View Single Post
  #5   Report Post  
Andy Cowley
 
Posts: n/a
Default

Pooh Bear wrote:

Lawrence wrote:


Some people told me that a "good" and "no-so-good" 12AX7 and 12AU7 really
make a big difference to the pre-amp and power-amp.

I look at some Chinese 12AX7A which cost about US$12.00 a piece, and a
piece of Tesla ECC803S cost about US$50.00; similar goes to the 12AU7!

I wouldn't mind to pay for the difference, but I want to know if it is
worth paying that?

Can anyone ever tried that can be kind enough to share their experience?



I haven't tried it - but it would seem that you need some advice.

The ECC803S ( aka E83CC from some sources ) is a 'long life / high
reliability' type - quoted as 10,000 hrs operation. That's why it's more
expensive.

Any thermionic valve aka 'tube' has characteristic that are simply determined
by the structure of the electrodes ands the quality of the materials used.

Provided that the valve conforms to the correct electrode spacings etc - the
characteristics will be assured.

Clearly, the quality of materials used will affect usable life - hence the
premium price for your ECC803S.

In short - there is nothing about the operation of a valve that can make it's
characteristics *better* than it's *original* spec. A basic understanding of
electronic theory will help.

Don't expect brand X valve to 'sound better' than brand Y valve if they are
manufactured to original spec.


Either you are deaf or you haven't done any real comparisons. I can certainly
hear a difference between a NOS Mullard and a Chinese ECC83, even in a low-fi
guitar amp. Check out the curves from different manufacturers examples of a
specific valve. Notice that the non-linear bits at the extremes of the curves
are a little different? Try them on a distortion analyser and notice that the
relative amounts of harmonics are different. All the valves will be within spec.

The specifications given for valves are _very_ incomplete. Usually only plate
resistance, transconductance and hence mu at one or two operating points. I've
never seen a specification which even gave error limits for these three parameters
let alone anything which would pin down the linearity of the changes in these
parameters with changes in operating point.

So there very definitely is something about a valve that can make it sound
different from a differently manufactured example of the same type.

We live in a real analog world not an idealised one.

best

Andy