ELEKIT TU-8900 2A3/300B (Stereophile Review Available NOW - July 2023 Edition)

Today Jim can find his TU-8900 after the Califorina Fire.

Jim don't worry your replacement amp is ready to go...
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Trying back and forth with two different tubes in my Elekit 8900 today. Tubes are WE300B and a pair of NOS Sylvania 2A3 from 1945. To complicate things a bit is that I can choose to disable Negative Feed Back in the amp.

WE300B
First thing that struck me was the amount of bas it delivered! Very, very deep and strong. Mids and highs still was there but on some songs the bas was a it owerwhelming. Varm, nice and a bit ”wild” but not the most articular sound. Enabling NFB enhanced this. Brought the bas to normal levels and making it much tighter. I think I prefer it this way? Not sure yet since it sounds very different with different kinds of music.

2A3
Here you have a lot of that ”tube magic” people talk about. At least this is what I think it’s all about…? Listening without NFB there is plenty of air. It clearly reproduce the sound and space in the room where the music is recorded. It’s not artificial but songs recorded and mixed that way will absolutely benefit from the 2A3. Every instrument is clearly reproduced and easy to identify. Vocals feels a tiny bit lighter maybe? But all the micro details in the music makes the soundstage wider and higher. I have never understood how two speakers could give a feeling of height. But if the recording has these room sounds and fine details reproduced I think that the brain might interpret what it’s hearing as reflections from a roof? Not sure. Just a guess. Anyway it works. Enabling NFB tames the sound and take away a bit of its charm. No NFB is preferred in this case.

2A3 is here to stay. But still deciding upon those WE300B? It’s a bit like a big powerful American SUV. Does anyone really need them? Probably not - but they are quite fun!

P.s
Wife got home to work in her home kitchen so I put my headphones on. And lo and behold - further changes to the sound. Suddenly the 300B:s sounded great without NFB. Strong bas but not to much (as with speakers). A quick listen to the 2A3 didn’t reveal as big difference between the tubes as w speakers. Interesting.

I’m sure some of you clever diy:ers can explaine. Now - more music!😊
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the most articular sound
What kind of speakers are you running? Are you familiar with or can you look up the impedance curve and or phase angle of your speakers? Speaker sensitivity is only half of the equation. Higher sensitivity will give you more output, but even sensitive speakers with wildly varying impedance curves with low dips present a very difficult load for a low power SET to control. This results in woolly bass. Negative feedback will enhance that control slightly, but you lose the SET magic.
 
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What kind of speakers are you running? Are you familiar with or can you look up the impedance curve and or phase angle of your speakers? Speaker sensitivity is only half of the equation. Higher sensitivity will give you more output, but even sensitive speakers with wildly varying impedance curves with low dips present a very difficult load for a low power SET to control. This results in woolly bass. Negative feedback will enhance that control slightly, but you lose the SET magic.
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I found this…
There are other speaker parameters beyond my scope, but it looks like a reasonably good load for an SET. The speaker impedance looks like it’s averaging about six ohms. Have you experimented with the speaker output impedance switch? I’m going to guess you have. It may tighten up the bass a little bit.

May I ask the brand and model of the speaker?
 
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Yes, I think they are a good match for horn speakers. Speaker is Avant-garde Zero TA (I think it’s ”TA” - anyway it’s the variant with only bas active).

I’ll try some more with 4 or 8 Ohm settings. I’ll had it on 8 since I thought that speaker was at least 8 ohm impedance. However this test shows that 4 might be a better match. Or?
 
There are other speaker parameters beyond my scope, but it looks like a reasonably good load for an SET. The speaker impedance looks like it’s averaging about six ohms. Have you experimented with the speaker output impedance switch? I’m going to guess you have. It may tighten up the bass a little bit.

May I ask the brand and model of the speaker?
Just arrived back home after a business trip and immediately tried the 4Ohm setting. During “normal” listening level it sounds really beautiful. I’ll do some more extensive listening tomorrow. But what also struck me was that I can somewhat choose the level of distortion of the tubes. If the diagram I saw on the we300b tube is correct the level of distortion is very dependent on how far you push the them. Will do some more tests.

