I can verify the "commercial sound" I swapped my chinese one (700 euros including customs) for a pretty expensive Italian amp in a friend's system. The difference was marginal.
And then I tore it apart and rebuilt it, pretty easy because it is point-to-point. In the process I realised thet the output transformers were not too good with feedback, the power switch was really an input selector switch, the gold plated rca's had faded, and the "heavy-duty" speaker connectors had cracked.
In any case, not a bad experience. My advice is, insist on point-to point. That way, it is easy to hack.
I have one of these amps - 6N3 into a pair of 6P1. Got it locally when the previous owner said it stopped working. A fuse replacement did the trick. I have to admit it sounds better than I expected. I do not know about the crazy 30wpc the company says it puts out (maybe at 30% THD?)
http://www.diyaudio.com/forums/swap-meet/273532-music-angel-yayi-usb-tube-amp-6n3-6p1-push-pull.html#post4306346
http://www.diyaudio.com/forums/swap-meet/273532-music-angel-yayi-usb-tube-amp-6n3-6p1-push-pull.html#post4306346
The problem with Chinese amps is their (lack) of quality control.
You never know who actually made it and what components have been used.
They are notorious for running components right up to their voltage or current limits.
This with designs rated ar 220 volts causes problems when mains runs above that.
( I had an 845 amp go up in flames.)
They can sound very good, but I would only sugest them to people who can do the required safety checks, and they could build from scratch anyway!
You never know who actually made it and what components have been used.
They are notorious for running components right up to their voltage or current limits.
This with designs rated ar 220 volts causes problems when mains runs above that.
( I had an 845 amp go up in flames.)
They can sound very good, but I would only sugest them to people who can do the required safety checks, and they could build from scratch anyway!
Well,
I purchased some years ago a pair of Cary SLM-100 amp and the issues where:
- one power transformer heat up much
- claimed for bias adjust on a local dealer, but really the where auto bias
- old design with old cap's
but sometimes is good to start with some finished (mechanical & electric) and starting to improve the existing..
Like: Wiring (several chassis earth points) , long signal paths (sorted already), cap's pealing (already done), no more auto base do the electrolytic cap's in the signal path, new power trany to drive KT120
Cheers
Hp
I purchased some years ago a pair of Cary SLM-100 amp and the issues where:
- one power transformer heat up much
- claimed for bias adjust on a local dealer, but really the where auto bias
- old design with old cap's
but sometimes is good to start with some finished (mechanical & electric) and starting to improve the existing..
Like: Wiring (several chassis earth points) , long signal paths (sorted already), cap's pealing (already done), no more auto base do the electrolytic cap's in the signal path, new power trany to drive KT120
Cheers
Hp
This is another one that I would avoid like the plague. It's all hype with really awful components.
MADE IN ENGLAND KT88 Triode Con VALVE AMPLIFIER Lim Sign AVC Affordable Valve Co | eBay
MADE IN ENGLAND KT88 Triode Con VALVE AMPLIFIER Lim Sign AVC Affordable Valve Co | eBay
Yes rotten quality control:
I had an 845 Music Angel with no mains earth, 2 x 450V rated caps in series across the +915V B+ supply with inadequate voltage sharing resistors, it blew an output tranny (primary to secondary short) which took out a choke and an 845 tube.
I had a PP EL34 Chinese Amp with different component values in the 2 channels and one channel also had the unequal anode load resistors on the differential phase splitter swapped (the larger resistor was on the input side not the cathode driven side).
The designs (as SY said above) are not designs at all but just rip offs of late 60's or early 70's designs from various manufacturers and the sort of cost compromise changes I see show a total lack of tube amp theory/knowledge.
I would not contemplate a Chinese Amp having been burned sufficiently with the 2 I've had already (both of which have failed but are not worth fixing).
Cheers,
Ian
I just bought one of these: HiFi 6P13P Vacuum Tube Amplifier Class A Single-Ended Power Amp Board DIY Kit 175864069187 | eBay because I had a good discount on it and I have a bonus on a local toroidal producer, plus I would like to see how this kind of amp can sound as is and with some mods.
