tube matching question

T

tempus fugit

Guest
Hey all;

I just put 4 new tubes in my Carvin guitar amp and was wondering about
matching. The current through the cathode of the tubes is:

30mA
32mA
25mA and
36mA.

The tubes are supposed to be matched, but evidently tolerances weren't too
tight. Are these tubes "matched" enough? I guess what I want to know is
whether I should take the tubes back and get an actual matched quad, or if
it doesn't really matter a whole lot. I know about 10 years ago I replaced
the tubes and blew 3 of them in the first 6 months. I definitely don't want
that to happen again. Could the mismatch (particularly the high and the low
tube) cause that kind of problem? The power being dissipated ranges from 10w
to 16 watts, depending on the tube, so I think I'm safe as far as that goes.
Is there any reason I should be concerned about the mismatch, or should I
just leave it? I tried swapping the tubes around, and the currents were
pretty much the same, so I think I can also rule out problems with the amp's
circuitry (can't I?).

Thanks
 
If they are matched, all the symmetrical even harmonics are cancelled,
leaving the harse sounding odd harmonics. If you just mismatch them on
purpose by pullin one out, you get the nice rich bluesy sound you've
been seeking... lots of odd and even harmonics.
 
Thanks for your reply Bob.

I've read that argument also - that unmatched tubes will give a better sound
than matched ones. To be honest, the sound is fine to my ears, but I just
want to make sure that no damage will result (to amp or tubes) with the
mismatched state they're in now.


"BobG" <bobgardner@aol.com> wrote in message
news:1125341625.857476.78420@g49g2000cwa.googlegroups.com...
If they are matched, all the symmetrical even harmonics are cancelled,
leaving the harse sounding odd harmonics. If you just mismatch them on
purpose by pullin one out, you get the nice rich bluesy sound you've
been seeking... lots of odd and even harmonics.
Click to expand...
 
When a tube shorts out and draws big amps, it smokes the output
transformer primary. Big bux.
 
BobG wrote:
If they are matched, all the symmetrical even harmonics are cancelled,
Click to expand...
This isn't actually true in any typical guitar tube amp as they operate
in class AB (i.e strongly class B). Only if the output is class A will
the even harmonics be cancelled.

You need both halves to be active all the time to effect a v^2 - (-v)^2
cancellation.

Oh.. the question...the accuracy of matching noted in the original post
is reasonably ok.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Hey Kevin..... You didn't reply to my inquiry about your mic preamp
design progress.... wondering if its to the component selection and
layout stage yet....
 
BobG wrote:
Hey Kevin..... You didn't reply to my inquiry about your mic preamp
design progress.... wondering if its to the component selection and
layout stage yet....
Click to expand...
Unfortunately, I am rather busy at the moment.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
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