|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: What chcarcteristics make a good pentode driver?? posted by SLM on January 19, 2005 at 22:52:31:
Hi,> Never used pentodes before !!
Try it.
> I do not have any 310a pentodes
Well, an EF86 is electrically surprisingly similar... ;-)
> what produces a good pentode driver
Correct implementation and realistic expectations.
First great expectations....
Pentoides are in effect transconductance devices, in other words, the anode current is modulated primarily by the gridvoltage and virtually not at all by the anode voltage (the result of the screen).
As a result they have a very high output impedance and the current modulation is impressed across the Anode Resistor and load (next stage input Resistor).
Also, there is practically no supply noise rejection in the Pentode, if it's on the top of the Anode resistor, it's on the output.
Pentodes have a lot of 2nd Harmonics, WE used this deliberatly to cancel some of the output valves HD.
The rather high output impedance of the Pentode can lead to frequency bandwidth problems, there is strictly no class A2 operation, in fact, as soon as the output valve draws gridcurrent the drive voltage collapses in a heap of wet jelly.
In order to get the best sound of Pentodes I found a few basic rules:
1) Use much less than nominal anode current, try 1/2 to 1/3rd of the current given under typhical application as "Class A Amplifier" in the datasheet.
2) Have around the Bias of the output valve between screengrid and anode.
3) Have around twice the output valve bias across the anode load.
This usually gets pretty good sound. Of course, different Valves sound different.
Ciao T
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: What chcarcteristics make a good pentode driver?? - Thorsten 01/20/0506:11:26 01/20/05 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
