Troubleshooting a 6n1p linestage.

Bas Horneman · 30th March 2004, 02:54 PM

I had this first tube thing I ever built still on my site.

Someone has built it and measured it.
Apparently it drops of quite fast above 10k?

What could be the cause for this?

Regards,
Bas

Frank Berry · 30th March 2004, 02:57 PM

The output impedance is rather high.
Perhaps they are using a long cable with lots of capacitance.

Bas Horneman · 30th March 2004, 02:59 PM

Mmm yes thought it would be something like that...
Thanks Frank

I have suggested..

1.) Running more current through tube.
2.) Bypassing the cathode resistor...Lowers the impedance
3.) Try to make a cathode follower with the tube.

MaciekP · 30th March 2004, 04:38 PM

Hi,
the smaller the load resistors, the wider the frequency response gets, but inversely the higher the distortion. So, we rather choose the loading resistor between the factors of 3 to 7 times of Rp of the tube.
I think, that anode resistor, especialy for parralel tubes, are too high. The lack of cathode bypass cap should make the Rp higher and mu lower and for 1K cathode resistor it should also affect the LF...just wondering...

Maciej

fdegrove · 30th March 2004, 09:29 PM

Hi,

Maciej's quite right IMO so I redrew it a little even though it's still not the best linestage:

Cheers,

fdegrove · 30th March 2004, 11:31 PM

Hi,

Scrap the cct above, this one should be better:

Cheers,

30th March 2004, 02:57 PM	#2
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	The output impedance is rather high. Perhaps they are using a long cable with lots of capacitance. __________________ Frank

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30th March 2004, 02:59 PM	#3
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	Mmm yes thought it would be something like that... Thanks Frank I have suggested.. 1.) Running more current through tube. 2.) Bypassing the cathode resistor...Lowers the impedance 3.) Try to make a cathode follower with the tube.

30th March 2004, 04:38 PM	#4
MaciekP diyAudio Member Join Date: Mar 2004 Location: Warsaw	Hi, the smaller the load resistors, the wider the frequency response gets, but inversely the higher the distortion. So, we rather choose the loading resistor between the factors of 3 to 7 times of Rp of the tube. I think, that anode resistor, especialy for parralel tubes, are too high. The lack of cathode bypass cap should make the Rp higher and mu lower and for 1K cathode resistor it should also affect the LF...just wondering... Maciej