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Old 20th September 2011, 08:17 AM   #1
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Default Chinese tube amp mods?

Hey all,
After checking out some HiFi tube amps on ebay I inevitably came across the pretty looking cheap Chinese ones . So I decided to come here and see what people were saying about them. I pretty much believe you get what you pay for but I want to like these things... lol, mainly for the price tag. I can get a few of em for different scenarios. So my question to you guys is... has anybody done any mods to these to improve the sound? I'm sure there's a point of where it's not cost effective but if swapping out a few compoinents that are higher quality will help make it "sound" better. I'm game. I'm not an amp guy so I dont know the internals. I'm just a user.. but I have a good ear. I may like it off the bat because I dont have much experience with HiFi tube gear, just studio and instrument tube stuff. I have a Denon AVR-3808ci that i'm using at the moment. I wouldn't mind picking up a few of these amps and sending them to one of you guys to do some mods if someones doing it.I'm sure it would be worth while

Thanks!
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Old 20th September 2011, 10:01 AM   #2
brady is offline brady  Philippines
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Hi. Not the easiest (certainly not the quickest), but you might want to check "operating point" of each tube in the amp.

This almost always require alterations in the power supply. If you are attracted to how these amps look like (and want to preserve the looks), the way to do it is to relocate the entire power supply to a separate box/chassis. And leave the tubes and output transformers as is.

Changing resistor or capacitor brand (but maintaining values) might improve things a bit.
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Old 20th September 2011, 10:30 AM   #3
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Quote:
Originally Posted by brady View Post
Hi. Not the easiest (certainly not the quickest), but you might want to check "operating point" of each tube in the amp.

This almost always require alterations in the power supply. If you are attracted to how these amps look like (and want to preserve the looks), the way to do it is to relocate the entire power supply to a separate box/chassis. And leave the tubes and output transformers as is.

Changing resistor or capacitor brand (but maintaining values) might improve things a bit.
Exactly, just a few things could make a world a difference.
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Old 20th September 2011, 10:56 AM   #4
DF96 is offline DF96  England
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Rumours suggest that some, but not all, of these cheap Chinese amps can be unsafe.

On another site someone reported that he had reason to look inside a Chinese OPT. Maybe rewinding after a failure? Anyway, he was surprised to find that the paper used as insulation layers was not high quality (with high clay content?) but had been cut from a local free advert sheet so almost newsprint 'quality'. Very hygroscopic, so asking for trouble in any but very dry air.

Expect to have to rebuild it.
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Old 20th September 2011, 12:08 PM   #5
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Quote:
Originally Posted by DF96 View Post
Rumours suggest that some, but not all, of these cheap Chinese amps can be unsafe.

On another site someone reported that he had reason to look inside a Chinese OPT. Maybe rewinding after a failure? Anyway, he was surprised to find that the paper used as insulation layers was not high quality (with high clay content?) but had been cut from a local free advert sheet so almost newsprint 'quality'. Very hygroscopic, so asking for trouble in any but very dry air.

Expect to have to rebuild it.
Lol. I dont expect much for the money. What is the next step up that's safe?
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Old 20th September 2011, 12:17 PM   #6
DF96 is offline DF96  England
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Your best bet may be to search on here and elsewhere for comments on specific items, although you would have to assume that quality has not changed since the comments were made. Unfortunately some Chinese factories change the specs/design quite frequently. You can buy the same item under different names/brandings or different items under the same name.

It is sad that it is like this, because the Chinese are capable of excellent quality when they put their mind to it or they suspect that the customer will be checking.
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Old 20th September 2011, 01:41 PM   #7
rhing is offline rhing  United States
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I bought a Chinese-made push-pull tube amplifier that was offered at a special introductory price to diyAudio.com members a while ago. The amp was advertised as an EL84 amp even though it really used Chinese 6P15P power tubes. The offer was for $150 USD including freight. It looked nice in the photos, so I figured why not? When I received the amp, the top plate was bending from the weight of the transformers, and there was no fuse on the AC (mains) inlet. For a "new" amplifier, some of the components like resistors and some caps didn't look new. I suspect they aren't. Moreover, some of us tried using EL84 tubes only to have them prematurely fail since the circuit was really built around 6P15 tubes. The manufacturer has since changed the claim that the amp can run EL84 and 6P14P tubes. The manufacturer did take some advice from diyAudio members who shared their experiences, and did incorporate some minor improvements, but then later implemented a newer design that compromised performance further at the expense of a higher selling price.

I did modify the amp I purchased and was able to extract better performance from it, but in hindsight, I would have been better off spending my $150 on a much better built vintage 6BQ5/EL84 amplifier from the U.S. and apply my DIY skills to improve it (which I later did with a Magnavox 6BQ5/EL84 amp that originally costs me $100 and it also had the original Magnavox-labeled Mullard 6BQ5 and Mullard 6EU7 tubes in excellent condition). Modifying the Chinese amp was very difficult since many transformer leads were cut to their absolute shortest lengths possible. The PCB on which the tube sockets and many circuit components were mounted was very cheap and the traces would easily pull off from the PCB during desoldering of some of the components. I still have the amp, and it sounds fine since I've replaced some of the tubes, all the electrolytic caps and the coupling caps, and tamed the cathode bias. I've made it clear on these forums that I wouldn't recommend this amp to anyone unless they like frustration and lack of communication with the manufacturer. Their newer design is worse with poorly oriented power and output transformers, power tubes mounted next to power supply capacitors, and even less space to make any decent modifications to the circuit.

I've learned my lessons and have chosen to steer clear of Chinese audio equipment sold on eBay and even here on diyAudio.com. I'm sure there are good manufacturers in China, but these deals that are "too good to be true" usually are. Instead, I buy good vintage equipment at reasonable prices and go from there, or I build from scratch. If you want a pretty Chinese chassis, buy those separately, but even then, they don't always look as good as they appear on Web sites.
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Old 20th September 2011, 07:34 PM   #8
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Good to know. I may just pick one of the $200 ones and play around with it for a while. I can always get rid of it. I was thinking of one of the 6L6 ones because I have a pair of YellowJackets tube socket converters with NOS EL84s in em. I use it for my guitar amps but I can try it with these so this way I can have 2 tones from 1 amp
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Old 20th September 2011, 07:46 PM   #9
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What about this guy? It's triple but may be worth it??

New 2011 Dared VP-20 6L6 tube monoblock amps, US limit | eBay
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Old 20th September 2011, 09:31 PM   #10
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How about this one?

tubes4hifi amplifier KITs page
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