Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

E-Linear, P-P pentode application
E-Linear, P-P pentode application
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 6th December 2015, 05:58 PM   #1
stephenl5 is offline stephenl5  United States
diyAudio Member
 
Join Date: May 2011
Location: Marlborough, MA
Default E-Linear, P-P pentode application

I was reading a few old threads here regarding E-Linear.

I'm interested in trying this in a P-P Pentode amp. I have a 50W, 6K6 pri. OT with 40% taps. I prefer the sound of pentode over UL... So can I just feed the plates of a 12AX7/AT7 LTPI from the UL taps.

Does each UL tap get connected to the corresponding LTPI triode or crossed over to the opposite triode.

The feedback from the UL taps seems like it would be too much, but I assume it gets attenuated by thr plate load resistors?
  Reply With Quote
Old 7th December 2015, 07:20 PM   #2
Paul Scearce is offline Paul Scearce  United States
diyAudio Member
 
Join Date: Feb 2012
You could modify an E-Linear design by wiring the output tubes as pentodes, and connecting the driver tube loads to the corresponding UL taps. This will essentially be the same as using 40% Schade type feedback.
  Reply With Quote
Old 7th December 2015, 10:11 PM   #3
stephenl5 is offline stephenl5  United States
diyAudio Member
 
Join Date: May 2011
Location: Marlborough, MA
Thanks for the reply Paul.

I'm interested in how to calculate the amount of feedback in the loop.

It seems like the feedback from the 40% taps would be quite large compared to what is typically taken from the OT secondary. Is it hard to make it stable or do the plate load resistors attenuate it sufficiently? I think I read that hi Ra tubes are preferred...
  Reply With Quote
Old 8th December 2015, 07:09 PM   #4
nerdorama is offline nerdorama  United States
diyAudio Member
 
Join Date: Aug 2005
Location: Seattle
Here is an e-linear amp with the output tubes running in pentode mode with a regulated screen voltage. I modified a Dynaco ST-70 to e-linear using both pentodes (6AU6) and high mu triode (6GK5) driver tubes. I liked that audio quality but had a hard time with hiss in the amp. I've never figured it out but the pentodes were worse than the triodes and they were quite microphonic.

6CB5A/EL84 amp | Audiokarma Home Audio Stereo Discussion Forums
Good luck with your project.
John
  Reply With Quote
Old 11th December 2015, 02:32 AM   #5
Paul Scearce is offline Paul Scearce  United States
diyAudio Member
 
Join Date: Feb 2012
The feedback, distortion reduction, and impedance reduction are all roughly .4 times the gain of the output tubes. The load impedance seen by the driver tube is also reduced by the same amount. Stability shouldn't be an issue, since the feedback loop only includes one tube.
  Reply With Quote
Old 12th December 2015, 12:56 AM   #6
stephenl5 is offline stephenl5  United States
diyAudio Member
 
Join Date: May 2011
Location: Marlborough, MA
Thanks John & Paul,

So do I still use "typical" values for the plate resistors for a given triode in the LTPI... 100k for 12AX7?
  Reply With Quote
Old 13th December 2015, 01:55 AM   #7
Paul Scearce is offline Paul Scearce  United States
diyAudio Member
 
Join Date: Feb 2012
Modifying a typical P-P pentode design by simply attaching the load of the drivers to the transformer taps may work, but no guarantees. The ac voltage at the plates of the drivers will be the same as before, but the ac current will be considerably more, and some care must be taken that the drivers can meet this new demand. Otherwise, the amp may not be able to reach full power, and the drivers could distort.

On the other hand, modifying an existing E-Linear design to pentode operation should be as simple as connecting the output tubes as pentodes.
  Reply With Quote
Old 13th December 2015, 02:43 PM   #8
nerdorama is offline nerdorama  United States
diyAudio Member
 
Join Date: Aug 2005
Location: Seattle
Quote:
Originally Posted by stephenl5 View Post
Thanks John & Paul,

So do I still use "typical" values for the plate resistors for a given triode in the LTPI... 100k for 12AX7?
You may have to recalculate the anode load for the drivers since the UL tap might very likely be at a higher voltage. Otherwise you will probably have both higher current and a higher plate voltage on the driver. I've been through this a couple of times on an old Dynaco ST-70 that I converted to E-linear.

John
  Reply With Quote
Old 14th December 2015, 12:31 AM   #9
stephenl5 is offline stephenl5  United States
diyAudio Member
 
Join Date: May 2011
Location: Marlborough, MA
Thanks John,
Would you happen to have a schematic to share for the ST70 you converted?
  Reply With Quote

Reply


E-Linear, P-P pentode applicationHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ultra-Linear vs. Pentode Longevity BRSHiFi Tubes / Valves 60 6th March 2016 09:12 PM
Most linear triode-strapped pentode revintage Tubes / Valves 203 2nd January 2014 02:57 PM
ECF801 Triode/Pentode any useful application ? payloadde Tubes / Valves 7 3rd March 2013 08:03 PM
ultra linear aikido with linearizing pentode Jehan Tubes / Valves 0 12th October 2012 01:06 AM
Are PPA15 reasonably linear for OB application? freddi Multi-Way 1 10th December 2006 10:18 AM


New To Site? Need Help?

All times are GMT. The time now is 10:45 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki