811A tube internal resistance ? - 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 January 2004, 12:10 AM   #1
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Question 811A tube internal resistance ?

Does anybody know about the 811A internal resistance
I try to establish that datas via anode curves diagram
througt grapical method but the results are too much
differs each others that make me very suspicious...
Thanks a lot...
__________________
###
  Reply With Quote
Old 9th January 2004, 02:10 PM   #2
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Somewhere around 10k I think.
µ is extremly high so it behaves more like a pentode than a triode, sort of.
Planing on using them in an A2 amp?
Been there, done that.
  Reply With Quote
Old 9th January 2004, 08:14 PM   #3
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Yes I am planing to begin seting one amp
with a 811A...
I even found some cores by "Wasner"
for the output trans...
Actualy I have problem to aproach to
primar inductivity that is becoudse i
need to know about the Ri of the 811A
What is Your experiance you said that You build a amp with...
__________________
###
  Reply With Quote
Old 9th January 2004, 10:36 PM   #4
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Here´s the basic topology of my amp:

Triode wired E81L input stage, EL86 cathode follower direct coupled to 811A grid. I can post a more detailed schematic within a couple of days if anyone´s interested.
Attached Images
File Type: jpg 811.jpg (17.7 KB, 652 views)
  Reply With Quote
Old 10th January 2004, 09:29 AM   #5
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Thank You Fuling...I will post the settings
of my topology...soon
But on the first site I foun that
You feed the 811 from the cathode...
My intension is to put the input transformer first...
__________________
###
  Reply With Quote
Old 11th January 2004, 03:31 PM   #6
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Hi
I set the 811A at :
Ug = +15 V
Io =60 mA
Ua = 900 V
RL = 10468 ohm (10.5 Kohm)
with estimated :
Pa = 54 W
Po =12.875 W
H2 = around 0%
-A = 34.33
Ig = aroud 5 mA
Cdyn = 204 pF
that requires 5960 ohm input R for -3db at 131KHz or 19541ohm for -3db at 40KHz...
The problem is that I could not calculate the Ri from the anode curves datas and
with that value of Ri calculate Req of the output stage stage...
And when I dont have the Req proper calculated i simply could not calculate
primar inductance of the Output transformer for desired low frequencu response...That is all...
__________________
###
  Reply With Quote
Old 11th January 2004, 03:35 PM   #7
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
My results on Ri established by the graphical method,varys from :
28Kohm to 6.3Kohm...
???
__________________
###
  Reply With Quote
Old 11th January 2004, 04:50 PM   #8
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Ri is nonlinear with voltage, operating points, load, and frequency- modeling it as a pure resistance is not terribly accurate.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 12th January 2004, 02:17 PM   #9
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Of course SY...
But I have to start with something...
I am planing to try a litle simulations with a PSpice (I found a subcircuit for the 811A
tube )...
What I heard about the 811A tube from people who done somewhat with is :
That 811 in presence of DC signal behaves like decreasig the Ri rapidly...
and that is Ig increasing until the 20-40 mA ???
__________________
###
  Reply With Quote
Old 12th January 2004, 02:22 PM   #10
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
The best thing to start with is the minimum resistance that the grid will present. I'd do some measurements (pulse excitation, please!) to determine, for the tubes you're actually using, what the Ri is at the maximum expected drive voltage. That can be done with a pulse generator, an amplifier, a series resistor, and a scope.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  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
Gas Reference Tube (5651/85A1/etc) Internal Impedance kevinkr Tubes / Valves 6 3rd July 2009 09:22 PM
Automotive relays and internal resistance? pjpoes Everything Else 2 9th February 2007 04:18 PM
Re-attaching anode cap to 805 or 811A tube Jim Ricketts Tubes / Valves 5 7th June 2006 01:39 PM
Anyone know agood MOSFET drive for RCA 811A Tube? Alastair E Tubes / Valves 9 25th August 2005 03:59 PM
811a Tube Cap Size NickC Tubes / Valves 2 15th April 2004 09:47 AM


New To Site? Need Help?

All times are GMT. The time now is 09:54 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