Elekit TU-8600, Part 2: Building the Kit, and the Lundahl upgrade

In Part 1 of this series, I covered (mainly) the Elekit TU-8600’s performance. That amp came to me fully assembled, as a “Rev.2 prototype”. And in my mind, I’d thought (hoped?) that I’d be able to buy and keep that amp. That didn’t happen. Elekit/VK needed it back, and Victor sent me a brand new kit. So I ended up starting where everyone else would start. Time to fire up the old soldering iron!

What I’ll cover in this part will be the build process, and the upgrade to the Lundahl output transformers.

Building the Kit

How did it go? Overall, I had a pretty smooth experience. There are aspects of this amp kit that are more complex than the TU-8500 preamp, which I built last year – but the preamp had more PCB’s, and tighter spacing overall. So I think going into this amp build, I was feeling “confident” I’d have an eas(ier) time with the 8600, and it turned out to be a little more challenging than I expected. But wherever I encountered a problem, the problem was me. I may not be the world’s worst DIY’er, but I might be the most impatient!

First off, the kit arrived with everything nicely bundled and the parts sorted and arranged into their own bags. Very tidy and professional – no surprise, this is Elekit. The 32-page manual deserves special mention. This is likely the best audio documentation I’ve ever seen. Novice builders especially should take note: look at the little icons on the PCB, look at the drawings in the manual – look for clues. If something seems complex, you’re not looking. They’ve done everything you could think of (and more) to make each step as simple and clear as it can be. There should be any confusion. Just take your time, enjoy each step and try not to race ahead.

You can count all the parts if you like, but the people who package these kits are fanatically attentive to detail, and the chances of encountering a miss are very low. I just started stuffing. My technique was to stuff the board with a full set of parts (resistors, diodes, etc) and then solder that set before starting on the next set. Actually with the resistors you might want to solder some as you go, because there are so many. You just follow along in the order the instructions are written. They don’t always tell you exactly when to solder, but you soon pick up on what’s happening. You don’t want to stuff the entire board, flip it over to start soldering, and have a dozen parts fall out. So keep soldering as you work through it.

The PCB is very well laid out and clear, and in general, there’s enough room to make soldering easy (there are a few tight spaces, but thankfully not too many). “Take your time” is the best advice I can give here. Another general comment: the bigger the part, the more careful you need to be. A part with three pins is a lot more difficult to desolder than a resistor or cap with two legs. The bigger parts become anchored in, and removing them can be a bit of a nightmare.

When I saw this, an expletive was heard as far as neighbouring Oxford County.

I made a couple such blunders. I soldered a seven pin connector into the eight pin position. Bad. Desoldering a part like this involves some brute force, and the part isn’t likely to survive. Of course, the part itself is easy enough to replace. You want to be more careful (while desoldering) not to damage the board itself..a ruined board spells a horrendous amount of rework! Please take your time: as you get deeper into the build you will naturally want to go faster. That’s the time to go slower.

After my replacement connector arrived in the mail (thanks Victor), I finished up the kit – and only then did I notice that the headphone jack wasn’t soldered well. The part wasn’t seated down on the board like it needs to be. ARGH. This means that when you assemble the chassis, the h/p jack isn’t in the right spot where its hole is. Bad. I got it desoldered ok (again with brute force, the part was toast), and finished the build. In hindsight, I should have tried harder to seat the thing. Because unfortunately, the headphone circuit is integral to the amp’s operation: its ‘disengaged position’ allows the electrons to flow to the speaker taps. So, with no connector in place, my amp turned on, the tubes lit up, I could take measurements, but I had no sound – it was as though a pair of headphones were plugged in. Frustrating! Victor said he had an extra Jack and would have it for me at the TAVES show when I saw him there. (thanks Victor)

It’s not the end of the world, as mom would say.

Wait, and wait some more.

So while waiting…well, I got impatient and decided I’d try to paint the amp, for a more funky look. I suppose memories of the red TU-8300R may have been responsible. I thought a red and white scheme would look nice – it would match the bases of the Genelex Gold Lion tubes, and the colours of the Canadian and Japanese flags. (Wall of Sound, Elekit, Japanada. You know what I mean)

Don’t do this. Just. Please. Don’t.

Not unless you know what you’re doing. A metal chassis like this needs the correct preparation before it can be painted. It needs to be cleaned well, with an appropriate solvent, sanded down where appropriate, and primed with the right primer. Even then, there may be issues if you aren’t a pro at applying finishes. I will make a long story short, my ‘test area’ under the bottom chassis seemed to hold up well (sprayed primer and then white sprayed Krylon). But once I sprayed more of the chassis, well, I ran into numerous issues getting the right coverage. In the end, the paint looked ok for a day or two, but started flaking off almost immediately; by the time I had the final part (h/p jack) to complete the amp, I had spent several hours removing the paint. So, my amp is a plain Ellie again, and the colours are a memory preserved in photos. Humbling. I may take the chassis parts to a powder coating place someday and get a nice paint job done. When funds permit. Maybe.

