Nobsound EL34 Single-ended Class A tube amplifier

[ejman]

Hey folks (Frank and everyone)!

Well, it's been some time since I last gave a report about my Nobsound NS-13D amp. I bought it over a year and a half ago. I had a question about it, but need to explain what's happened with this amp. The last post, I reported I liked the amp but didn't care for the speaker hummmmm, regardless of which input was used (computer/turntable). Well, things got interesting in a very bad way.

The hum increased gradually to become so violent, it shook the upper part of the cabinet, where the transformers are housed. I opened the chassis and found the two smaller transformers were shaking like an SOB! The vibration was so pronounced, you could hear it in the other room. I took the top part of the case off and installed seven layers of electric tape and then remounted the top of the chassis on the bed of electric tape. This quieted the chassis down quite a bit, but you could still hear a loud hum from the amp PLUS the usual hum from the speakers.

Shortly after, the entire amp died. :-(

I looked everywhere and didn't see a fuse. Since I need it for work, I replace it with a new one from Amazon. Got it two days ago. I plugged all my OLD tubes in and fired it up. Immediately, the old stock rectifier tube flashed and the new amp went dead. <sigh> The rectifier tube blew, and now I had TWO dead amps! :-( I opened the chassis of my OLD dead amp, plugged it in, and decided to trace back where the voltage was dying out. This is where I feel VERY stupid! (I'm not a technician... I'm a hobbyist!) I noticed no power was coming off the back of the plug--I mean, nothing. The red "hot" lead read 0V. The plug had 120V coming off it. WTF! After close inspection, I noticed there was a fuse inside the plug housing. OMG! I didn't notice that. But it had a spare. Awesome! I changed the fuse.

Since the new amp came with tubes, I now used the new rectifier tube with all the old tubes. I plugged them into the old amp, crossed my fingers, cringed, and flipped the power switch. The tubes lit! A minute or so later, the old amp was playing! I didn't play it for long, so I don't know yet if it's actually fixed. The transformer hum normally took five or ten minutes to begin buzzing. I have no other spare rectifier tube (I ordered two new ones). So I don't want to run this old amp until I have a spare (I have three sets of all the other tubes). I'm only running the new amp now.

So after telling this looooong story, my question relates to the rectifier tube. I'm beginning to wonder if that was faulty from day one and contributing to the old amp's hum (both in the speaker and, later, the transformers and chassis). The old amp, I thought the transformers were faulty. Maybe it was all the rectifier tube? Can a bad rectifier tube cause AC hum through the speakers or buzzing/shaking transformers? Anyone have any thoughts on this?

Now that both amps are running, comparing the two, I think the new amp is what the old amp should have been. The old amp was always a little left-channel dominant with a mild hum and thin soundstage. This new amp has a balanced output with both channels presenting equally. Also, there's a much cleaner soundstage that's louder, richer, and deeper. You can hear the audible placement of instruments. The old amp sounded like you were listening to two speakers with a little bit going on in between them. The new amp, when I turn it full volume with no source playing, it's so quiet. I can hear only a little hiss at full volume. The old amp was a mashup of hiss and hum.

I appreciate any comments...

Wow, it sure sounds like you had some problems with your original amp. Just curious did you ever contact the seller? these are supposed to have a one year warranty although not sure what that covers if anything. Also I read that the original Chinese rectifier tubes on these amps are fragile and/or the design implementation is faulty so that a higher value capacitor is used that overdrives the tube. The recommendation I read was to use an older american 5U4GB tube as even the old ones on the auction site are supposed to last a long time and match with the capacitor value that overdrives the Chinese tube.

 

[Frank Sol]

I've been using a Tung-Sol 5AR4 almost from the beginning (3 yrs) with no problems - YMMV

 

[premington]

Wow, it sure sounds like you had some problems with your original amp. Just curious did you ever contact the seller? these are supposed to have a one year warranty although not sure what that covers if anything. Also I read that the original Chinese rectifier tubes on these amps are fragile and/or the design implementation is faulty so that a higher value capacitor is used that overdrives the tube. The recommendation I read was to use an older american 5U4GB tube as even the old ones on the auction site are supposed to last a long time and match with the capacitor value that overdrives the Chinese tube.

