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Nobsound EL34 Class A Single-ended Tube Amplifier Stereo HiFi Amp Kit?
Nobsound EL34 Class A Single-ended Tube Amplifier Stereo HiFi Amp Kit?
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Old 27th October 2017, 03:54 AM   #1
HarryY is offline HarryY  United States
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Default Nobsound EL34 Class A Single-ended Tube Amplifier Stereo HiFi Amp Kit?

The price is OK (about 300 dollars).

It looks like a nice kit to play with. I don't expect great performance but
It would be one I could experiment on if I wanted to.

I was curious if anyone had built one of these?
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Old 27th October 2017, 05:06 AM   #2
rongon is offline rongon  United States
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Nobsound EL34 Class A Single-ended Tube Amplifier Stereo HiFi Amp Kit?
I haven't built one, nor seen one. But these kits have been discussed a lot over the years.

Nobsound, Douk Audio, same thing.

EL34 Single-ended Class A tube amplifier KIT
Douk EL34 Amp kit
Tube amps on E-Bay
APPJ PA0901A anyone?

It looks like it's a cheap way to get the parts you need to get started, but you are likely to end up doing your own troubleshooting of problems (hum, unbalanced output left/right, possible mistakes on schematic, figuring out color coding of wires, etc.). Also, the transformers are likely to be cheap/low quality. Many argue that it's not a great first kit, because it won't go together without problems to be solved. Then again, solving those problems is probably a good way to learn.

Last edited by rongon; 27th October 2017 at 05:08 AM.
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Old 27th October 2017, 02:08 PM   #3
Demonkleaner is offline Demonkleaner  United States
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FWIW I recently built one mainly out of curiosity. It sounds decent to me. I had to upgrade the supplied volume pot and put some Russian coupling caps in it.

As stated above, there was a hum issue in the right channel. Tube layout places the RH input tube away from the volume pot requiring a sort of long cable to connect it. I managed to get it cleaned up. Hope this helps.
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Old 27th October 2017, 03:29 PM   #4
audiowize is offline audiowize  United States
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The specifications looks like very, very typical Chinese lies.

You might get 13W out of that amp, but it will be at 1kHz and very high THD (well over 20%).

The size of the transformers should give decent frequency response at 2-3W. Anything more than that and distortion/bandwidth will be a problem.

Several of the schematics linked show an ultralinear wired EL34 and no global feedback. This is going to cause a lot of problems.

I don't mean to be overly negative, but last week a friend of mine brought over a "well respected" built in China but designed/distributed in the US amplifier. The company said it would do 45W at 5% THD. We measured 3W at 5% THD and 40W at 15% THD. The bandwidth was also quite a bit poorer than specified. He was very frustrated!

If you buy one of these inexpensive Chinese kits, I would budget plan to spend at least an additional $200-300 to get some proper transformers. It can be very difficult to trust that the power transformer is wired for 120V and not 110V. (Some schematics are listing a 220V power transformer for international users, which usually means a 110V transformer will go to the US/Canada/Japan. It will overheat and fail.)
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Old 27th October 2017, 03:56 PM   #5
HarryY is offline HarryY  United States
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Quote:
Originally Posted by Demonkleaner View Post
FWIW I recently built one mainly out of curiosity. It sounds decent to me. I had to upgrade the supplied volume pot and put some Russian coupling caps in it.
As stated above, there was a hum issue in the right channel. Tube layout places the RH input tube away from the volume pot requiring a sort of long cable to connect it. I managed to get it cleaned up. Hope this helps.
Thank you

It would be more of a something to play with than anything else.
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Old 27th October 2017, 04:50 PM   #6
toobnick is offline toobnick
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hello poster, i have built a few china kits (3), a 6v6 preamp, which with my choice of film caps , brand and type and a fix to the power supply, as is necessary on any china kit, as their power its 220 so they make a two coil primary power trans , in parallel 110, in series 220. other than a 330uf cap right off the tube rec,of their original design(should be about 33-20uf) this preamp sounds outstanding , also with my choice of tubes.

its pre pre stage is a pentode 6au6 and input pentodes imho sound great. i also have built the kit you are talking about, the el34 kit, the output transformers aren't bad they sound pretty good, they aren't Sophias' or tangos' or anything like that but entry-level the wiring diagram is pretty crazy, non symmetrical channels, they used both sides of the 6sl7 parralled to each other, which just isnt how its done, and as mentioned the volume pot is one on side of the amp, so rule of thumb always use the same length wire in a project for each channel, yes one maybe two inches too long for a seemingly close contact point, but loop it neatly, do not coil it , if you want a balanced amp this is necessary.

