Trevor Wilson wrote:
"Andre Jute" wrote in message
oups.com...
Justin wrote:
Hello everyone! I am a newcomer to the world of tube audio. I've
loved my Peavey Classic 30 guitar amplifier for the last 6 years and
I'm looking into getting started in the world of tube stereos. I know
a little bit about amplifiers (I'm a recent EE grad) and I collect
vinyl as well.
I'm considering purchasing the amplifier listed he
http://cgi.ebay.co.uk/Nice-300B-6CA7...QQcmdZViewItem
Yo, Justin, welcome! Don't let the choleric mouthfoamers like Wilson
put you off; they count it a day wasted in which they don't ruin
someone's pleasure in being alive.
**Why? Have you heard that amp? Do you advocate that people should spend
money on products they've never listened to? You're dumber than the original
poster.
Never buy a car without test driving it, never marry a woman without first
bedding her and NEVER buy audio equipment without first listening to it. Of
course, a moron might suggest that I am wrong. Sane people will always
disagree with you.
The original poster could audition just about any 8 watt amp with 300B SET outputs
to get an idea of what is possible with 8 watts.
I am sure he could find a sample, or join an audio club to find out more.
But I do share Trevor's concerns about the chinese build quality.
Quality is something the makers of cheaper chinese don't understand like the best makers in the West.
But one has to expect this situation to be quite normal because if they are prepared to make
an amp for 20dB less $$$ than a CJ or ARC, then expect 20dB less quality.
Its about that simple.
Anyone buying Chinese Crap may need to have it modded.
About 3 weeks ago I had to repair a chinese amp from Hong Kong with
the brandname printed on the front "Hi-Fi Amplifier", which isn't a brand name.
The guy here who bought it for peanuts direct from HK got it cheap because no western middle men
upped the chinese price by 15dB.
Anyway, it lasted 2 weeks before one channel became silent.
I easily fixed it by replacing a 25 watt common cathode resistor to the two KT88 output tubes of one channel.
There was no paper work with the amp and no schematic available anywhere.
I found it difficult to trace the point to point circuitry because parts had been thoughtlessly
placed so that tube socket tags were obstructed from view, and couldn't be soldered
unless some parts were removed.
To remove the faulty resistor I had to break off bolts because the screw heads were obstructed by
the double layered steel chassis used to enable about 6 different models to be assembled
similar to the one which is the subject of this thread.
So replacement of an OPT or other part including a tube socket would take 30dBb longer than it should.
The amps are not built to be serviced easily, and as usual, contain no active protection measure should there
be bias failure of one or more output tubes.
The power transformers hummed badly, and were not silent as they should be.
There were two power trannies wired in parallel, and with 3 dual diode rectifier tubes also
wired in parallel to act as a slow turn on diode, with SS rectifiers.
It was supposed to be dual monbloc but wasn't.
As well as the gimicky 3 rectifier tubes where one would have been OK there were 2 tuning eye level indicators
which had numbers and chinese lettering and about which I could find no data on th web.
They indicated clipping at about 1/4 of actual clipping output voltage.
Good amps don't have gimicks.
The volume control pot and source switch was the usual crap $2 type one sees in cheap
shops selling such crap.
And its a nightmare to replace such items and any of the rear panel RCA sockets etc
because there is a stupid 10mm thick anodized Al panel screwed on from inside the amp to cover
any nuts or screws allowing one to replace these items.
Somebody with NO brains designs these amps which are designed to look good,
and easy to assemble, and horror story to service.
The powder coat finish was very ordinary.
The amp was UL, and made the correct 50 watts AB but there was zero NFB so the output
impedance was 10 ohms. Although the OPT had enough bandwidth with no NFB, they howled
with signal and showed that they were not properly potted and maybe not varnished properly.
The quality of circuit layout left a lot to be desired although it looked well if you had no idea about detail.
After the small mods I made to the KT88 output tube cathode circuits by using
separate R&C bypassing to each of the 4 KT88, I then converted it to triode operation and
Rout fell to 2 ohms at the 8 ohm outlet.
There was still very adequate output in triode to suit the owner's speakers from either the 4 ohm outlet
where Rout = 1 ohm, and from the 8 ohm outlet.
The 4 ohm outlet ensured class A power was around 12 watts, with slightly more in class AB,
so the amp ended up about the same as a standard 16 watt Williamson with KT88 in triode
which is the better tube to use in a Williamson, and not as much NFB need be used, and in fact
because the wacko weirdo chinese input circuit would have taken too much modding
to accomodate 12dB of loop NFB, I left that job out and left the amp without global NFB.
The owner is delighted. He now gets better HF with his Quad ESL57 because these speakers have declining
Z at HF which don't suit being driven with an amp with Rout = 10 ohms.
I would predict that perhaps another branch of rthe HK company who made the amp I
repaired may make Guchi handbags and Rolecks watches.....
But the one I repaired looks very much like the one mentioned in this thread.
It has very similar details both above and below the chassis.
I'd never buy one of course.
Photographs of chinese crap on E-bay do not show up the faults many of the
amps.
But if price is all that matters then then the Chinese are unbeatable.
And at the end of the day, the Chinese cheap amp is no worse than the crap
that was foisted upon us by unruly western makers in 1955.
One hardly has to try very hard to make OPT and power trannies better than the cheap horrors
sold by Ferguson and others here in Oz, and ones fitted to Leak amps in the 1950s.
The chinese are merely regurgitating all the past craperama without having learnt from the past
and I wish them well should they try to improve.
Its unfortuate that had the amp I fixed been built to a similar design to a Leak
in terms of chassis construction and wiring detail, it would have been a lot cheaper for the Chinese
to make! And it would have been better than a Leak.
And if the Chinese ever learnt a little more about transformers and circuitry
and parts quality they would indeed get more respect from discriminating audiophiles
all over the world.
Patrick Turner.
--
Trevor Wilson
www.rageaudio.com.au
--
Posted via a free Usenet account from http://www.teranews.com
How about this amplifier?
Linear Mode
