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KT88, (ect) Single ended amp, SEUL

cubby01 said:
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?
Click to expand...

I would say for the most part yes, there is a pretty "distinctive" difference between say an EL34 and a KT88.

The KT77 is another that differs an fair amount to be heard, even more so in single ended circuits, along with
the drivers, even more I'd say with the drivers, quite often even the rectifiers still in single ended amps as well.

So yah with this particular amp where you can roll many drivers, outputs, an even rectifiers you can tailor a lot.

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

We are having rolling blackouts here and I've got limited time online, so my responses are slow for a bit here now.
 
vfr800fiman said:
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
Click to expand...

Actually you'll more then likely get more filtering through that feedback path then the RC stage
provides for the driver, if you follow the B+ you can see it goes through the output transformer
before it goes through that feedback resistor, so in essence the output is looking like a choke as
well, which is one of the reasons I stress clean supplies before the output transformers get there
power so they don't have to act as a filter and an output transformer, but alas since the voltage
does pass through them they do to some degree anyway.

And the RC stage for the driver I don't really use as a filter really but more just for decoupling from
the output transformers power supply section, but yes it does do additional filtering, filtering there
is more a byproduct really then a need as long as you build a pretty clean supply leading up to it. ;)
 
Thanks for that explanation. I added the 200k feedback resistors to my build, and so far I like it. I've been running EL34's in Pentode mode, and it did make a difference in the distortion. This is by ear only, but I do hear a difference. I like Pentode mode for the added power.

I'm going to put the original Sovtek KT88's back in and see how they sound in Pentode and UL. Any point in trying Triode mode with either EL34's or KT88's?

Thanks for posting this schematic, it's made an improvement in the sound of my amp.

Glenn
 
Yes try all modes, some like pentode, some like ul and some like triode.

Myself with a proper driver tube, running with the plate to grid feedback
I prefer UL, whole combination works "extremely" well together as far as
sound and technical performance from this circuit.

This driver/feedback circuit with running in UL has been "tweaked" on in.
(if running the outputs in pentode might want to use 100-150k feedback)
 
The power supply schematic was right on the first post.
(server redo lost it, but the parts for it are still there)
 
And, so it is. Thought I'd opened all the links. Have read so many threads on this I'm starting to lose track. Think I'll print everything for reference.
 
I wired my 6EJ7 in pentode.

G2 regulated at 102v(2.5mA) with 2X IN5369B and bypass with a 10uf oil cap.
 
Hi Kegger...Looking at your Schematic brings me back the the 6LU8 days...Hmmm...Starts making me think of a KT88 SEUL project too...
 
I've heard these amps and I can tell you from personal experience that they sound great. Those gray 66 really kick butt.....best I've ever heard.
 
Kegger said:
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
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
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:
------This design can scale up to 500v, 450v would be good, just watch capacitor voltage ratings an up them accordingly------
Click to expand...

Am wondering if this transformer 'set' work for this application? Understood that still need the larger choke from Edcor.
http://store.triodestore.com/mk3trbuwfrch.html
As I put together my BoM for the build I'm having the most difficulty with the chassis. With this set, can purchase the matching, pre-drilled/punched Dynaco MKIII chassis as well as the proper number of tube sockets and I/O connector holes, etc.
 
MX117.MC7150 said:
Am wondering if this transformer 'set' work for this application? Understood that still need the larger choke from Edcor.
http://store.triodestore.com/mk3trbuwfrch.html
As I put together my BoM for the build I'm having the most difficulty with the chassis. With this set, can purchase the matching, pre-drilled/punched Dynaco MKIII chassis as well as the proper number of tube sockets and I/O connector holes, etc.
Click to expand...
I'm not sure if they'd work. If they did, they wouldn't be ideal...

Those output transformers are designed for push pull use, and what you need here is single-ended with an ultralinear tap.

The Edcor transformers that Keg linked to in the original post are really excellent for the money, though I don't know if they'd drop into the chassis you're looking at.
 
Yes....... I've downloaded the drawings of the transformers and am doing some "hole matching" and layout overlays to see what will/will not fit. Thanks.
 
YAY!

I have a pair of Mullard EL37's collecting dust just ITCHING to be used . . .

you rule Kegger !
 
I finally got around to getting this wired up. I don't have the UL opts I need yet so used opts I had and wired the output for triode. The Edcor's are on order.

As you can see I've got a lot of room here but wanted something easy to get around. Someday maybe when I feel more confident I'll make it pretty.

I used a different power supply than the OP and have more B+ than was called for. For this initial test I threw on some coke bottle 6L6s and used the variac to dial it down. Right now I've got some EL34s in it.

scaled.php


The underside is a bit of a mess and probably generating a bit of noise that I'll need to work on. The opts I have on order will go on top but I used the space underneath for now to avoid unnecessary holes.

scaled.php


Thanks for posting the circuit Kegger.
 
With the original schematic and using KT88's you can scale to say 500v without issues.
(that is as long as your supply caps aren't at or over voltage that you used)

Just check plate voltage on drivers, may want to lower cathode resistor and adjust R5.
(also watch current on the outputs, may want to up cathode resistors to say 560ohm)

450v should work well with 6L6GC's or EL34's, curious what voltage do you have there?

---

Any-who nice looking build! :)
 
Last edited:
avoid the tomiko toroid SE outputs! they suck!

the EI stuff is good though... although I don't think it's any better than Edcor.
 
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