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KT88, (ect) Single ended amp, SEUL

Kegger

Kegger

R.I.P. 1/12/1966 - 6/1/2017
I have been asked several times for the layout of my "KT88" based Single Ended amplifier.
(it's a circuit that I've been using and refining for a while now) :) (updated again) 2015

This is for KT88 based Single Ended Ultra Linear amp using very good output transformers.
(this is the circuit I use, it has performed extremely well, even on cheap outputs).. 11wpc

I'll give a bit more info that may help some that are interested to build what I've suggested.
http://www.audiokarma.org/forums/index.php?attachments/kt88_se_ul_400v_6ej7_actual_m1-gif.585164/

A 1k pot/560ohm in paralell in the drivers cathode circuit can just be 130-200ohm resistor. (now 180 ohm)
(R5 can be 1-4.7k 2w) (C2, C5 450v rating or higher) (R3 1w) (C3 100uf-470uf 50v or higher)
All other unmarked resistors can be 1/2w rating. (C1 400v rating or higher) (R12 use 1.2-1.5k)
(If taking the B+ up near 500v use 160-200ohm driver cath resistor and adjust R5 for voltage)

This amp can run from EL34 through say KT120, (which means 6L6GC, KT66, KT88, many more)
(use an smaller first cap in the supply and keep the voltage to <401, 807 types can run to). ;)

The driver's a 6EJ7/EF184 per channel triode strapped, there's quite a few tubes to roll here to.
http://www.audiokarma.org/forums/index.php?attachments/pinout_xcon-gif.270997/
(there high transcon signal tubes)

A little more info at this post:
http://www.audiokarma.org/forums/showpost.php?p=4600316&postcount=8

I'm also including a power supply for a stereo amp, including the power transformer an 2 chokes.
(I would run parallel 5V4 rectifiers, can use a single or parallel 5AR4 as well)

"450-475v of B+ is a good place to be with a cathode biased KT88, but power supply
caps get more and more scarce at those higher voltages needed with that much B+.
(and you'll be pushing EL34's and 6L6GC's if you want to swap them in as well here)"

If taking the B+ in 500v range you'll probably want to use 560ohm+ for output cathode resistor.

The first/10uf cap, I'd suggest an Solen 630v poly cap there. (2nd cap, I run between 180-470uf)
Other caps in the supply chain can be 450v electrolytic's, an you may want to bypass like schem.
(you don't have to run the .33uf bypass caps, all electrolytic's could go 500v rating if you like to)

The Solen 630v caps can be gotten from many places but these guy's usually have nice prices.
http://www.partsconnexion.com/

If wanting to do mono blocks, replace the 10uf Solen with a 3.9uf and use a single 5V4 rectifier.
(you could use motor runs or some other oil types as well, even other brand's of poly's)

Power transformer:
http://www.edcorusa.com/products/589-xpwr002_120.aspx

Output transformers: (can build with cheaper, these are VERY nice)
http://www.edcorusa.com/products/476-cxse25-8-5k.aspx

These would be the cheaper ones, (to save a bit of cash, still nice)
http://edcorusa.com/products/537-gxse15-8-5k.aspx
Or these
http://edcorusa.com/p/530/gxse15-6-5k (to cover a wide range of speakers)

Choke 1: (this choke would mount top side)
http://angela.com/hammondchoke193h.aspx

Choke 2: (this choke mounts underneath)
http://angela.com/hammondchoke159v.aspx

As I get more time I'll give more details. (or things I may have missed).. :smoke: (voltages are "reference", don't need to be "exact")
------This design can scale up to 500v, 450v would be good, just watch capacitor voltage ratings and up them accordingly------
KT88_SE_UL_400V_6EJ7_M1.gif
UPDATED 2015..
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Thanks, It's something that's been meaning to be done for a while. ;)

--------------------------------------
(I've added the following to the original post)
The Solen 630v caps can be gotten from many places but these guy's usually have nice prices.
http://www.partsconnexion.com/capacitor_film_solen.html

If wanting to do mono blocks, replace the 10uf Solen with a 3.9uf and use a single 5V4 rectifier.
 
Hiya,

I wish that some day these builds would be consolidated into a master sticky at the top.

Just a index is all.

Kegger, awesome build and thanks!!

Frannie
 
Not a bad idea Fran.

The User CP keeps track of any uploads you've done,
maybe I'll try and at least consolidate mine sometime.
(that way I can try to answer questions on them) :)

--------------
 
Great stuff Kegger... want to thank you again for your willingness to share with the diy community. Stan
 
Wow! What more can a person ask for ?
I've learned and benefit greatly from your helps in my SEUL built.
Thanks Kegger!
 
Thanks Keg!

Now if we could get a Sam's photo kinda thang that shows where everything goes for us folks to slow to read schems :D
 
what primary Z are you using? I'm running KT90s in my SET amp, but no UL taps on the Heyboer OPTs. Should have had them put some taps in.
 
Kegger said:
Not a bad idea Fran.

The user cp keeps track of any uploads you've done,
maybe I'll try and at least consolidate mine sometime.
(that way I can try to answer questions on them) :)

--------------
Click to expand...

Hey hey hey...your prototype had one rectifier tube...I was looking forward to seeing two in parallel... :D

-D
 
That was the prototype amp, it used a different supply configuration that
couldn't be reproduced with off the shelf parts, so I put one together here.

----------

There is pic's of my parallel SEUL 6LR8 amp an push pull triode 6AV5 an
dual rectifiers, I go back an forth on the amps with 5V4 and 5AR4 rectifiers.
(there's a separate 5v filament tranny for the 6LR8, so I can run GZ37's to)

Sorry no real good top side shot of the 6AV5 amp really showing the 5V4's.

The 6LR8 amp you can see them easily though, flanking the old 70 chassis.
 
I can't wait to get the money together and round up the parts to build one of these amps. Been wanting to do it for sometime now.
 
I see lots of threads in the guitar world about the sound and tonal quality differnces between say 6v6 or EL84 and EL34 or 6L6. I don't see as much from the Hi-Fi threads, wondering if the tonal differences are not as distinctive here?

So in a SE UL configuration like this with EL34, 6L6GC, KT88 or whatever... is there a distinctive difference in the sound compared to say an EL84 or is it primarily just for more power? If blindfolded and the amp set to put out the exact same dB level can you identify which tube you are hearing? If so by what quality?
 
Thanks Kegger. I have a question about the feedback resistor 200k used in your design. I want to try this on my SE Abdella design amp. After placing RC filtering in the B+ supply for the driver tube, doesn't adding the feedback resistor to the B+ of the power tube allow "less filtered" B+ to get to the driver?
I'm just trying to understand this as I currently do not have any feedback in my amp, but want to try it.

Thanks
Glenn
 
I run this circuit and really like it! Works great with my KT120s too!

Nice choice in chokes there Keg. It's nice what we have available brand new.
 
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