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tube matching question

T

tempus fugit

Jan 1, 1970
0
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
 
B

BobG

Jan 1, 1970
0
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.
 
T

tempus fugit

Jan 1, 1970
0
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.
 
B

BobG

Jan 1, 1970
0
When a tube shorts out and draws big amps, it smokes the output
transformer primary. Big bux.
 
K

Kevin Aylward

Jan 1, 1970
0
BobG said:
If they are matched, all the symmetrical even harmonics are cancelled,

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
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
B

BobG

Jan 1, 1970
0
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....
 
K

Kevin Aylward

Jan 1, 1970
0
BobG said:
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....

Unfortunately, I am rather busy at the moment.


Kevin Aylward
[email protected]
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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