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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Review of New S-5 K-16LS Kit

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It's a piece of plexiglass that has been painted black on the back side. It ended up being really reflective because of the shiny top with matte back. The hardest part was cutting the holes with a hole saw because when it heated up even a little, it would stop cutting. I ended up having to dunk the tip of the hole saw in ice water every 10 seconds or so to keep it cutting.
Hi, Excuse me if I laugh. I've been there too. The one project (Oddwatt) amp used 3/8 inch thick high strength plexiglass. Oh fun and games. Part of the way I finally did it was to slow down the speed and drill a little on each hole then move to the next until all six were done. I now use a drill press and real slow (500 rpm) speeds to drill things like that.

Nice job finishing on you part.

Keep up the good work, have you had a chance to hear how the amp sounds? If so with what sources and speakers.
It sounds suprising good for being a lower priced kit. I am enjoying the sound except for a bit of a hum which I should be taking care of this week (and hopefully upgrading a little :D).

I am using the amp for my computer rig, so it starts with my Vista PC using lossless files. Optical out to a AMC 8 DAC, plugged into an Adcom power center. My speakers are a pair of Polk Monitor 5Jrs that I upgraded with RDO silkdome tweeters and rebuilt the x-overs using Mills and Jantzen components. The speaker cables and ICs are star quads that I custom made.

Also, I was looking at rolling tubes on this amp since I just have to stock 6005s. I was eyeing either EL90 or 6AQ5, but am open to whatever. Do you know what are high quality tubes for this application since I'm sure the ones that came with the kit aren't exactly audiophile.
Hi, I'm not up on that particular tube type. Someone out there may have some thoughts on them for you. I'll ask as well. Sounds like a pretty good set up for that amp. The hum can be tamed to reasonable levels without a great amount of work or cost. The stock hum levels in the K-12 series was bet 5 and 10 millivolts at the speaker. It can be brought down below 2-3 fairly easily. Below that requires $$ and effort.
Just finished my S-5 kit


The stock K-16LS sounds fantastic. I am eager to see what it will do when tweeked. My amp is driving two 8ohm PhazeTechs very well I don't hear much hum and there is zero buzz. It may be the position of the output transformers at this time. Restoring pinball machines is my main hobby but this may take over. I have ordered the upgraded output transformers from Edcor. wonder what type of improvement the bridge mod does. I don't have any diodes of that size in house but was wondering if 4004s would work. I will take on the cap upgrades next and then design my chassis to expose the "goods". It's great to know that there is such a deep base of knowledge out here.

Thank you all for your input.

Hi, I'm glad the amp is up and running and you like the sound. I would not bother replacing the stock rectifiers with 1N4004s. No real improvement. Fast recovery rectifiers are available from several sources and are really cheap. The biggest problem is the associalted packing and shipping fees most companies charge. Which Edcors did you order? I found the best improvement in most of the tube amps I have worked with is to replace the interstage coupling capacitors. The most dramatic was in the K-12. Since then, I usually start with good caps and save the step. Power supply mods will help with the noise floor and bottom end as well.
Edcor 25w 8ohms (CXPP25-8-5K)

There is a two week wait for my opt's from Edcor. They are the 25w 8 ohm "cutties" you have parked on top of your very cool Oddwatt 225. Can I go through Mouser for the Gold caps or is there another place you would recommend? I went to the Goodwill today and found my box and chassis in the form of a $2.99 brass serving platter and some scrap poplar hardwood. Pics soon. Again, I just can't get over the sound that is produced through this amp. The strings! I can hear the fingers hitting the strings as they play. Is it my imagination? or have I been listening to crap all these years? I am going back through all my music again and nothing so far sounds the same.

Thank you for the heads up on high voltage. As someone who has experience underneath a pinball playfield I do understand the dangers involved.

Take care,
Hi, They should be a good match and will allow for some experimentation on selecting a load tap for your speakers. Not all are as they claim. I usually get my parts, from Parts Express, MCM, Antique Electronic Supply, Digikey or Allied. Mouser is also good. Check prices and shipping for the best deals.

Your choice of chassis seems interesting. I find many such things in the kitchen section of department stores. I will be posting some new projects in a couple of weeks that use wooden (bamboo) kitchen organizers for chassis.
Well friends, I just installed the 270K bleeders for the fun of it and the .01uF cap on the HV wires. Unfortunately, that didn't get rid of any of the buzz, so I will be upgrading the filter caps next and looking at the diodes. Also, maybe trying some snubbers across the filaments of the tubes.

At this point, I'm just having fun trouble shooting this project and using the oscilloscope to look at the buzz and oscillations.
bayermar said:
- I paralleled the HT cap (C10 in your schemo) with a Solen 22uF PP film. Hugh improvement in detail (Highs, but also in bass - maybe a case of placebo, since I have no switch to go back and forth). Even if Placebo, I liked this mod very much.

Would this be necessary since I am replacing all of the filter caps with higher quality and larger value caps? I know when I have rebuilt speaker xovers in the past I have omitted bypass caps because they became irrelevant with high quality caps, and just ended up sounding unnatural.
Osciliscope testing?

I have a Ballentine scope and have no idea where to connect to find where my drop off is. Also, if I have to lengthen my transformer wires, do they need to be shielded?

I am already thinking of the next step and wondered if I am better off building another 16LS or are there plans out there to make something with a little more meat. What do you suggest?

Thank you again for your advice,
Hi Jake,

with regards to the caps in the power supply.
It really depends on the caps you are using and how you like the sound.
In my case, I like the sound of film caps more. If you use motor run caps in the power supply there will be likely no need to parallel that.
In case of electrolytics I find there is a noticeable change if they are paralleled with a film cap (I'd use 1uF polypropylen film, I just had this 22uF monster lying around, tried it and liked it).
I'd put the cap right between the output transformer center tap (B+ tap) and the cathode ground if possible.

It's cheaper :D
The idea is to bypass electrolytics with a small film to get the combination closer to an "ideal cap".
To my (not so critical) ears there is a limit in the size of the film cap where there is a noticeable change as long as you don't replace the electrolytic entirely.
1uF worked fine for me and they are not so expensive.
Some people get rid of electrolytics entirely and use motor run caps.
That's a different story.
As I said I had the 22uF lying around and I liked the result. If the size was necessary - I doubt it, but it sounded nice so it stayed there.
I never made really systematic experiments there.
Sorry, that I can not give a clear advice other than try and see.

Mounting the pots underneath (K-16LS)

Is there a problem that I am unaware of in remounting the the potentiometers under the board. I understand that they will be reversed but I am pretty sure that these pots or not polarized but I like to chech with smarter people than me. I am having a hard time trying to fit my knobs in through without running wires from the board to the box. I will use something a little less difficult to work with besides brass on my next project.That is what I get for trying to make a silk purse from a sow's ear. I am using Molex connectors from the circut board to the transformers and preamp so they can be serviced quickly just by plugging in and out each component.
Amp enclosure

Here is my finished amp with the tubes exposed. I really had fun building this kit and enjoy listening just as much. Thank you to all that shared there stories, ideas and comments.

Here is a pick of the end product. I am still waiting for the Edcor opt.

Savor the Music,


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