811a Class A2 - Page 2 - 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 26th December 2002, 02:43 PM   #11
halojoy is offline halojoy  Sweden
On Hiatus
 
Join Date: Nov 2002
Arrow 15W Single End 6550C

15W Single End 6550C
from same site

15W Single End 6550C

All KITS at Elektro Akustik

/halo
  Reply With Quote
Old 26th December 2002, 05:44 PM   #12
Colt45 is offline Colt45  Serbia
diyAudio Member
 
Join Date: Feb 2002
Location: Canada
Send a message via ICQ to Colt45
I've seen A2 designs based on the 811 before.

generally a stage or two of gain, and then a hefty tube, CF directly to the grid of the 811

I'll try and see what i can find
  Reply With Quote
Old 5th March 2003, 05:27 PM   #13
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Default First try

Hi all,

This is going to be the (first) tryout for my 811A-class A2 amp.
Any comments are very welcome !!!!

Greetings
Jim
Attached Images
File Type: jpg 811-2.jpg (27.5 KB, 2126 views)
  Reply With Quote
Old 5th March 2003, 06:02 PM   #14
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
I think you're going to have a problem with a 33k resistor in the cathode of an EL84, no?
  Reply With Quote
Old 5th March 2003, 06:24 PM   #15
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Joel

Quote:
I think you're going to have a problem with a 33k resistor in the cathode of an EL84, no?
Why so ?
The EL84 anodecurrent flows into the grid of the 811A.

Jim
  Reply With Quote
Old 5th March 2003, 06:49 PM   #16
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
How much do you calculate is going through the 33k?

Also, where is the 280k grid resistor connected to?
  Reply With Quote
Old 5th March 2003, 08:37 PM   #17
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Joel,

The current through the 33k resistor is approx. 1 mA.
The 280k resistor goes to the bias supply (adjustable between
5-30V)

Jim
  Reply With Quote
Old 5th March 2003, 10:18 PM   #18
diyAudio Member
 
Join Date: Feb 2003
Location: Birmingham, UK
I think that the problem is probably a mistake on the circuit diagram - it shows Ig at 20-26ma, which implies a voltage of over 660 volts on the grid of the 811A, obviously impossible! With a current of only 1ma passing through the 33k resistor that would give a voltage of 33 on the 811A grid, a much more reasonable figure.
  Reply With Quote
Old 6th March 2003, 11:12 AM   #19
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Default Class A2 !!

Hi all,

The 20-26mA flows into the grid of the 811A,
just as the arrow indicates.
The anodecurrent of the EL84 splits into 20mA for
the 811A and approx. 1mA for the 33k resistor.

Jim
  Reply With Quote
Old 6th March 2003, 11:20 AM   #20
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
Default Re: Class A2 !!

Quote:
Originally posted by jim
Hi all,

The 20-26mA flows into the grid of the 811A,
just as the arrow indicates.
The anodecurrent of the EL84 splits into 20mA for
the 811A and approx. 1mA for the 33k resistor.

Jim
When you've got it running, try a CCS as the CF load. I think it's perfect for this application, and will likely result in lower distortion and more stable bias under dynamic conditions. One of Gary Pimm's BBMCCS would be what I'd try.

{added later} Or (read Kimmel's article below, and) run the EL84 as a pentode CF.
http://laplaza.taos.nm.us/~fvuotto/mustage.html

Just a thought.

I'm interested to see how this comes out. The Russian 811A's are reputedly at least as good as the NOS US ones, and are very cheap.
  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
811a Opt GK Tubes / Valves 20 19th May 2008 01:08 PM
811A amp Class A2 MartinV56 Tubes / Valves 9 19th October 2007 04:34 PM
811 vs 811A? Ryssen Tubes / Valves 6 12th March 2007 10:11 PM
PP Amp using 811A rwellerson Tubes / Valves 13 1st February 2007 11:55 PM
Schematic needed 811a Class A2 mario2005 Tubes / Valves 8 7th May 2006 04:01 PM


New To Site? Need Help?

All times are GMT. The time now is 12:13 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