Re: 6SN7 Mu Follower Distortion Paper

flipper wrote:
On Mon, 26 Jan 2009 18:28:38 +0000, Ian Bell <ruffrecords@xxxxxxxxx>
wrote:

Iain Churches wrote:
"Ian Bell" <ruffrecords@xxxxxxxxx> wrote in message
news:gktetl$dka$1@xxxxxxxxxxxxxxxxxxxxxxxx
I have written up the work I did on investigating distortion in a 6SN7 mu
follower and posted it at my website. You can read it here:

http://www.ianbell.ukfsn.org/data/mufollowerdistortion.pdf

Ian. Excellent paper.

You mentioned that you had, or were in the process
of acquiring, a HP spectrum analyser to examine the
differences between the distortion profile of the
different valves/tubes that you had tested.

Have you done this analysis yet? Some pics would be of
interest.

Not yet - I am at present struggling to get a twin T notch filter working properly so I can measure the individual harmonics. However, I can say from some initial tests without the twin T that at 20V rms the 2H level is close to -50dB, the 3H seems to be around -75dB and the third is below what my instrument will measure. So the contention that it is 'mainly second harmonic' would seem to be true.

As for pictures, the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! I have seen a suggestion of using it with a USB data capture device but one of these costs more than I paid for the HP ;-) so for the present it will just have to be done by hand.


OTOH a cheap PC interface type scope might do the trick.

Very well might and there are a couple of free ones so all it would
take is some patch cables to see.


I have tried a couple of those that use your PC soundcard on my laptop. Could not get either one of them to work properly - probably something to do with the sound chip but it is a new laptop.

No I was thinking more of those that plug into a usb port and have some external = decent electronics.


Cheers

Ian
.

Relevant Pages

  • Re: 6SN7 Mu Follower Distortion Paper
    ... a HP spectrum analyser to examine the ... You can connect it to a scope but as its scan ... I have tried a couple of those that use your PC soundcard on my laptop. ... So basically any audio stuff I have tried on my laptop have been ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... a HP spectrum analyser to examine the ... You can connect it to a scope but as its scan ... to do with the sound chip but it is a new laptop. ... Pretty much and capture too of course. ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. ... You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! ... It is a start and the spectral shape of the harmonics is the second step. ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... Ian. ... the device I have bought is an HP 3581A Wave Meter - it is in effect a spectrum analyser but not with a PC interface for capturing nice pictures. ... You can connect it to a scope but as its scan rate is of the order of seconds you wont see much on a scope unless it is a storage type and mine isn't - it will interface directly to a pen plotter though!!!! ...
    (rec.audio.tubes)
  • Re: 6SN7 Mu Follower Distortion Paper
    ... Ian. ... a HP spectrum analyser to examine the ... You can connect it to a scope but as its scan ... So basically any audio stuff I have tried on my laptop have been ...
    (rec.audio.tubes)