"Steve" wrote in message
...
I bought a Chinese valve amp (Yaoin 300B job), on Ebay. Like this one:

http://cgi.ebay.co.uk/300B-High-End-...QQcmdZViewItem

It worked great for quite a while and I enjoyed the sound.
Now the left channel has gone dodgy. The music is still barely "there",
but all scratchy and weak. The right channel is fine.
I've swapped leads and connectors to establish that the speakers/cables/CD
player are not at fault. It definitely seems to be the amplifier. The left
output valve doesn't get as hot as the right one. Swapping the valves
indicates that the valve is not the problem.

Can anyone suggest a solution (other than using it as the world's heaviest
paperweight)?

I live in the North West of England. Is there anyone in the region who
could fix it?

Thanks for any help.


I have fixed quite a few of 'em in the past year. They usually have
simple but sometimes terminal (i.e fatal) faults. They range from
simple dry solder joints, or failed coupling caps, or intermittent
bias pots, to open circuit windings on the OPT.

The are people on RAT (rec.audio.tubes) who will probably been able
to pinpoint the fault from your description and further
discussion. Patrick Turner is especially knowledgeable, but holds
most Chinese products in low esteem. Many of them use poor quality
components and woefully poor/small transformers, which are hidden
inside large impressive-looking pots, sometimes filled with cat litter as a
potting compound.

At least you have one working channel, one which you can take DC
voltage measurements and compare with the broken channel. That's
the fastest way to fault find. But take great care. Even with the amp
switched off and unplugged there can still be high voltages on the
power supply capacitors.

Recently, while in Vietnam - I cam across a tube amp shop in Saigon.
I told the salesman I was interested in buying in quantity, and he offered
me "any ten amplifiers for USD1000" I have a feeling there would
also have been considerable room for negotiation in that price!!

One cannot even buy a proper UK built 300B output transformer
for the price of a complete Chinky amplifier.. Caveat emptor:-)

It's good that people are interested in thermionic audio, but sadly
they may get the wrong impression regarding reliability from a
Chinese-built product.

Tube amps can and should be reliable. I have a friend in Sweden
who is a bespoke amp builder. He offers a ten year warranty on
his work. He has been in business some twenty years, and has never
had amp returned for more than routine service.

Good luck

Iain