Thanks for the reply!

Actually, I believe the rectified tube is a Russian tube. The number on the tube is "5U4C". But the "U" is actually the 23rd character of the Russian alphabet--it has a pigtail on the lower right of the U. Researching it, I located one vendor selling these tubes, and they identify it as a Russian tube. Their picture is a 100% match to the stock tube that came with the amp. So I bought two.

What I'll do, when they arrive, is plug in my spare tubes with the new rectifier tube into the old amp and see if the transformers start buzzing and if there's an AC hum through the speakers. If the hum is gone and the transformers remain stable, then I have my answer, and my answer is good info for anyone reading this thread who has this amp. The rectifier tube, when it fails, can cause audible hum in the speakers and buzzing in the transformers.

But I don't know that for a fact, just yet. I'll report back what I find.

And, no, I didn't contact the seller. To be honest, I didn't know where the humming was coming from. I thought it was a bad ground someplace. I tried connecting an upgraded ground, but nothing worked. Now I know why... I don't have any grounding problem. This new amp sounds damn quiet! There's not even a hint of humming. Other than SET-related Class A amp hiss, she's as quiet as can be!

Also, I bought this on Amazon... I didn't realize, until now, that I think Dauk Audio (?) is the vendor these amps come from. It's been close to two years since I bought it, so I don't remember the details, and it doesn't matter because the warranty is expired. Now... The new amp, I bought a four-year extended warranty, just in case. I don't usually buy those things, and I'm skeptical it would be honored (hopefully I'm wrong). But after what I've been through, it's cheap, added protection in case of failure.

So... It's distinctly possible, when I get the new rectifier tube, that I may find the old amp works perfectly. Then I'll have TWO of these amps kicking around my home. What do I do with the spare??? LOL!

To be honest, I really do like this amp. It's great. And it sounds excellent, given its price. I think I'm just living in the land of tubed equipment, and not being a technician who has the knowledge and equipment to throw this baby on a spec an and scope to really see what's going on inside, I have no way of properly diagnosing problems. I'm happy with the new amp, and fine with knowing I have a spare. I just don't know what to do with it.

 

[Nixxuz]

Thanks for the reply!

Actually, I believe the rectified tube is a Russian tube. The number on the tube is "5U4C". But the "U" is actually the 23rd character of the Russian alphabet--it has a pigtail on the lower right of the U. Researching it, I located one vendor selling these tubes, and they identify it as a Russian tube. Their picture is a 100% match to the stock tube that came with the amp. So I bought two.

What I'll do, when they arrive, is plug in my spare tubes with the new rectifier tube into the old amp and see if the transformers start buzzing and if there's an AC hum through the speakers. If the hum is gone and the transformers remain stable, then I have my answer, and my answer is good info for anyone reading this thread who has this amp. The rectifier tube, when it fails, can cause audible hum in the speakers and buzzing in the transformers.

But I don't know that for a fact, just yet. I'll report back what I find.

And, no, I didn't contact the seller. To be honest, I didn't know where the humming was coming from. I thought it was a bad ground someplace. I tried connecting an upgraded ground, but nothing worked. Now I know why... I don't have any grounding problem. This new amp sounds damn quiet! There's not even a hint of humming. Other than SET-related Class A amp hiss, she's as quiet as can be!

Also, I bought this on Amazon... I didn't realize, until now, that I think Dauk Audio (?) is the vendor these amps come from. It's been close to two years since I bought it, so I don't remember the details, and it doesn't matter because the warranty is expired. Now... The new amp, I bought a four-year extended warranty, just in case. I don't usually buy those things, and I'm skeptical it would be honored (hopefully I'm wrong). But after what I've been through, it's cheap, added protection in case of failure.