This should be the schematic AFAIK:
and this the datasheet of the chinese 6P13P:
http://ds.agavaceae.ru/china/6p13p.pdf
alias russians 6P13S:
https://frank.pocnet.net/sheets/113/6/6P13S.pdf
I've seen it's supplied with 0-290 Vac, so around 400 Vdc B+, so around 30 mA at idle.
Seems too much for many reasons. The first one is the output trafos, too small IMHO. The second is that for a 14 W plate dissipation tube, 7 Wrms on SE is impossible. The third is that I would go lower in voltage in order to have a bit more class A available. Probably there are alot more.
Specifications of the OPT should be:
The model for the 6P13S is the following:
Vacuum Tube SPICE Models
This should be the schematic AFAIK:
An externally hosted image should be here but it was not working when we last tested it.
and this the datasheet of the chinese 6P13P:
http://ds.agavaceae.ru/china/6p13p.pdf
alias russians 6P13S:
https://frank.pocnet.net/sheets/113/6/6P13S.pdf
I've seen it's supplied with 0-290 Vac, so around 400 Vdc B+, so around 30 mA at idle.
Seems too much for many reasons. The first one is the output trafos, too small IMHO. The second is that for a 14 W plate dissipation tube, 7 Wrms on SE is impossible. The third is that I would go lower in voltage in order to have a bit more class A available. Probably there are alot more.
Specifications of the OPT should be:
Code:
1. Power: 3 W
2. Frequency Risposta: 20z-30KHz (-2dB)
3. Core Specifiche: EI48X24, nucleo sezione X24MM
5. Primary Impedenza: 5.5K Ω,
6. Secondario: 0-4-6-8 Ω e UV uso misuratore di livello
7. Primary Induttanza: 11 H
8. Primary resistenza: 278Ω
9. L primaria corrente: 70MA
10. Grade resistenza: 2.3 Ω
11. peso: 0.6 kg/pzThe model for the 6P13S is the following:
Vacuum Tube SPICE Models
I have some OPT very similar to those bought from ebay (I'd say identical except that I cant see a PN printed on the yellow tape, as my example has)
A non-standard pin pitch made mounting awkward
They OPT are ok; at a pinch, for Parafeed, but didnt not tolerate any DC whatsoever. LF, even in this case, was poor, due to low L.
A non-standard pin pitch made mounting awkward
They OPT are ok; at a pinch, for Parafeed, but didnt not tolerate any DC whatsoever. LF, even in this case, was poor, due to low L.
Thanks mondogenerator, indeed there's need to have less than 1.4 kOhm of internal resistance to have a -3dB point at 20 Hz.
In pentode mode 6P13S' Ri is 25 kOhm, so what I was planning, together with gnfb, was shunt feedback, cathode feedback using secondary taps, or g2 UL-like drive as posted on this forum.
This can be useful to compare some russians tubes:
http://www.next-tube.com/articles/spectr/spectrEN.pdf
In pentode mode 6P13S' Ri is 25 kOhm, so what I was planning, together with gnfb, was shunt feedback, cathode feedback using secondary taps, or g2 UL-like drive as posted on this forum.
This can be useful to compare some russians tubes:
http://www.next-tube.com/articles/spectr/spectrEN.pdf
World Audio Design amps come up on eBay in the UK for £500 up. I'm guessing the parts are pretty good. The construction could vary from a professional build to a rats nest of a home built kit, however. Get pictures of the insides!
Interesting reading with no one mentioning that higher end amps like "Jolida / Black Ice" and "Sophia Electric" are all made in China -
They were simply better at telling the Chinese manufacturers what to do / what's needed, than whoever it was that spec'd the ebay stuff.
It's only a matter of time before some place like "Douk" either goes out, or gets it right quality wise - and the laurel wreath around certain products.
That's the main difference I've seen - fit and finish and transformer quality. The rest is all Chinese build. You bet Douk would love to sell all their product for £500 and up -
They were simply better at telling the Chinese manufacturers what to do / what's needed, than whoever it was that spec'd the ebay stuff.
It's only a matter of time before some place like "Douk" either goes out, or gets it right quality wise - and the laurel wreath around certain products.
That's the main difference I've seen - fit and finish and transformer quality. The rest is all Chinese build. You bet Douk would love to sell all their product for £500 and up -
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