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 30th April 2011, 11:44 AM   #1
diyAudio Member
 
rvrazvan's Avatar
 
Join Date: Jul 2010
Default Pentode driving a SE triode? any experience?

A few people suggested me to use a pentode in the driving stage of a set amp(6c33).
My initial goal was to use only triodes but this has it's own list of disatvantages. Usuing small double triodes means haven at least 2 stages..or a SRPP(wich is a for of push pull?).
Ho to pentodes sound in the driver stage? Is it a good trade to have just one pentode driving stage vs 2 triode stages?
  Reply With Quote
Old 30th April 2011, 01:20 PM   #2
brady is offline brady  Philippines
diyAudio Member
 
Join Date: Mar 2005
Location: Cebu City
Hi R. just an opinion. DHTs require sizeable amount of current, and low Z drivers --- both not usually a characteristic in pentodes. but then again, only way to find out is to try ....hehehehe
  Reply With Quote
Old 30th April 2011, 02:26 PM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Something like a D3A, C3G or 7788 running at around 15 - 20mA into a low resistance plate load might do the job fairly well.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 30th April 2011, 05:43 PM   #4
diyAudio Member
 
the_manta's Avatar
 
Join Date: Nov 2006
Location: Munich, Bavaria
Quote:
Originally Posted by brady View Post
Hi R. just an opinion. DHTs require sizeable amount of current, and low Z drivers --- both not usually a characteristic in pentodes. but then again, only way to find out is to try ....hehehehe
That counts for small signal type Pentodes like EF86.

A Pentode's characteristics are very similar to a MOSFET which can (I think nobody will deny) drive loads with a very low Z and swing huge currents.

And thats the Point that matters, the transconductance and the allowed cross current. That's the interesting property about pentodes, you don't quiet need more parameters, couse of the very high Zi. Triodes are much more complicated because of their Anode control ratio "punching" through the grid.

EF86 has a transconductance of only 2 mA/V. As a pentode, its Zi is very high and is mostly determined of the Anode Resistor.
But the 6Э5П for example has a transconductance of over 30mA/V and takes currents up to 100mA. This small russian pentode is a great tube for a very low price. (http://www.cqham.ru/tubes/soviet/scan/6ee5p.gif)
This thing is like 15 EF86 in parallel. And you can indeed drive nearly everything with it. Problem is the max. anode voltage of 250V. But when using an Anode choke not even that is a Problem.

As kevinkr said, there are many other high gm tubes wich are used succesfully to drive DHT's and sound in my ears better than staged Triodes. Those staged drivers have significant amaounts of high order harmonics wheras a single Pentode driver's harmonics mostly shows K3 and K2.
Here two 300B examples with pentode drivers (german): 300B-SE-Amp von Thorsten Loesch and SHM 002 SE

Quote:
Originally Posted by rvrazvan
Hi R. just an opinion. DHTs require sizeable amount of current, and low Z drivers --- both not usually a characteristic in pentodes. but then again, only way to find out is to try ....hehehehe
Describing SRPP would fill pages here. Short reply:Yes, you can see it as Push pull but I like the view as bootstrapped grounded cathode amplifier. Lower tube is standard anode follower and upper tube helps its Anode to swing the voltage. Read more about it at John Broskie's page.

And yes, you have to try explaining won't convince ears.
Have fun :-)
  Reply With Quote
Old 30th April 2011, 06:58 PM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by the_manta
Lower tube is standard anode follower and upper tube helps its Anode to swing the voltage.
Not quite. SRPP lower valve is standard grounded cathode, not anode follower. Upper valve helps to supply more current to the load. The SRPP and grounded cathode/bootstrapped CF are closely related, as you say.
  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
pentode in triode mode SE vs a DHT SE like 2a3/300b jarthel Tubes / Valves 62 1st January 2013 09:14 PM
C3g driving 2a3: Triode or pentode? Klimon Tubes / Valves 7 15th May 2009 10:31 AM
A directly heated triode or Pentode SE amp on a Budget avisa Tubes / Valves 24 7th March 2009 11:16 PM
Screen Driven Dissimilar Pentode SE Anti-Triode Spud kenpeter Tubes / Valves 2 26th July 2008 02:22 AM
SE Pentode or PP Triode ? percy Tubes / Valves 37 8th October 2004 10:21 AM


New To Site? Need Help?

All times are GMT. The time now is 06:15 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