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Old 23rd March 2005, 12:43 AM   #1
MlinarS is offline MlinarS  Canada
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Default Question on design

Hello everyone,

Please help me locate any site where newbie would be able to learn driver stage design using PENTHODES.

Many Thanx.
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Old 23rd March 2005, 09:00 AM   #2
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Default 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.
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Old 23rd March 2005, 11:24 AM   #3
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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.
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Old 23rd March 2005, 01:09 PM   #4
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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.
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Old 23rd March 2005, 01:54 PM   #5
MlinarS is offline MlinarS  Canada
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Default Re: Drive stage

[QUOTE]Originally posted by 6h5c
[B]Hi,

May I ask why you want to use penthodes in a driver stage?

I want to build The Legacy by Thorsten.

Quote:
Originally posted by audiousername

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.
That is exactly the reason I want to learn about this subject as much as I can.

Quote:
Originally posted by Brett
Pete Millett's pentode tests and Thorsten's Legacy amp.

Thanks for the link.

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.
I heard to that they sound very good. So that is one of the reasons I chose to takle this priject. The second reason is I have all the parts to buid this amp.

I can easily coppy Thorsten's design, thanks Thorsten for putting it on the Forum, but that is not realy what I want. I want to learn and understand the reasoning behind this design.

Thakx everibody for reply.
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Old 23rd March 2005, 02:00 PM   #6
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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.
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Old 23rd March 2005, 02:29 PM   #7
MlinarS is offline MlinarS  Canada
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Quote:
Originally posted by Brett
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.
Thanks Brett. I'll do the search. Do you know where I can get RDH.
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Old 23rd March 2005, 04:52 PM   #8
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I don't know about penthodes, but pentodes are simple enough to use. Just think FET with screen grid (extra input!).

Tim
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Old 23rd March 2005, 07:17 PM   #9
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Quote:
Originally posted by MlinarS
Do you know where I can get RDH.
Copyright expired so some nice people have scanned it in and made it available on-line... i don't have the URL handy thou.

dave
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Old 23rd March 2005, 07:39 PM   #10
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Quote:
Originally posted by Sch3mat1c
I don't know about penthodes
But that was what Philips originally called them...

Oh, a link to RDH4 for MilnarS.
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