work. Nor will I do a cake pan. Not to say those are bad designs rather I think they are awesome.

Just looking around here and wondering maybe take a old stereo (Transistor POC) and mod it up a bit. Or maybe a server cab.

Just wondering what you guys do to build cabs without having a machine shop. I am guessing an all acrylic build would be bad with all the heat and stuff right ??

I could use these techniques.

http://www.audiokarma.org/forums/showthread.php?t=149130

And if I am wandering the thread slap me silly as I prob need to wake up to check the scrolling text from this forever data copy. :)

Thanks!!

Frannie
 
Obviously, I'm not the guy to ask about ending up with a nice looking finished amp. :-)

But I would avoid the acrylic idea because of the reason you name. I have some scorch marks on the wood near my tube sockets.

How about some flat sheet metal sitting on a nice wood frame? You could drill your socket holes with a step bit.
 
Hiya,

Thanks for the answer and I might move my query as to not pollute this thread with my idiosyncrasies. :)

Main issue is that I am living in a Baltimore Row house. I want to avoid anything that requires machining as right now until I work out something to get the basement setup. I am pretty much doing this work on the same desk as my work PC (Within a few feet) so I am worried about shavings and such getting into things. Not to mention the real evil (Love ?? ) that lurks which is my cats.

I maybe need to find a shop to do it right. Wood I may be able to wing on the rear deck using one of those workmates.

Acrylic might be nice to enclose it though. Keep le purr from getting into high voltages.

Thanks!!

Frannie
 
buglegirl said:
Guys,

Thanks for this thread. I been up all night baby sitting a stupid server rebuild and without something like this. Well never mind.

So a question. I don't have a ton of heavy duty tools and aesthetics matter to me. Any ideas of a cab build for this that can be done with simple power tools. I am not gonna bend metal or do any heavy duty wood work. Nor will I do a cake pan. Not to say those are bad designs rather I think they are awesome.

Just looking around here and wondering maybe take a old stereo (Transistor POC) and mod it up a bit. Or maybe a server cab.

Just wondering what you guys do to build cabs without having a machine shop. I am guessing an all acrylic build would be bad with all the heat and stuff right ??

I could use these techniques.

http://www.audiokarma.org/forums/showthread.php?t=149130

And if I am wandering the thread slap me silly as I prob need to wake up to check the scrolling text from this forever data copy. :)

Thanks!!

Frannie
Click to expand...

Frannie, if I were you, I'd go to your closest Harbor Freight and invest in a sheet metal brake (an 18" bench model should be fine for amp building) and some step bits and then pick up a good used bench model drill press off of CL(or a new one from Home Depot). Once you get adept with both of these, you'll be able to do an amazing amount of custom amp chassis building for relatively little cost (raw sheet steel is pretty cheap) if not a certain amount of sweat equity. Top it off with some self-etching primer and some hammertone paint and you're good to go.

-D
 
Hiya,

Excellent ideas except.

Problem is that I have maybe 3 feet by 3 feet to work with. Consider this also. This is a amp for the people so to speak.

The enclosure and how to achieve that maybe should been part of it. Although the creative aspect I certainly understand.

I have a set of ideas I am formulating here. Sorry I am so vague as I am getting a handle on this myself.

Frannie
 
OK, new topic: Direct coupled design

Glad to see there has been a little action on this thread. Very cool.

I'm thinking this tube offers good possibilities for a direct coupled design. I've never built one before but I think i'm going to have a go. With both tube sections on the same filament I don't have to worry (much) about one section conducting before the other, and both sections have published data on "lower" voltage operating points.

Granted, a direct coupled design may violate the low $ philosophy of the thread, as direct coupling requires much higher voltage, and high voltage designs are typically more expensive to build. OTOH, I have on hand several PS transformers from old big screen TVs. These transformers typically offer between 130 and 200 VAC and at very low resistance. Doubled, they can produce between 320 and 520 volts. As long as I can swing a good deal on the power supply caps I'm there...

There is a discussion here:
http://www.diyaudio.com/forums/tubes-valves/64604-el84-se-advicenschematics-needed-3.html#post730472
of a direct coupled KT66 design using the 12AU7. Between the published "$250 amp" drawing and this KT66 schematic I think I can get into the ballpark. The feedback design will have to change, but I expect I can figure that out too.

Anybody have thoughts on this idea?

Gary
 
Hiya,

Anybody have thoughts on this idea?
Click to expand...

Sounds like it might work and would be rather nice. Although I am more of a repairer than a modder/designer.

But the logic is spot on and I would love to see if it would be viable.

Frannie
 
I'll have to give it some thought..:scratch2:

But first impression I prefer the cap coupling with how the feedback works
in this circuit combined with UL connected output tube, it works well here..:smoke:
 
Thanks both for the comments.

I'll admit to wondering if it is worth the trouble. I do plan to hook up per the drawing before I start experimenting. I need to get a baseline even if it won't be A/B back to back. Unfortunately I'm working with the Hammond 124ESE, so can't easily duplicate the UL.

If I'm really thorough I will figure out the op points of both sections as DC coupled, but then test with the published circuit at those voltages first. Then change only the topology and see how it sounds.

BTW, there is a nice tube data sheet for this tube with curves at the bottom to be found at this location:

http://www.shinjo.info/frank/sheets/123/6/6LU8.pdf
 
Hi all,

Is anyone running their amp as a pentode, not UL connected. I can get some nifty little OPT's here locally, but they don't have screen connections. Thanks!

jeff
 
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