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I returned to DIY electronics in 2009 after a 20 year pause by building a few kits to get in shape. This blog is for me to keep track of my progress.
Tube power amps
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Velleman K4040 mods

Posted 8th May 2011 at 01:32 AM by alexcp (My DIY projects)
Updated 4th May 2014 at 01:59 AM by alexcp

I posted some time ago a note about my Velleman K4040 amplifier. The sound of the amp as built from the kit was unremarkable and definitely not in line with the price. Lacking experience with tubes, I was looking for some time for well documented mods to the kit.

I found two 2006 posts here and here and implemented them rather directly. The only difference is that I used IXCP10M45S instead of a pair of J508 current sources in each channel and replaced the 1N5408 rectifiers with UF5408 instead of adding noise suppressing capacitors in parallel to them.

The mods did not leave much of the original Velleman design in place; the result, however, is a remarkable improvement in sound!

However, two problems remain: (1) I got hum that wasn't present before the mods; and (2) a two-year old running around doesn't get along with eight hot, attractively glowing tubes. The project is shelved until a better time.

For future reference: The toroidal...
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Old

DCPP aka Engineer's Amplifier

Posted 8th January 2011 at 02:09 AM by alexcp (My DIY projects)

I just built a Distortion Cancelling Push Pull (DCPP) amplifier designed by Peter Millett. It sounds very nice, was fairly easy to build, and is rather inexpensive. Thank you Peter for the great design!
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Old

Elekit TU-879S

Posted 12th August 2010 at 08:24 PM by alexcp (My DIY projects)
Updated 16th March 2013 at 03:02 PM by alexcp

Elekit TU-879S is the best sounding kit I have ever built. Thank you TubeDepot.com for selling these kits. With my DIY full range speakers I mentioned a couple of posts earlier, the sound is fantastic.

Update: one of the original 6L6 tubes got blue sparks inside. As this amp can use KT88, KT66, or EL34 without any adjustment or modification, I replaced both 6L6s with EL34s left from the K4040 project, but the sound deteriorated. A replacement 6L6 from TubeDepot.com restored everything.
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Old

Velleman K4040

Posted 12th August 2010 at 05:53 PM by alexcp (My DIY projects)
Updated 26th May 2011 at 01:54 PM by alexcp

Then was the K4040 from Velleman. Contrary to some reviews, I found this amp sounding rather nice, particularly after I replaced the EL34 tubes in the output stage with separately purchased matched quads. However, the sound does not quite match the price, and I keep this amp mostly for its looks.

Update: I modified this amplifier, leaving little of the original design. See a later post with the details.
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Old

S5 Electronics "L" series tube amps

Posted 12th August 2010 at 05:52 PM by alexcp (My DIY projects)
Updated 16th March 2013 at 02:55 PM by alexcp

I started with a Model 8LS stereo amp from S5 electronics. Very easy to build, nice with vocals, but not quite HiFi. Later I put it into a Hammond enclosure and replaced the tranformers with Edcors. Also, built a Model 16LS, which is the same thing with a doubled output stage, giving a very similar sound. Both use a 5670 double triode in the voltage amplifier and phase splitter, and 2x6005 (4x for the 16LS) in the PP output stage.
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