So... It's distinctly possible, when I get the new rectifier tube, that I may find the old amp works perfectly. Then I'll have TWO of these amps kicking around my home. What do I do with the spare??? LOL!

To be honest, I really do like this amp. It's great. And it sounds excellent, given its price. I think I'm just living in the land of tubed equipment, and not being a technician who has the knowledge and equipment to throw this baby on a spec an and scope to really see what's going on inside, I have no way of properly diagnosing problems. I'm happy with the new amp, and fine with knowing I have a spare. I just don't know what to do with it.

Put the old one on BT. And I can't say for sure about the extended warranty, but Amazon has about the best CS in the industry.

 

[premington]

Put the old one on BT. And I can't say for sure about the extended warranty, but Amazon has about the best CS in the industry.

What is BT? I was thinking about eBay, but I haven't decided if I want to part with it. It's a backup, in case I have problems.

Amazon sells these extended warranty packages through SquareTrade, which I think I read is owned by Allstate. I think the key is to read the fine print and understand the exclusion list, which a lot of people don't take the time to do. Hopefully I'll never need it. It was only $14, so I'm not worried about it. What's funny is, it's a 4-year extended warranty, but it doesn't cover the time it's on manufacturer's warranty. The two warranties overlap, so it's really a 3-year warranty, since the amp has a 1-year warranty. Weird.

 

[Nixxuz]

What is BT? I was thinking about eBay, but I haven't decided if I want to part with it. It's a backup, in case I have problems.

Amazon sells these extended warranty packages through SquareTrade, which I think I read is owned by Allstate. I think the key is to read the fine print and understand the exclusion list, which a lot of people don't take the time to do. Hopefully I'll never need it. It was only $14, so I'm not worried about it. What's funny is, it's a 4-year extended warranty, but it doesn't cover the time it's on manufacturer's warranty. The two warranties overlap, so it's really a 3-year warranty, since the amp has a 1-year warranty. Weird.

BT is Barter Town. It's part of the Audiokarma subscriber section. People buy and sell all things audio related, (and some not!).

 

[KlipschFan61]

fingers still crossed

The power tubes seem to have a longer lifespan than their driver tubes. I went through two sets of 6SN7 input tubes before I signed off on JJ.

 

[KlipschFan61]

Anyone have any experience with this model?

I have the classic version of the same amp. Can be a little temperamental but it sure sounds delicious with the right tubes in it.

 

[Frank Sol]

personally have put about 50-60 hrs on the new JJ E34L + the 24 hrs 'burn-in' at Tube Depot

so far so good... Nice sounding tubes

The power tubes seem to have a longer lifespan than their driver tubes. I went through two sets of 6SN7 input tubes before I signed off on JJ.

Unfortunately I believe its hit or miss with tubes - more hits hopefully

 

[Poultrygeist]

I'm running 12ax7 Telefunkens preamp tubes in use since the 1950's.

 

[MATT0404]

I've been running the Gemtune GS-01 for a few months with very good results. I've done a few small mods to improve the sound. I just replaced the stock 6H9C tubes with a matched pair of new Tung Sol 6SL7GT with good results. This got rid of a bit of a hiss/crackle through the speakers. Now my Chorus II's are nearly silent when using this amp. There's just the faintest hum through the woofers with my ear 8 inches from the speaker. Otherwise, it's inaudible.

I've also replaced the stock volume pot with an Alps Blue Velvet 100k. This was a good upgrade in terms of volume tracking and channel separation.

Next up, I've ordered a SED Winged C 5U3C rectifier tube. I should have it sometime next week. I'll keep you all posted. I'm also considering replacing the EL34's as I doubt the stock EL34's are authentic. They don't sound bad, though, just curious how a good pair of EL34's would sound.

So far, so good with this inexpensive amp. I bought this one open box from Amazon for something like $250 shipped. Hard to beat at that price and It sounds great through my Chorus II's!