Back to measurements. Initially my readings were a bit of a mess. What you want to do first off, is some careful review (a magnifying glass helps a lot) and touchup of any questionable solder joints. After doing this, I had 37 out of the 38 test points measuring well. However, TP28 was still extremely low, I only had around 0.65V where it should have been 20V. This is the Right channel Ripple Filter circuit – so the result was a hum in the right channel. Victor diagnosed (correctly) that the J13007 transistor was the issue (Q201 position on the board). Removing and resoldering this transistor proved too much, and the part was fried – it then measured 0V. Time for another email to Victor. And more waiting. Victor sent me a new J13007, along with a nearby FET, as well as the new PTC’s that Elekit recommends, since the originals were discovered to be inferior. (thanks Victor)

One correction from what I wrote in Part 1. The headphone gain adjustments are accessible – remove the 300B tubes and the top plate, and you can access the jumpers. I don’t think people will be changing these very often, but if you need to, it’s a fairly quick procedure.

Another thing every builder should do is sand down the chassis to bare metal around the point where the volume pot parts make contact with the chassis. This eliminates any noise related to grounding this part of the circuit.

Et voila! The amp is built, and it sounds fantastic. The build process overall was enjoyable, and of course, it sounds better since I built it myself (grin). Victor gives excellent support – both by email/phone as well as on his forums on Diyaudio and AA. In fact, he had 3 or 4 trade shows almost back to back during this period, and never missed a beat. The man is tireless. There are a few ‘legends’ in the audio DIY business, like Nelson Pass, who continually give and give to the community. I count Victor Kung in that small number who truly deserve our gratitude.

And now….the Lundahl Upgrade

Earlier this year, Victor commissioned Lundahl to make the LL2770 output transformers for the TU8600, as an extra cost upgrade option. My prototype kit arrived with the stock transformers, as well as the Lundahls. I listened to the stock amp for about 4 weeks before switching over. It was hard to wait! But I knew that the chance of wanting to “switch back” was low, and I wanted to give the stock opt’s a fair shake. And to be fair, they are not bad at all. But high end iron is where the bulk of tube amp costs reside, and you can really see that with the Lundahls. You can even feel it when you pick one up, they are close to 6 lbs each according to my bathroom scale. Victor supplies the Lundahls with the parts needed for a seemless installation: bolts, washers, standoffs, as well as custom PCB’s to tidy up the leads and allow the Lundahls to hook up to the Elekit board with the supplied quick connectors.

The photos don’t really do the Lundahls justice. These are big, weighty and robust, they’re beautifully built. They’re designed to extract the last ounce of performance from your 300B SET amp. And I think they do just that.

For me, there wasn’t a night-and-day difference upon installing the Lundahls. What I heard was a subtle, across the board improvement. The bass was a little tighter; the mids a touch more vivid. The top end sparkle was slightly more refined. Imaging ability was a little sharper. Most of all, the music seemed to have a better flow – where at times it was ponderous, it now seemed faster, and more assured. This was especially noticeable to me with modal and ‘west coast’ jazz listening. With better electron flow, the notes and beats are less confused, the music makes more sense.

Again, this wasn’t a super dramatic, jaw on the floor difference. But it was clear and audible. And I think that also reflects my system – I don’t currently have a super high resolution setup. It’s plenty resolving enough for me, but in a more high res context, I think the improvements would be even more apparent. For me it felt like ~15-20% improvement. It was substantial.

Did I switch back? No. And I don’t think anyone else would, either. However, let’s remember that single-ended output transformers are often directly coupled to full range speaker drivers, or to a minimal crossover network – so it is hard to talk about the performance of an opt without considering the speaker coupling. Better iron is better, but I do want to reiterate my feeling that the stock transformers were also very competent. I don’t want that point to be missed. If the cost of the stock amp is stretching your budget, stick with the Elekit-supplied opt’s and don’t sweat it. You will probably have 85-90% of the enjoyment (how can anyone really quantify it?). I’m saying this because, for some of us, another $550 is a big deal. For others, it’s not a big deal, and in that case I can highly recommend the Lundahls. They take this amp to another level, and the cost is well worth it.

So there you have it, it’s a worthwhile upgrade, but not a must do if you’re on a tight budget. I’d rather see someone get into the TU-8600, even with the stock trafos and a cheap set of tubes, than sit it out waiting for enough funds to accumulate. You won’t regret it, either way.

Lundahl LL2770 upgrade: highly recommended!

***************

In the next (and final) segment, I’ll take the TU-8600 out on a road tour, to hear it in better rooms than mine – with better speakers than what I currently have. It may be close to Christmas before I can finish that, I have to catch up on other stuff. As always, we welcome your comments and experiences.