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Old 23rd October 2008, 05:15 PM   #1
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Default building S5 k-amp

I want to build an S5 Electronics k-amp, but they seem to have phased out the k-12 and k-502 that got great reviews, and replaced them with the k-8 and k-16 that get bad reviews. I do not want to spend a great deal of time trying to improve a subpar amp and I am a total novice anyway. Can I still get the k-12 or k-502 from elsewhere? Are there known modifications to improve the k-8 or k-16? Should I be looking at another supplier as well?

Thanks!
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Old 23rd October 2008, 08:35 PM   #2
kmaier is offline kmaier  United States
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Well, as nobody has responded yet, I skipped around the net and found schematics for both old and new... pretty much identical circuitry. It's a simple topology, actually quite similar to the old Dyna ST35 but with lesser tubes.

The new amps are the L series. From an initial scan, these would appear to be better... they use 6005 output pentodes, which are rugged versions of the 6AQ5 which has been used in audio amps forever. The 5670 is also a rugged JAN spec twin-triode. The S5 site shows replacement tubes very reasonably priced and images are JAN spec versions. These are certainly aimed more towards audio than the 11MS8 which was designed for series string filament usage in small TV sets for vertical oscillator and deflection amplifier usage.

I've also seen the site which had nothing good to say about them... frequency response looks poor and power bandwidth non-existant. I would suspect the output transformers are the cause... they're very tiny, and won't go very low... even 100Hz could be a challenge, expecting to see much at 25Hz is more of a dream. Chances are they have high DC resistance and very low inductance.

I would suspect replacing them with reasonable iron would make for a massive improvement. I would also add a bypass cap to the common output cathode resistor. Edcor offer some reasonable low-cost replacements. Something no less than ~8K P-P load should work well. I'm actually tempted to pick one up to play with.

Regards, KM

PS - Tubes and More still shows the older mono version with the 11MS8 tubes... from the tiny image, iron looks to be hammond.
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Old 23rd October 2008, 11:33 PM   #3
cjkpkg is offline cjkpkg  United States
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I browsed at those too when I first started researching a reasonable DIY amp. I did not mind spending a few hundred dollars on the project all together but not all at once. It also seemed that not a lot of folks were not happy with these "out of the box" and there are a lot of sites dedicated to improving these.

So after a little more browsing I found the tubelab Simple SE. It is a great little, simple, single ended amp. There are a lot of folks that have built them and the support along the way here is terrific. It has been a great first time valve DIY experience for me.

You will have to source all of the components yourself but you can get almost everything from a few places. Mouser/Digikey for the caps, resistors, stuff. AES for the tubes and more specialized items. Direct to Allied and Edcor for your iron - just to name a few.

Common setups are a 5AR4 rectifier, 12AT7 driver, and 6L6GC or EL34 or KT88's for driver tubes.

Figure spending 70 misc stuff, 100 on iron, 35 for the board, 60 or so for the tubes and probably throw in another 50 for more misc stuff...~300 bucks for a really nice amp...Less if you really shop and do some good homework.

Just my $0.02
Carl
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Old 24th October 2008, 04:25 AM   #4
chrish is offline chrish  Australia
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I have to add my advice to go with the Simple SE. I have built a copy of the k-xxx topology with 6BM8 valves for my office. It is OK, but I much prefer the Simple SE. The advantage of the k-xxx is that it is a kit, but shopping around for the parts for the Simple SE is really only about half an hours worth of internet ordering, really not a problem. Many here will be happy to offer recommendations for what parts to order.

Cheers,

Chris
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Old 25th October 2008, 04:20 PM   #5
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Default Re: building S5 k-amp

Quote:
Originally posted by watermelonman
I want to build an S5 Electronics k-amp, but they seem to have phased out the k-12 and k-502 that got great reviews, and replaced them with the k-8 and k-16 that get bad reviews.
Can you share the link to the K-16 review.
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Old 26th October 2008, 11:27 PM   #6
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Default K-16LS owner/lover

The S-5 kit performed very well right off the bench for me. This was my first kit. The kit, tone control/pre-amp kit, upgraded caps, and Edcor 25w opt I still came in under $400. I have a set of twenty year old Phase Tech 3way tower speakers. They sound fantastic.
Low end starts clipping at higher volume but is plenty to fill my It sounded great stock but the fun part of diy is tweeking and these kits lend themselves to modding so well. You already have the basics down so the time can be spent on upgrading and learning. The front end caps helped more than the opt upgrade, but I think now that I need to look into upgrading the power supply. There aren't many kits like this one and the people at S-5 are great to deal with. He is an electronics engineer and purchased thousands of these army surplus American made GE 6005 tubes.

In a sound match up against a NAD 743 amp, I may be (and am) bias but the tubes win in sound quality but lose in volume.
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