Pentode section of 6M11 - 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 9th April 2011, 02:40 PM   #1
diyAudio Member
 
rsumperl's Avatar
 
Join Date: Oct 2009
Location: Warren Center, PA
Default Pentode section of 6M11

Morning everyone,
I came up with a plate load of 34K for the pentode section of a 6M11 (http://tubedata.milbert.com/sheets/093/6/6M11.pdf). Is this right? It seems rather low. My B+ is ~500v, though I do have ~200v available.

Thanks,
Ray
  Reply With Quote
Old 9th April 2011, 11:12 PM   #2
diyAudio Member
 
rsumperl's Avatar
 
Join Date: Oct 2009
Location: Warren Center, PA
Ok, so I experimented:
470KΩ G1 to GND
750Ω Cathode to GND (0.8V)
1.5MΩ G2 to 380V (gave me ~40V)
220KΩ Plate to 380V (gave me ~90V)
Fed plate to amplifier input with a .1UF cap and shielded cable.
SO...with G1 grounded, quiet as if it was not there, unconnected or connected to a source, very hissy, no hum though. not sure why.
Tons of gain, WAY to much gain.
At this point, unless the hiss can be managed, this tube may not be an option. I did not try another tube, perhaps this one is defective. I believe my layout was fine.

Any inputs???

Ray
  Reply With Quote
Old 9th April 2011, 11:44 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Your gain is way high. With a gm of roughly 13mA/V, 220k plate resistor, gain = 13x220 = 2860! Try dropping the plate resistor to 20k or so, and scale the screen resistor accordingly (70-80k). That will give you a high-but-possibly manageable gain of 250 or so.
__________________
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 10th April 2011, 12:18 AM   #4
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally Posted by rsumperl View Post
Tons of gain, WAY to much gain.
At this point, unless the hiss can be managed, this tube may not be an option. I did not try another tube, perhaps this one is defective. I believe my layout was fine.

Any inputs???
It's definitely a high gain pentode, and it'll produce lots of gain even operating with such low voltages. That's gonna mean noise. The high impedances also don't help in that regard either. Did you remember to include grid and screen stoppers? The "hiss" you're hearing could be an artifact of high frequency oscillation. High gain pents, like transistors (also high gain devices) are susceptible to oscillation.

What are you using this for, and how much gain do you really need?

Your other options, if you don't need the gain, are to triode the pentode section, or make an anode follower out of it. NFB will both reduce gain and noise.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 10th April 2011, 01:13 AM   #5
diyAudio Member
 
rsumperl's Avatar
 
Join Date: Oct 2009
Location: Warren Center, PA
I tried what SY mentioned, still lots of hiss. My thought was to use the pentode as a first stage of gain and then use the triodes as a phase inverter LTP. Do you think it's doable?

Ray
  Reply With Quote
Old 10th April 2011, 05:05 AM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
The gm is really high- you could be oscillating.
__________________
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

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
Differences between single-section and two-section filters Sunsun22 Power Supplies 3 20th November 2009 06:23 AM
PCF801 - pentode section has remote or sharp cut-off? ilimzn Tubes / Valves 3 31st January 2006 08:39 PM
A small no-fuss pentode/pentode SE amp Tubes4e4 Tubes / Valves 13 1st January 2006 06:16 AM


New To Site? Need Help?

All times are GMT. The time now is 04:00 AM.


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