and for the input research 6sl7 SRPP wiring method to usefully use both sections of the tube.(or i guess use just one side as that is plenty to properly drive the output tubes) and for the 110 power transformer, the make these little black disks with leads called cl80, cl90 or lower, but those two are the most useful to use in series with your ac input wiring.put em inbeween your switch and hot lead of PT, so for your kit attach them to the output of the power switch, up front, and a piece of wire, or the hot lead from the PT itself to make the connection. the components are current inrush limiters and cold they are a higher resistance , hot the are less resistant , but ive found using them on vintage hear helps with the 115, 117 voltage rating of power trans. so if you find cl80 use two in series with your kit. not only when your transformer rated at 110 , here supplied with 120-125, get hot and eventually fail, but the voltages it ***** out is much higher too, so your heaters run way high, your B+ voltages run wildly high for the bias point of supplies provided with the kit.

this kit built out of the box without these cl80s won't operate correctly, the shugong(spelling?) tubes provided are ironically robust, but if you wanna use rft, mullard, tesla or any other super expensive el34 they sound ok for about 5 minutes then the high heaters and high b+ voltage deteriorates the sound to an unlistenable state, if left to play this way id assume the tubes would self destruct or something lol. oh and i like the floating ground technique, and if you do go srpp input, elevation of those heaters is required. if you're interested ill explain Nick
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Old 27th October 2017, 08:50 PM   #7
pcan is offline pcan  Italy
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Nobsound EL34 Class A Single-ended Tube Amplifier Stereo HiFi Amp Kit?
You may find this amplifier kit at a significant discount over the regular price if you look around and keep checking. I got a full 25% discount for mine, including sales tax and shipping. This offer is expired now, but every once and a while I see it again from different sellers. Maybe you may contact the seller and ask for it.

Actually, I believe that there are two sister kits: one with the 5 tubes on the same line and the metal chassis that extends to the sides (they may be covered by a piece of fake wood), and another one with staggered tubes and wooden side panels. Careful inspection of the schematics and the parts I see on the pictures, they looks to be otherwise identical. I bought the all-metal chassis with 5 inline tubes. The output transformers are a bit small but not too bad. Power transformer is put to its absolute limits by the EL34 filaments. It works cooler with smaller tubes. The filter choke could have a higher inductance, but is better than nothing.

On my latest rewire, i replaced the 6SL7 with a 6SH7 wired as pentode. I also tried a 6SN7 with the two sections connected as simple voltage amplifier, one one after another. There is a lot of place inside the chassis to play with. The tubes that came with my amp aren't of the worst quality, surprisingly. No loose debris inside or mishaped metal. Electrically, they are far from matched, but sound is better than the half-dead vintage tubes I used before to put on my test amps. At the list price, this kit is still maybe a bit pricey for what it offers; it becomes a good value with some discount. Be sure to check import and shipping cost, they may be significant (on my case, they add about 33% to the price).
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Old 27th October 2017, 09:33 PM   #8
audiowize is offline audiowize  United States
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How about instead of buying a piece of junk, you just buy parts and a piece of aluminum?

Two Edcor XSE15-2.5K are $22.52 each
One Edcor XPWR-066 is $69.44
Two EL34s are about $25
One 6SL7 is $10

You'll need about another $100 to get yourself a piece of aluminum, some sockets, hardware, terminal strips, resistors, and capacitors.

If you don't own a drill press or a hand drill, you'll need to snag one (I recommend looking locally for something used), and a few drill bits (you'll want the conical shaped drill bit that does multiple large holes).

You'll need a $10 chunk of wood and some wood glue from the HW store to make a base to stick this in.

If you have some tools laying around (or a friend close by with some tools), we are talking about less than $300 here...

If you need to buy some tools, you'll be spending a little more than the Chinese kit, but you'll get a 120V power transformer and budget output transformers that are quite decent.

Heck, if you aren't having to chase down tools (too bad you aren't in Seattle), you could really break the bank and use the GXSE 15W transformers that are $41.70 each and you're still miles ahead.

Last edited by audiowize; 27th October 2017 at 09:52 PM.
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Old 28th October 2017, 01:11 AM   #9
HarryY is offline HarryY  United States
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Quote:
Originally Posted by pcan View Post
--- snip --- Power transformer is put to its absolute limits by the EL34 filaments. It works cooler with smaller tubes.
---Snip ---
I was wondering about that part as I have an Elekit TU-8200 and it runs nice with 6L6 tubes but gets pretty warm with higher current filaments.
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Old 28th October 2017, 01:12 AM   #10
HarryY is offline HarryY  United States
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Quote:
Originally Posted by audiowize View Post
How about instead of buying a piece of junk, you just buy parts and a piece of aluminum?
--- snip --
That may be an option, as this is just kicking tires
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