Aiqin/Oldchen Tube Amps

[FlaCharlie]

Update. The fuse was blown. I replaced it. I turned the switch and the single 5U4G tube popped and flashed for a split second and it had blown another fuse. Something shorting inside or maybe just a new 5U4G and fuse?

What brand of 5U4 do you have in the amp now and where was it made?

I'm always a bit skeptical when it comes to new production tubes. Maybe that's unfounded in some cases but there are known issues with some new production rectifiers, although I haven't heard anything about the new 5U4s. Just because it's labelled 5U4 doesn't mean it actually meets the specs of the original 5U4.

I'd suggest buying a NOS (new old stock) American 5U4GB from one of the major tube dealers (who stock millions of tubes) or find a strong testing used one on eBay. The major dealers sell them for $15.

These guys are just up the road from me: http://www.vacuumtubes.net/prices.htm

These guys are down in Orlando: http://www.esrcvacuumtubes.com

Have you looked inside the amp for any obvious issues like evidence of overheating? If not, do so but remember that PS caps can remain charged long after the amp has been turned off and unplugged.

Also, what is the value of the first PS cap - the first capacitor that's connected to the rectifier? As I mentioned these amps frequently have oversized caps which can result in rectifier arcing. Some of the ChiFi amps shipped with rectifiers whose data sheets specify a maximum first cap of 4uf yet the amp uses 47uf or more. That's a recipe for disaster and illustrates the poor engineering that some of these amps have become known for.

See my earlier posts in this thread, starting on page 5.

A real, American, 5U4GB allows the use of a 40uf cap according to the data sheet. Even if this is a SE amp that draws less current, I would not go higher than 47uf, which is a standard value. Voltage rating should be 450v unless the original is rated at a higher voltage, which I doubt. But, if so, don't go lower.

Also, the use of a 3A fuse in an amp like this, which can't be drawing that much current, seems like a decision that was made to limit customer complaints, not to protect the amp. I would expect a lower amp fuse. If it's a fast blow fuse, I'd be tempted the try a Slo-Blo fuse rated at 2 or 2.5A. Whatever you do, don't go higher than the stock value.

 

[warmseth]

Are these the appropriate fuses? The GMA type?

https://www.homedepot.com/p/Cooper-...r-Electronic-Fuses-2-Pack-BP-GMA-3A/100192626

 

[GChief]

Always, always, always put a meter to a fuse before you install it!!

 

[warmseth]

Flacharlie the tube is Chinese...

 

[warmseth]

Chief can you recommend a meter to buy?

 

[GChief]

For what you need any “cheap” one at a big box store. It sux putting a bad new fuse in then chasing your tail. I have a $10 Craftsman for the House.

 

[warmseth]

All the tubes except for the one in question are pretty solid. This one is not. Bad cap?

 

[FlaCharlie]

View attachment 1267871 Flacharlie the tube is Chinese...

That's what I expected. Is that the rectifier tube that came with the amp? If so, order an American 5U4GB. They are plentiful and cheap - $15 from the major dealers I linked earlier. Don't try to save a few dollars by buying a new production Russian or Chinese tube.

If you can post a pic of the inside of the amp, and especially the power supply caps, it might be helpful. The positive of the first cap will be connected to either pin 2 or pin 8 of the rectifier. There might be some obvious signs of a problem and we can see what the value of the first cap after the rectifier is so we know it's not too large. That's usually the only way to know since they don't usually supply schematics for these amps.

As I posted much earlier in this thread . . . the Chinese 5Z3P rectifier is rated for a 4uf maximum value for the input capacitor and it's likely that they use a 47uf cap. It is not the equivalent of a 5U4GB but since it's also a 5v tube and it draws the same heater current and has the same pinout you can safely replace it with a 5U4GB. And, in this SE amp, 47uf will be fine with a real, American, 5U4GB.

All the tubes except for the one in question are pretty solid. This one is not. Bad cap?

While that is pretty loose in its socket, you can't tell anything about a tube's health like that. The problem is almost certainly due to poor design - using a rectifier whose data sheet specifies a maximum 4uf input cap with a 47uf (or maybe even larger??) cap. Get a proper American 5U4GB and, if it's loose in the socket you can, after draining the voltage from the caps, tighten up the connectors in the socket.

 

[warmseth]

Is that the rectifier tube that came with the amp?

It is. That’s the tube that came with the “deluxe” package. I feel like I should order a couple good tubes and drop this with a pro to go through to make sure it all looks good

 

[FlaCharlie]

It is. That’s the tube that came with the “deluxe” package. I feel like I should order a couple good tubes and drop this with a pro to go through to make sure it all looks good

I'd hold off for now on taking it to a tech. Order the tube and, while you're waiting for it to arrive, post some pics of the inside here. There is a good possibility that the issue was entirely caused by the mismatch between the stock rectifier tube and the use of a too large input cap. Hopefully the fuse blew before any damage could be done to the transformer. If so, after replacing the tube it will work fine again. If there is still a problem, THEN find a tech. No need to spend more $$ than is necessary.