My plan was to use this amp in my office but it ended up, and will stay, in my living room.However I ordered another kit today which I plan to take to maybe a higher level. This time amourphus Lundahl transformers, some better resistors, stepped volume pot and Audionote Silver coupling caps. It’s hard to believe it possible to take the sound even further but ill give it a try!

Sure going to be interesting to compare them.
 
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Capacitors
Might want to research the different dielectric types.

My personal preference is V-cap CuTF. I also quite like the Odam caps—though not as impressive looking being considerably smaller. Odam might be a fun swap in your original 8900 if you used the stock. Depending on personal preference and the amp, you might even like the Odom better than the CuTF. Price generally is indicative of quality, but may or may not be indicative of ones personal preference. YMMV.
 
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Thanks. I understand that V-caps are very popular. If I remember correctly Stereophile reviewed an 8900 with Audionote. Problem is that there are a lot of factors into play here so it’s more or less edjucated guesses. I’ll end up with two of these amp so if possible I could A/B different configurations. I will google the Odam caps, since I’ll never heard of them. Thanks for bringing them to my attention!
 
edjucated guesses
True, but you still should research mylar vs Teflon dielectric as it released to distortion before you decide. AN uses Mylar. V cap uses Teflon. Both of these are somewhat outliers. Most film capacitors use polypropylene, a very good material too. (there is another name for mylar, which is very similar to polypropylene, but they are NOT the same thing.)

Capacitor construction, and dielectric have the greatest effect on sound. In my humble opinion.
 
I believe Mylar equals polyester (NOT to be confused with polypropylene!) Google/DuckDuckGo is your friend. Look at the different dielectric material characteristics and then look what’s in the capacitor of your preference.

But your ear is the final arbiter. None of this accounts for construction quality or dielectric interface with silver versus copper versus aluminum. Many love both types of caps discussed.
 
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Thanks. I understand that V-caps are very popular. If I remember correctly Stereophile reviewed an 8900 with Audionote. Problem is that there are a lot of factors into play here so it’s more or less edjucated guesses. I’ll end up with two of these amp so if possible I could A/B different configurations. I will google the Odam caps, since I’ll never heard of them. Thanks for bringing them to my attention!
I use this Audio Capacitors document as a guide. The findings (Sound) are (to my ears) present a very good description to the applications of Crossovers and Amp usage.
https://www.humblehomemadehifi.com/Cap.html
 
I have finally assembled my 8900.

Some of the delay was due to my choice to paint the chassis. I have been learning how to do "automotive" painting. I sanded down the chassis down to the metal, filled in the seams/gaps with Bondo, resanded it, primed it with automotive primer, sanded that smooth, then applied 5 coats of single stage automotive paint (a very dark blue similar to Audi dark blue), then 3 coats of clear coat, then successive puffing with automotive compounds, etc until shining. It is far from perfect (no paint booth so plenty of dust landed on it while drying and I shouldn't have used single stage paint...). But this is part of the learning process.

The kit assembly went as smoothly as ELEKITS do, which is to say, smoothly. You can see from the images I used Audio Note resistors in most positions (and all of the signal path), otherwise takman and amtrans - all resistors were hand-matched between the channels. Lundahl OPTs, coupling caps are the ones VK recommended (VCAP CuTF) and lined the chassis with copper foil.

I have been listening to it with the 2A3 tubes and it has been driving the Reference 3A Nefes without any difficulty and sounds lovely. I then tried a pair of 300b's - this is where I am curious. The appropriate lights on the power board came on (see picture), but the LEDs around the volume pot are not both 'blue' as they should be. If you see in the picture, the LED on the right is blue/green and the one on the left is blue. When I plug in the 2A3s, both LEDs turn full green) but the right is still much brighter than the left.

So, is this a problem. Although, I believe the resistors in the LED path are 'identical' aka matched. Could it be an issue with the LEDs (or LED) itself?

Thanks
 

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