Re: 6SN7 Mu Follower Distortion Paper

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.

Most 6CG7s that I have evaluated have similar THD
values, and yet in comparison tests, Westinghouse
and Telefunken are usually picked out as sounding
the best. Perhaps THD does not tell us the full story.


I am sure it does not. It is a start and the spectral shape of the harmonics is the second step. After that it is looking at intermodulation distortion which I can also do on the HP.


Cheers

ian
.

Relevant Pages

  • 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!!!! ... Could not get either one of them to work properly - probably something to do with the sound chip but it is a new laptop. ...
    (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)
  • 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)