Drive stage
Hi,
May I ask why you want to use penthodes in a driver stage?
Most of the times the too-high gain and high output impedance are reasons not to use penthodes in a driver stage. You can connect g2 to anode to make triodes if you have a bunch of them lying around that you want to use.
You can make a nice mu-stage, with a penthode as anode load.
Greetings,
Ray.
Hi,
May I ask why you want to use penthodes in a driver stage?
Most of the times the too-high gain and high output impedance are reasons not to use penthodes in a driver stage. You can connect g2 to anode to make triodes if you have a bunch of them lying around that you want to use.
You can make a nice mu-stage, with a penthode as anode load.
Greetings,
Ray.
There are times when the characteristics of a pentode driver stage such as high output impedance are useful.
Pentode driver stage design is really no different to triode driver stage design, just remember that Ik = Ia + Ig2, and provide a g2 supply. Also, some care or clever circuitry is required when using them in SE, since they have no PSRR to speak of.
Pentode driver stage design is really no different to triode driver stage design, just remember that Ik = Ia + Ig2, and provide a g2 supply. Also, some care or clever circuitry is required when using them in SE, since they have no PSRR to speak of.
The anode load determines (to a close enough approximation) the output Z of the pentode stage. Use high transconductance tubes and low load them. For examples see Pete Millett's pentode tests and Thorsten's Legacy amp. Built several amps using similar topologies and they are way better sounding than most triode driver stages, especially when you need a fair amount of gain and drive as you can do it both in one stage with a pentode. And often have a lower output Z from the driver stage and a lower capacitive load looking into the driver.
Thorsten partially explains his logic on the Legacy page, and also in a number of posts on Audio Asylum a couple of years back. Do a search on the tube-DIY forum under his name with pentode as a search word. There are a few interesting threads then. Ditto for a search for Pete Millett.
The rest of it is standard design with pentodes stuff that's covered in RDH and maybe Morgan Jone's book.
The rest of it is standard design with pentodes stuff that's covered in RDH and maybe Morgan Jone's book.
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