Aiqin/Oldchen Tube Amps


It's a little hard to tell what's going on there with all the white goop covering the connections. Not sure why they would do that.

It doesn't look like it's UL. If it was there would be two wires coming from the output transformer to the tube. One to pin 3 (plate) and a separate one to pin 4, which is the screen (G2). UL operation requires a transformer which is built for UL operation and has this special winding.

Technically, the tube itself (EL34) is not a true triode but it can be "triode strapped". If it were wired in triode, pin 3 (plate) would be connected to pin 4 but this is supposed to be done with a 100 ohm resistor, not a direct connection. The goop makes it difficult to tell but they may have just connected the two directly. If so, I'm not sure how much of a problem the missing resistor might be. I think the idea is to keep the screen voltage lower than the plate voltage.
 
I think it would be better to run cables from the amp to the sub line-level inputs then from the sub line-level outputs to the speakers. I think it is basically the difference between running them in parallel vs. series. But since the sub has little/no load, I forget how to do the electrical calculations. Can someone remind me?
This is probably late, but I did things a different way.
I'm running 2 Dayton Audio SUB-1500's in my system. My towers have the binding posts to be bi-amp capable. What I did was run a set of wires from the 2nd set of binding posts on each tower to the subs line level ins. The double posts are, of course, sharing a bridge. This way I could get separate low frequencies to each sub from each channel. It may not be totally needed, but it makes me happy when I hear a bass line from my right or left and it's localized to that sub.
 
I've had a "luxury bluetooth" el34 for about 6 months. about a month ago the tubes started making a bit of hum and ticking noises, especially at start up. As of yesterday, it won't turn on at all. I suspect a tube or tubes have burnt out. But I'm pretty ignorant on these things. Should I attempt to swap one or more of them out? Is there a repair place in Los Angeles any of you can recommend to either buy tubes and/or have it serviced? Thanks in advance.
 
I've had a "luxury bluetooth" el34 for about 6 months. about a month ago the tubes started making a bit of hum and ticking noises, especially at start up. As of yesterday, it won't turn on at all. I suspect a tube or tubes have burnt out. But I'm pretty ignorant on these things. Should I attempt to swap one or more of them out? Is there a repair place in Los Angeles any of you can recommend to either buy tubes and/or have it serviced? Thanks in advance.

I would start with the rectifier tube and power supply first.
 
ith the rectifier tube and power supply fir

Thank you for your reply.

I'm looking at the following tube upgrades...

couple of NOS Melz 6H9C tubes off ebay
couple of Tung Sol EL34b and a "preferred" 5U4G from the tube store

Where can I find the power supply?
 

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As of yesterday, it won't turn on at all.

"Upgrading" the tubes, especially with overpriced stuff off ebay or from "boutique" sellers, will not solve your problem. That said, if you check with some of the major tube dealers you'll find quality NOS American 6SL7s for $10 to $20 each. NOS American 5U4s are $15. Strong testing used tubes can be found for even less.

Do you mean you aren't getting any power to the amp at all? Is the fuse blown? Or do you mean that you aren't getting any sound but at least some of the tube heaters are lighting up? You need to troubleshoot the problem first.
 
No power whatsoever. The switch doesn't light up...nothing. I'll check the fuse when I get home. I can't believe I didn't do that first. :/
 
Btw, I would strongly suggest having someone else do the troubleshooting if you do not have experience working on tube amps as the high voltages inside can kill.
 
A fellow member earlier said that the rectifier tube went bad and the amp started blowing fuses. So perhaps you're experiencing the same. Good luck fiiguring it out!
 
Six months and down.

Long enough to sell it and that's it. Hardly fit for purpose. Lucky it didn't catch on fire.

If you want to keep it get a tech to check and fix it properly. Forget tube upgrades for now. It's busted.
 
No power whatsoever. The switch doesn't light up...nothing. I'll check the fuse when I get home. I can't believe I didn't do that first. :/

I take it the fuse was OK? If so and the tube heaters are not lighting up it would seem that either no power is getting to the power transformer or that the transformer is damaged, although that should have blown the fuse, in theory.

I live in Los Angeles. There’s gotta be a good amp repair place here. Suggestions?

I'm not sure how much techs in LA charge. Given the cost of living in California I'm guessing the hourly rate is pretty high. How much do these amps cost? The cost to repair might approach the original purchase price if it's something serious.
 
But it might also be something simple. One of my tube amps failed to start and it was just the power switch that needed replacing. Cost me nothing (mfr supplied a free replacement). Best of luck to Seth. Definitely test for residual power after unplugging and before touching anything inside the set.
 
Yeah, when I said that one possibility is that no power is getting to the power transformer, I should have been more specific. That would indicate a bad switch. Just bypass the switch and see what happens. If you're lucky, that's all it is. Go out and buy a Lotto ticket.

If there is still no power, and the tube heaters aren't lighting up (I assume they are AC heated), then the transformer primary is likely toast. If the heaters light but there is no sound, there are several possibilities. One of the resistors in the power supply may have burned up because too much current was being drawn. This should be obvious if you look inside. If so, you need to figure out why before replacing it. Perhaps the rectifier tube died. Replace it and see if all is well.

Judging by the comments of owners, the tubes that ship with these Chinese amps are often poor quality. And, as I've mentioned earlier in this thread, there are numerous stories about power transformers whose ability to deliver the current needed by the amp is marginal. Also, they often use power supply capacitors which, according to the tube data sheets, are much too large and put unnecessary stress on the rectifiers. This can lead to arcing (maybe that's what you heard?) and to power transformer failure.

The reliability of the ChiFi amps seems to be hit and miss. This is why I always suggest refurbished vintage gear. Plus, vintage gear has a track record of appreciating in value.
 
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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?
 
Based on your and another's experience, I'd replace the rectifier tube, then put in a new fuse and see if that takes care of it.

On that topic, what do others recommend for an inexpensive replacement of the rectifier tube?

My specs say my rectifier is a 5Z3P, is that the same as a 5U4G?
 
I've got a Gemtune GS-02 that behaves in a similar manner. If you need a source for 5U4G rectifiers that don't blow, try these:
https://nesstone.com/product/sed-5u4gb-winged-c-premium-rectifier-tube/

I also found that 6SN7's driver tubes don't work well either. Stick with the stock ones or find some Shuguang 6N8P's for spares.

The power tubes can be swapped with minimal impact but I've found through experience (and 4 blown fuses and 4 rectifiers) that this was the only recipe that keeps it happy.
 
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The EH rectifier worked well but went nuclear on me during one of my amp's 'tantrums'. The fuse in my amp is a 3A 250V buss. I invested in a few extras as one might imagine.

The Winged C is a nice tube for the price. I think the EH was about the same price. The stock rectifier had a loose base and started arcing after about a month. I'm not using that one anymore.

I just don't plan to mess with the 6N8P tubes anymore. Swapping to 6SN7's never went well for me.
 
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