Aiqin/Oldchen Tube Amps

[mroboto]

You say the cathode is in the signal path, but in fact, the cathode is the place where there shouldn't be any signal.

My mods are very generic and this receipes are good for all my tube amps, DACs and solid state amps, soon I will probably recap a tuner, and I think about adding a lot of decoupling, Decoupling really change the caracter to in fact remove the caracter of the quite poor electrolytics capabilities at high frequencies compared to the bypass caps I use.

I did not go as further with solid state amps as decoupling all electrolytics in my tube amps, but did some.

 

[FlaCharlie]

You say the cathode is in the signal path, but in fact, the cathode is the place where there shouldn't be any signal.

The post I linked mentions primary and secondary audio paths and explains it better than I can. I fear we have derailed this thread so . . . I would suggest that you start a new thread entitled "Is the cathode resistor and bypass cap in the signal path?" Others here will explain it to you.

 

[nickytheshaf]

OK the the tung-sol's have arrived.
I must say they make a hell of a difference. the sound is no more fatiguing, it is quite detailled and not harsch anymore.
I must push the knob a little higher now but the sound is much more pleasant.
The psvane really don't do the amp justice.

 

[MWalt]

After reading this thread I thought it was time to get one of these puppies. Just got an Old Chen Luxury. Added a NOS GE 5U4G, two EL-34's from my Prima Luna Prologue Classic and a matched pair of Russian Reflektor 6N9P's. All new tubes (except the EL-34's). Out of the box sounds very good, even with new tube. etc. I started out with my Hornshoppe horns and a small sub. Sounded nice. Then I switched to a pair of resto modded Dynaco A-25's. A match made in heaven! Plenty loud too in my small listening room. I am very pleased with this amp and expect it will only get better once everything is fully broken in.

 

[mroboto]

I would be interested to see if someone with a frequency generator and an oscilloscope could show figures of 10Khz square waves before and after some mods similar as I explained, the difference of the ceramic caps etc...

 

[cdfac]

Just about to pull the trigger on the Nobsound/Aiqin version from Douk Audio. My introduction to Nobsound/Douk came from their little dual TPA3116 amp, which is really pretty remarkable for $45. I noticed that on eBay it's like $80 cheaper than on Amazon -- that's a pretty huge difference from the same seller. Already have some upgraded tubes lined up, just waiting a few more days to order the amp so that I can make sure I'm back from a work trip when it's delivered (need to sneak this one by the wife!). I think I will be building another set of high-efficiency DIYSoundGroup speakers to use with it.

 

[The Fuxtor]

Wow, long thread! Anyways, i just picked up one of these laochen el34b models. Sounds pretty good aside from some hum at higher volume. Just curious about a concensus of the chinese 5u4g rectifiers? Reading back a bunch of pages there was mention of changing out the first cap after the rectifier to 4.7uf? That or use an american brand tube? This the thing to do still? Also i noticed this unit is using kt88 tubes, thats fine for these guys? Anyone figure out how to kill some of the hum?
Thanks in advance!
Edit: I just looked and the tubes are actually EL34b.... The boxes the guy gave me say kt-88...

 

[Thefamous]

Wow, long thread! Anyways, i just picked up one of these laochen el34b models. Sounds pretty good aside from some hum at higher volume. Just curious about a concensus of the chinese 5u4g rectifiers? Reading back a bunch of pages there was mention of changing out the first cap after the rectifier to 4.7uf? That or use an american brand tube? This the thing to do still? Also i noticed this unit is using kt88 tubes, thats fine for these guys? Anyone figure out how to kill some of the hum?
Thanks in advance!
Edit: I just looked and the tubes are actually EL34b.... The boxes the guy gave me say kt-88...

The older rectifier tube wasn't a 5U4G. It was something else. I think they changed it because of the problems noted earlier in this thread. The cap on mine was correct (or close I think?) for that tube, although I can't remember what the value was off the top of my head. I did end up changing out a few components, but for the most part I was pretty darn satisfied. Have it playing in the kitchen/dining area for cooking and entertaining.

 

[The Fuxtor]

Does anyone know if the outputs are compatible with any other tubes?? KT-88? 77's??

 

[The Fuxtor]

Just sharing.

View attachment 1027142
Triode Mode looks like above, theres a jumper connecting both the pin together.

And there's the Yellow wire is hidden away below the board usually. You connect it when you want to switch it to Ultra Linear and remove the jumper wire. Refer below for UL setting.


View attachment 1027143

Thanks for the pics! So what seems to sound better? UL provides more wpc I believe?

 

[nickytheshaf]

Don't go with UL. I removed the tap this we and passed to triod with a 450ohm resistor betwen the pins. THe sound is much more calm, less fatiguing.
UL is too high and not that pleasant. Triod is more warm.

 

[nickytheshaf]

the opt's are not powerful enaught for KT88, only EL34 and 6CA7

 

[The Fuxtor]

Don't go with UL. I removed the tap this we and passed to triod with a 450ohm resistor betwen the pins. THe sound is much more calm, less fatiguing.
UL is too high and not that pleasant. Triod is more warm.

Would I just remove the yellow wire on the left leg of that 120 ohm resistor? I think it's on pin4

 

[nickytheshaf]

yes, removed and isolated.
I think the rsistor is 2kohm, I changed it for a smaller 450ohm. if it is 120ohm, my bad, I read it wrong , guess it's going back.
You have to leave a resistor between pins 3 and 4
the hardest part is getting everything clean with all this white silicone

 

[The Fuxtor]

yes, removed and isolated.
I think the rsistor is 2kohm, I changed it for a smaller 450ohm. if it is 120ohm, my bad, I read it wrong , guess it's going back.
You have to leave a resistor between pins 3 and 4
the hardest part is getting everything clean with all this white silicone

Awesome! Thanks

 

[Toober]

Hello, I'm new to this group. I bought one of these amps about a week ago. Had a few issues. First was a bad volume pot, next right channel kept cutting out, missed solder joint on the power tap to 6sl7, and the bias resistors burned up. They are 2 470 ohm resistors 2 watt. I replaced them with a Dale 10 watt 500ohm, and finally the factory tapped the right side B+ to the 6sl7 power feed. About 40 volts less going to the right channel.
Also, on mine there are 0.1uf coupling caps on the 6sl7 that don't appear in any pictures posted on line.
I upgraded the coupling caps to mundorf Evos, .68 uf and .2uf on the 6sl7. And put in a solid state rectifier (the type that goes into the tube socket) . Mullard new el34, RCA 6sl7 smoked glass.
It sound great now, power transformer runs at 108 degrees after 2 hours driving ADS L630 speakers (94db efficiency).
Even with the few issues it is a great sounding amp, well worth the money and time.
You can see in the picture the cooked resistors and the coupling caps on the 6sl7.

 

[The Fuxtor]

I would have returned it??

 

[Toober]

Well, I had planned on doing all of the upgrades anyway plus I got it new in box for 150.00 and it was his last one. My guess was it was a returned unit. Not a big deal, I love tinkering and modding.

 

[cdfac]

I would have returned it??

Makes me feel better about going with a Dennis Had amp, TBH.....Even if it's most likely to be fine.

 

[Stonegarden]

Anyone checked the fuse inside those amps? Mine had a 2 amperes fast fuse. I replaced it for 0.80 amper slow fuse. I could have used even a lower one I think...
I think it's very risky to run one of these amplifiers with a very high amperes fuse, in case of any problem, you could burn the whole thing up...