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

I've ran it in Triode, UL and Pentode, does perform best in UL, but both
Pentode and Triode are options, in pentode I would make that feedback
resistor smaller say 100-150K, in triode either do away with it or go 470K.
 
Ok, thanks Keg. I think I'll go ahead and order the OPT's and experiment a little. This amp will probably be for "desktop" duty, so triode mode may work out just fine.

jeff
 
Has anyone implemented a volume control?

I'm using your basic 100k pot to ground as a volume control on this project, but I get a high level of distortion at anything but full volume. Anyone experience similar? Also, what is the sensitivity of the amp when built as drawn? Is it somewhat low, or does a typical CD player drive it just fine?

Gary
 
It is basically a full 2v input to drive the amp to full power/clipping. (all of cd output)
(If need more sensitivity/gain put say a 220uf bypass cap on the drivers cathode res)

Don't know the source of the distortion, but almost sounds like a bad pot or miswired
maybe? (just guessing here), but a pot shouldn't have any bad effect.

If I were running a 100k pot, I'd replace the 270k input resistor with 1 meg and install
the pot at the very front of the amp leaving the 1meg an 500ohm grid resistors intact.
 
6LU8 PCP about freaken time :-)

After months of begging by my... my friend, MR. Chong (Tubes4Pro) decided to finish his 6LU8 SE PCB.

The build quality is excpetional. I have mine... 1st off the bench running on my Cornscala's.
Per Mr. Chong, its 5watts and is running the tubes very conservatively. Any questions, PM me..

I used in this build:
XPWR009-120
Power transformer (275-0-275) at 175mA center tapped, 6.3V at 4A and 5V at 3A.

GXSE15-8-2.5K
15W, single ended tube output transformer for 2.5K Ohms to 8 Ohms



I already have some of the XSE transformers ordered for the next version.
 

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That is cool Justin, (I did a minor edit to your previous post)..

Couple questions for you,
Is that the same exact circuit as the 1 designed here?

And any reason in particular why you went with 2.5k primary?
 
Kegger,

I believe it's similar but not the same. Mr. Chong hadn't written up his schematic yet. When I get it, I will post. 2.5k was just what we had. He had suggested 2.5 to 5 k would work. Im not sure as to his reasoning.

The P2P/Turret version I have uses 5k and outputs 6watts. Its interesting... 2 similar amps, but somewhat different approaches, equaling very positive results.


The pcb stuffed is ~ $ 85. Super cheap in my mind. P2P was over my head. I went after convincing Mr Chong to get a pcb running becuase I saw a real interest in the tube. Sparetimegizmos and tubesforhifi did the same for the 6t9 putting it on a pcb helped many enter the SE world.
 
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Kegger I think one of the main differences is the feedback network. The PCB uses the transformers for feedback I believe. As soon as I get a schematic, Ill post.
I brought the amp over to a friends and we put it on a load and measured output vs distortion... 5watts... very very little distortion... the Amp did really well and was able to maintain its output without serious dropoffs. Wonderful to see... I guess a product of feedback and good transformers.
 
With these Edcor transformers an there high frequency performance you can
certainly use LOOP feedback(from the output side of the transformer back in)
and it will be stable, my main design with these single ended amps is the use
of the UL taps and Local Feedback,(schade style) then loop isn't "needed". :)

I prefer not to use loop feedback when the design warrants it, from both the
technical aspect, and I prefer the sound without loop feedback, but one sure
can use loop feedback if they want to. ;)

Also using a higher primary, 5k verse 2.5k, will need less feedback to "control"
things, there are multiple ways to get the end result, one isn't necessarily any
more proper then the other, it often comes down to ones design philosophy. :smoke:
(again here though, at these voltages and currents, 5k is still the better load)
 
We've done distortion measurements. (on the original)

And have checked frequency response of the smaller edcors, what I wouldn't mind seeing
is a frequency response graph at 1w an 5w with the bigger edcors or other outputs even.

When I say bigger edcors I'm talking the Gsxe line like these..
http://www.edcorusa.com/products/537-gxse15-8-5k.aspx

You'll also get best power and distortion with 5k primary verse 2.5k.
(just stating for testing purposes)
 
Hey Kegger, it's been a while..Well, I've finally Hooked this into 94dB Klipsch Kg3's...And it sounds Nice...But, maybe a Tad Bass Shy...I'm thinking of Kick'n it up a Notch with a Pair of these Edcor OPs that will go down to 40Hz, not just 70Hz like the XSE15-8-5k's on there now....Do you think I'll be able tell the Difference?...

http://www.edcorusa.com/products/509-gxse10-8-5k.aspx

Or, will I need These....Which will be a Larger Notch Up...

http://www.edcorusa.com/products/537-gxse15-8-5k.aspx

Either way, they will Look Way Better....
P.S. I didn't check your Link till now, to see that it was just what I am asking you...
 
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Your basically asking what I said in the post just above yours.. :)

(but a good question none the less there Sled)..:thmbsp:

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

And yes I've heard both the original smaller guy's an the GSXE line,
I'd go with the GSXE 15W, like these, and yes I believe you'll tell..:music:
http://www.edcorusa.com/products/537-gxse15-8-5k.aspx

Or the 10K to 16ohm using 8ohm speakers for the 5k primary..
http://www.edcorusa.com/products/544-gxse15-16-10k.aspx
(If I were buying new in this series I would probably get these)
It's been posted on the net you will get higher inductance(better bass)
with using those Edcor 10K to 16ohm but using an 8ohm speaker there.
(from the info I've seen it looks correct and understandable/predictable)


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

Also the original 70hz ones rated at 15w go lower at our 5w output here
but the GSXE will go a bit lower and with less low frequency distortion to.
 
Sorry Kegger...I Pasted the Wrong Pages...They should be right now..And, Thanks..You've told me what I wanted to Know...It's time for the GXSE15's...Or, the 15-16-10K's...Oh Jeeze...Decisions??
 
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Yep you got um, and you are welcome, post up when you do it, I'll be interested in your thoughts.
 
Alrighty Then..Lets put it out There...What about using 16 Ohm 10K OTs with 8 Ohm Speakers on a Rig like this??

Wanna Bet that you're the only One who Knows about this, Kegger?
 
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If you don't feel right about it in the end, just get the 5k to 8ohm.
(but it's pretty standard ratio stuff, the inductance is the "bonus")
 
Oh, and BTW...For any One Watching, this would be a $100 W/ Shipping 'Notch Up'..
($50 increase if you subtract the originals from the start for a first build)

Which, would make It a '$300 Amp'...Maybe....And, Well Worth It...
 
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