 

[ProblemChild]

I am a new member and this is my first time on this forum. Would you have a schematic for a Oldchen or Aiqin tube amplifiers standard model, may also be a Gem-Tune BL-02 . I have looked everywhere I could think off. I would appreciate all the help you could give.
Thank you for your time.
ProblemChild.

 

[zepagas]

Hi, Morton

That's a bonus possibly if the reliability issues of the Chinese and Russian rectifiers are correct.

I'd be replacing the 100uf/450v cap with a 42uf/450v Panasonic or other quality cap, preferably from a reliable source. Something around 40uf anyway, and no lower in voltage.

That's about the limit of what I can advise to someone.

Ηι.Ι need 2 such capacitors? Where are placed inside the amplifier?Thanks

 

[FlaCharlie]

Ηι.Ι need 2 such capacitors? Where are placed inside the amplifier?Thanks

I strongly suggest that you read through this entire thread.

The cap that is sometimes much higher value than it should be is the first cap after the rectifier tube. The correct value of the replacement depends on the type of rectifier that came with the amp. If your amp came with a 5Z3P, you should replace it with an American 5U4GB and the first cap should not be more than 47uf. If your amp came with a 5Z4P, you should replace it with an American 5Y3GT and the first cap should not be more than 22uf. Voltage ratings should be 450v unless the original cap was higher voltage, which I doubt was the case.

If you keep the original rectifier tubes, the largest value you should use for the first cap is 4.7uf.

 

[FlaCharlie]

I am a new member and this is my first time on this forum. Would you have a schematic for a Oldchen or Aiqin tube amplifiers standard model, may also be a Gem-Tune BL-02 . I have looked everywhere I could think off. I would appreciate all the help you could give.

I don't own one of these but my impression is that there are often significant differences between the various brands even though they are probably made in the same factory. Here's one I found somewhere. The person who posted it notes the differences between his amp and the schematic he found. Your's might be completely different than either. If you want a truly accurate schematic of your amp you'll probably just need to draw one yourself.

yourself.

 

[thinice]

Looking for some advice here. I have an oldchen, similar to some in the pictures here. A few months ago the power switch "exploded" (not electrical, the plastic just broke and the whole thing came apart". After a few months I got the wrong switch from the manufacturer, then the right one a few months after that. Soldered it in and...nothing. Testing resistance across the switch, it looks like the solder is okay (I'm not an expert solderer to say the least) and the switch seems to work, but the amp just won't turn on. I put the tubes in, plug in the speakers, hook it all up and...nothing. I haven't wanted to test the thing plugged in as I'm a bit of a neophyte. Any tips or thoughts? I will check the fuse, but I have tested resistance from the socket to the switch and it seems to have a continuous run, so I assume the switch is good...

 

[ShaneC]

So those of you that have had one of these for a while, would you still recommend them?

Looking to make my first journey into tubes.

 

[thinice]

So those of you that have had one of these for a while, would you still recommend them?

Looking to make my first journey into tubes.

It's my only point of reference, but I'm very happy with it. Only thing I'd note is that it sounds best turned up. I don't know how to describe it the best, but as you turn it up it adds volume, but less than you'd expect, but what it does add is more detail to the music (for lack of a better word, I'm not great at describing sounds). I wish that I had got it with a headphone jack so I could listen to it loud when the little ones are sleeping, but other than that very happy with it.

 

[thinice]

Looking for some advice here. I have an oldchen, similar to some in the pictures here. A few months ago the power switch "exploded" (not electrical, the plastic just broke and the whole thing came apart". After a few months I got the wrong switch from the manufacturer, then the right one a few months after that. Soldered it in and...nothing. Testing resistance across the switch, it looks like the solder is okay (I'm not an expert solderer to say the least) and the switch seems to work, but the amp just won't turn on. I put the tubes in, plug in the speakers, hook it all up and...nothing. I haven't wanted to test the thing plugged in as I'm a bit of a neophyte. Any tips or thoughts? I will check the fuse, but I have tested resistance from the socket to the switch and it seems to have a continuous run, so I assume the switch is good...

Self-reply for anyone reading this thread. Turns out the version of this amp that I have has a fuse incorporated into where the power cord plugs in. They also (luckily) have a spare packed in there too. My fuse had simply blown. I replaced it after putting in the new switch and all was well.

 

[ejman]

So those of you that have had one of these for a while, would you still recommend them?

Looking to make my first journey into tubes.

I've been listening to my new Gemtune BL-02 amp for about three months now and so far its been great. The single ended class A sound is really growing on me even though I'm using less than ideal speakers @ my office setup ( Paradigm Atoms) which at 89 db efficiency are about 10 db too low from what I read. On the other hand the speakers are about 2 -3 ft from my ears (Desktop setup) so I'm sure that helps. Its weird but I find I'm enjoying this sound to such an extent that I'm listening a lot less to my main system ( Magneplanar speakers, Conrad Johnson /Jolida amps, Maple Tree preamp) Go figure - cheap Chinese tube amp + 2 inexpensive mini speakers augh!!!

 

[FatDonny]

So those of you that have had one of these for a while, would you still recommend them?

Looking to make my first journey into tubes.

I have no regrets getting mine. I think some tube rolling will get mine dialed in to my ear. I have not had any problems with the original build. Still sounds great!