Troubleshooting a 6n1p linestage.

[Bas Horneman]

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]

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

 

[Bas Horneman]

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]

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]

FROM THAT OTHER FRANK....

Hi,

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

Cheers,😉

 

[fdegrove]

Hi,

Scrap the cct above, this one should be better:

Cheers,😉