Question about Shishido 2A3 - 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 15th February 2012, 07:47 PM   #1
diyAudio Member
 
korneluk's Avatar
 
Join Date: Jan 2005
Location: South Florida
Default Question about Shishido 2A3

Folks,
Need some help understanding the purpose of the 22k 3W resistor between the cathode of the 2A3 and the 150K plate load/voltage dropper for the 12AX7.

Click the image to open in full size.

Thx,
  Reply With Quote
Old 15th February 2012, 08:14 PM   #2
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
By applying some positive voltage to the cathode, the correct voltage relationship between the 2A3's grid and cathode is maintained. As the tube ages, less cathode current would be drawn resulting in less negative voltage appearing on the grid. (with respect to the cathode) This is especially important because the tube's grid is directly coupled to the previous stage.
__________________
"I regard the brain as a computer which will stop working when it's components fail. There is no heaven or afterlife for broken down computers. That is a fairy story for people afraid of the dark." ~Stephen Hawking
  Reply With Quote
Old 16th February 2012, 03:39 AM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
It has to do with the fact that 195V across 3K is 65mA, so the 22K resistor provides the other 5mA so that the 2A3 doesn't have to.

The 22K resistor could be omitted if a 3250 ohm cathode resistor was used instead, in fact 3.3K is probably more than close enough. You would have to adjust the value of that 25K resistor to compensate for the greatly reduced current however. (Change to about 120K)

You might also consider a 6SL7 in the first stage, you'll only need to tweak its cathode resistor value to get the right plate current in the first stage. (I'd probably run half a 6SL7 per channel)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
Joplin PP 2A3 Question... gray49 DIY HiFi Supply 5 14th June 2011 09:12 AM
Tubelab SE 2A3 _ Newbie question. btran Tubes / Valves 14 21st November 2009 02:28 AM
WTB: OPTs for 2A3 or 45 SE; 240 v power tranny for 2A3 or 45 rick57 Swap Meet 0 8th November 2006 02:07 AM
Help about SHISHIDO Pre Phono Maurizio Analogue Source 1 9th May 2005 01:22 PM


New To Site? Need Help?

All times are GMT. The time now is 12:44 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