Pentodes. - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd August 2009, 02:53 PM   #1
bigwill is offline bigwill  United Kingdom
diyAudio Member
 
Join Date: Dec 2004
Location: UK
Default Pentodes.

I used to subscribe to the "Triodes ONLY" school of thought for output stages, but I've recently come around to Pentodes / Tetrodes for output devices, as they have a lot of advantages, and with clever local feedback, can achieve the same or lower output impedance than triodes, with similar distortion. They can be driven in weird and wacky ways like screen drive or enhanced triode mode (not sure if anyone actually uses this though, sounds a bit tough / fatal to the screen grid)

They are much more efficient, and can make a lot more power than most pure triodes, and are easy to find

Pentodes rock! I think they get too much bad press

I'm even coming around to global negative feedback, maybe I'm going insane
  Reply With Quote
Old 2nd August 2009, 03:25 PM   #2
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
case for purchasing a Morgan Jones book. Valve amps 3rd edition. No wonder sonny boy likes his Glenfiddich.

richy
  Reply With Quote
Old 2nd August 2009, 03:27 PM   #3
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
Welcome in "real" word

Yves.
  Reply With Quote
Old 2nd August 2009, 04:10 PM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally posted by richwalters
case for purchasing a Morgan Jones book. Valve amps 3rd edition. No wonder sonny boy likes his Glenfiddich.

richy
Only if you want a clear explanation of what the problems of feedback are and ways to avoid them.

Screen drive with the right tubes is a great option. And sweep tubes are cheeeeeeeeap.

Welcome to the Dark Side.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 2nd August 2009, 04:14 PM   #5
bigwill is offline bigwill  United Kingdom
diyAudio Member
 
Join Date: Dec 2004
Location: UK
Quote:
Originally posted by richwalters
case for purchasing a Morgan Jones book. Valve amps 3rd edition. No wonder sonny boy likes his Glenfiddich.

richy

Have it already
  Reply With Quote
Old 2nd August 2009, 04:36 PM   #6
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
The secret with pentodes is the feedback, you do that right and they can sound as good as triodes.

Now i have a pp 6v6 triode amp with global negative feedback and sounds better than any se triode amp or pentode pp amp i've ever heard and i have heard many. But i don't need the power of pentodes.
Right now i am working with a pp pentode amp, the mission is to equal or better my pp triode amp. Just because i want to hear if that is possible.

People mod their Marantz and Dynaco pentode amplifiers to triode and they don't go back.

Two years ago i felt global feedback killed the soul of the recordings....how wrong i was. But feedback loops are tricky and i'm not an engineer.
Respect to people who know their trade, most dyers don't, but is still fun as a hobby.
  Reply With Quote
Old 2nd August 2009, 05:28 PM   #7
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
If you go with pentodes, you can go farther and use them in a driver.
This driver was developed to drive GU-50 pentodes, with local parallel feedback by voltage over each output tube (240K resistors from their plates to plates of drivers). After I finish my current hybrid project I am going to redesign this one a bit, and make PCBs available for DIY community, if such demand exists. Not necessary to use it with GU-50, there may be KT-88, or other high power tubes that need a voltage swing.

Click the image to open in full size.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 2nd August 2009, 05:31 PM   #8
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Default Re: Pentodes.

Quote:
Originally posted by bigwill
I used to subscribe to the "Triodes ONLY" school of thought for output stages, but I've recently come around to Pentodes / Tetrodes for output devices, as they have a lot of advantages, and with clever local feedback,

I'm even coming around to global negative feedback, maybe I'm going insane

No you aren't going insane. I've been using true tetrode/pentode output stages with GNFb for over 40 yrs. Once youv'e mastered the quirks then you can really stab power triodes or triode config pentodes in the back. However there is competition, don't forget the lower working impedance of triodes; it makes the output tranny much easier to design and that's a big bonus.

Sy mentions screen grid drive; I've always found tubes don't last long with this when compared to conventional driven p-p: there are circuits around but reliability ?
Perhaps someone can correct me on a tried and tested design.
richy
  Reply With Quote
Old 2nd August 2009, 05:35 PM   #9
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Default Re: Re: Pentodes.

Quote:
Originally posted by richwalters



However there is competition, don't forget the lower working impedance of triodes; it makes the output tranny much easier to design and that's a big bonus.
Please see my previous post.

__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 2nd August 2009, 06:20 PM   #10
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
An "All Pentodes" 300B Killer

Click the image to open in full size.

Even at clip limit H2 is still predominant:

Click the image to open in full size.


Yves.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Beam pentodes and suppressor-grid pentodes of same type jon_010101 Tubes / Valves 3 3rd May 2009 12:18 AM
6AU6 pentodes TGRANT Tubes / Valves 20 6th March 2009 01:22 AM
heater-less Pentodes Bandersnatch Solid State 2 5th August 2008 12:20 PM
triode pentodes whitelabrat Tubes / Valves 7 17th October 2007 08:46 AM
Sex, Music And Pentodes mrfeedback Everything Else 0 20th September 2002 02:39 AM


New To Site? Need Help?

All times are GMT. The time now is 09:04 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2