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Ben's K-16LS Tube Amplifier Kit - review and scope shots
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Author:  Bennybuis [ 08 Nov 2009, 09:28 ]
Post subject:  S-5 Electronics K-16LS Tube Amp Kit Schematic

Hallo everybody, I was finally able to make a photo of the schematic, good enough, I'll post it now.

Author:  Bennybuis [ 08 Nov 2009, 17:04 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Hi everybody,

I have a probably stupid question. Running the amp without load or with little load (32 Ohm headphones) won't hurt it, will it? Especially at night I hook up my cheap Sony headphones and enjoy the tube sound. I have some experience in the RF technology and I know you should never turn on a transmitter without a properly matched antenna otherwise you'll screw up the output transistor. Greetings from Holland

Author:  Gio [ 09 Nov 2009, 00:28 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Ben, take a look at the operation characteristics on page 4 of the datasheet:

Using 32 ohms instead of 8 is going to increase the load resistance by a factor of about 4. That is going to put the load off the plot, but you can see the trend for distortion and current.

Author:  Bennybuis [ 09 Nov 2009, 07:05 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Hi everybody,

well the distortion factor by using headphones (32Ohm) is at least with my ears not to hear, sounds good to me. And I am very difficult, it has to be perfect, I hear everything. I never had a 4 Ohm load on my amp, I simply don't have 4 Ohm speakers, but in combination with my Bose bookshelf speakers (Bose 201 Series III) this amp sounds really really, really good.

Author:  nights [ 10 Nov 2009, 23:44 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Interested in getting this kit, but I've got concerns on a few things:

Can you use it as a preamp to connect it to an amp instead of speakers? I plan on connecting it to Cambridge Audio Azur 650A amp.
Also, how much bass does the 16LS add/remove? I've got pretty small bookshelfs and they're not bass heavy and adding a preamp with a more treble heavy foot will mess up with my current settings. (hopefully someone will know what I'm taking about =)).

Cheers, and thanks for taking the time and running the amp through a scope app. It's helped me narrow down my choices for my next kit =)

Author:  Bennybuis [ 11 Nov 2009, 11:42 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Hallo, I am running that kit on 8 ohm bose 201 series III bookshelf speakers and it sounds really good. The kt has been great so far, even though I find more and more things that need improvment. Anode voltage right and left channel differs 14 volts, you don't hear it, I don't like it, that is to fix with high grade resistors. I bought today all the resistors new with very little tolerance and I will exchange 'em all. I was today in the local electronic supply store, spent about 100 bucks but didn't quite get what I wanted. I went there for some fast bridge rectifiers, no go. I couldn't get any 0.22 uF caps at all, please guys, help me out on this one, I only need a few, but I want some good ones, I don't have no experience on that either, so somebody who does, please help. Anyway, I bought myself some 8 ohm resistors 25 watts. I didn't know they make those, but now I can bridge the output for listening with my headphones. Works great. Anyway, once I have the caps exchanged and the output transformers and maybe get the amp ultra linear to go, I will know if the kit is good. Until then, its a pretty decent class a amp, not more, not less.

Greetings from Holland.


Author:  Bennybuis [ 02 Dec 2009, 20:29 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

I ended up with a second pc-board for my kit, so I started putting a "GOOD" and improved version together. I don't know, maybe I will start a new topic? I don't know.

All the resistors are matched metal film with less then 1% tolerance between each other and with less than 1 % of their value. So that is about as good as it gets. Also the stock 150 Ohm 2watt resistors got real hot. I exchanged them with 6 watt resistors. That should keep them cool. In the posted picture you will notice that the 8 screen grid resistors of 200 ohm are missing. That is because I won't need those anymore, I have new output transformers from Edcor coming, I hope this week and they have the 40% UL tap. Those connect to the pentodes at pin number 6, where the stock amp just gets screen voltage via the 200 ohm resistor. Do I have to put those 200 ohm resistors between the screen tap and the output transformer or not? Does anybody know?

Otherwise I just gonna try both possibilities and go by the better one, if I can find out that way.

Anyway, it's been a good kit. Things I didn't like I am gonna fix now. For example the plate voltage differed between both channels 14 volts. No big deal, I don't like it. That must be due to the resistors and must be good now, haven't tested it, yet. Another thing is that the stock pot is just bad, right channel starts way before the left. Better quality pot will help that, too, I hope. Pot is already exchanged, but not tested, yet. Hum. Not much, still, too much. That can be everything. The amp is rather clean, but it does have a tiny bit of hum, which could be due to the ac heating or the filter caps. Here is what I am gonna do. I am gonna rectify the filament current with 2 6 ampere rectifiers. I will put those rectifiers direct into the lead of the power transformer, to have only very short lines carry ac current. That fix will also fix the filament voltage issue. On the stock amp, the filaments are only heated with 5.4 volts. In my opinion, just enough, but other well respected members told me, NO not good, so by rectifying the ac current I should get somewhat around 6 volts, good enough for me. That fix hasn't been tested either. Coupling caps. I have no experience with coupling caps, but I desperately need some experience, so I decided to have one channel with the stock caps, temporarily, of course, and the other channel I will use to experiment and change caps to find out for myself what I like. If anybody has any better ideas,please let me know. One thing I am a bit unsure of are the 6 watt resistors I am using now. They are matched, alright, but they are also inductive. (Wire coil) BUT they are just the ground resistors for the cathodes, so no signal through those babes. Will they work? I am just about to find out. To rectify the heater current already in the transformer leads must be a good one, I think. I could do that with the primary as well, just that it is not center tapped and needs a bridge instead.

The kit is still my best sounding amp so far. The improvements are not gonna make it worse. Despite it's reputation, it's a good kit and for the money worth trying. To be honest, I learned so much about tubes that I would not buy the kit again. I would start from scratch this time. But without this kit amp I would have never found the love for the tube and I would not know, what I know now.

Once I get the Edcors, I will put it together and run some more scope tests.

Author:  Gio [ 02 Dec 2009, 21:41 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Hi Ben, the pot that came with my kit died shortly after I put mine together. You may want to try something better like an alps blue velvet.

Author:  Bennybuis [ 02 Dec 2009, 21:53 ]
Post subject:  Re: Ben's K-16LS Tube Amplifier Kit - review and scope shots

Thanks Gio,

I already replaced it with something inexpensive from my local supply store. (Bad store, no caps) It works good right now. I found an audiophile diy store 40 miles (about 60 kilometers) from my house, here is the link: That is also where I got my fancy EEC802S from. Check it out. If you want something, I go there next week.


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