 

[Frank Sol]

Chorus II are great speakers for that sort of amp

Dont sell the PSVANE EL34 short like I did at first... nice tubes

 

[MATT0404]

Chorus II are great speakers for that sort of amp

Dont sell the PSVANE EL34 short like I did at first... nice tubes

Lots of people say the Chorus II's really shine with a 200+ wpc amp, but mine sure do sing with any/all of my low powered tube gear.

I don't have anything bad to say about the current Psvane (assuming authenticity) tubes. They sound pretty good but lack dynamics compared to the EL84's in my Scott 222. I'm not sure if this is a fault of the tubes or an inherent characteristic of the amp itself. This makes me curious to try another pair of EL34's. That said, I really like the midrange/vocal presentation of the amp as-is. Voices are very forward and prominent in the soundstage, but have a nice mellow characteristic. Great for acoustic and jazz music.

 

[Poultrygeist]

Lots of people say the Chorus II's really shine with a 200+ wpc amp, but mine sure do sing with any/all of my low powered tube gear.

I don't have anything bad to say about the current Psvane (assuming authenticity) tubes. They sound pretty good but lack dynamics compared to the EL84's in my Scott 222. I'm not sure if this is a fault of the tubes or an inherent characteristic of the amp itself. This makes me curious to try another pair of EL34's. That said, I really like the midrange/vocal presentation of the amp as-is. Voices are very forward and prominent in the soundstage, but have a nice mellow characteristic. Great for acoustic and jazz music.

The Chorus II's are 101 dbs so you're reaching a good listening level with a fraction of that all important first watt and hearing everything it has to offer.

 

[KKnight]

I’m not 100% sure I understand what your comment means... but I’m Reasonably sure you owe me a $100 bucks.

I’ve had the the “bottom” cover off. It’s point to point wired. Everything including the sador is neat and tidy. You shouldn’t spout things you don’t know anything about. It will make you sound less creditable.

Have fun with the counterfeit electrolytics you obviously will not verify as being genuine and in spec.. Facts about this amp and all the other similar amps and the 50% counterfeit rate on the lytics already written in stone for at least the past 5 years. Plus the fact they are all tier 4. Dont have $100 do ya..

 

[Frank Sol]

KKnight , thank you for bringing some early Holiday Cheer to AK

 

[Funky54]

Have fun with the counterfeit electrolytics you obviously will not verify as being genuine and in spec.. Facts about this amp and all the other similar amps and the 50% counterfeit rate on the lytics already written in stone for at least the past 5 years. Plus the fact they are all tier 4. Dont have $100 do ya..

Are we talking about the amp at the beginning of the thread or the amp I posted. A picture of the inside was posted by another member. Mine is point to point. I’m at the point where I see nothing useful or educational will come from any of your posts. I can trim out uneducated ridiculous bloveating by using the ignore feature.

 

[Poultrygeist]

Have fun with the counterfeit electrolytics you obviously will not verify as being genuine and in spec.. Facts about this amp and all the other similar amps and the 50% counterfeit rate on the lytics already written in stone for at least the past 5 years. Plus the fact they are all tier 4. Dont have $100 do ya..

The main thing we should be concerned with is the sound. Obviously you haven't heard this amp.

 

[ejman]

Following KKnight advice I decided to purchase a GemTune BL-02 EL-34 tube amplifier to verify his claims and every thing he has said is absolutely true!. Fake point to point wiring (there is an invisible circuit board there if you hold the light just right) the stainless steel chassis is obviously fake ( I don't know why my magnet won't stick to it but it's probably a fake Chinese magnet as well). The tubes are obviously fakes as well and if you look real close there are fake lite solid state devices in them which are probably fake too. And the sound the horrible fake sound that I'm listening to as my Creek amp sits by unused Why? because I love the fake sound of the fake tubes that's why!

 

[Poultrygeist]

The Chinese Dared and all it's fake parts blew away my Fisher 500, ST70, and Scott with it's superior resolution.