Help: Western Electric 418A tubes wire in triode ? - 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 1st March 2012, 01:17 AM   #1
diyAudio Member
 
Join Date: Jun 2010
Default Help: Western Electric 418A tubes wire in triode ?

Could someone tell me how to wire the Western Electric 418A in triode ?

I want to use this tube for a preamp.
Attached Files
File Type: pdf WE-418A.PDF (85.5 KB, 104 views)
  Reply With Quote
Old 1st March 2012, 01:38 AM   #2
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Simply connect pin 5 (screen) to pin 2 (plate). You could use a small value resistor of about 100 ohms to do this, but It's probably not necessary.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 1st March 2012, 01:44 AM   #3
diyAudio Member
 
Join Date: Jun 2010
Thanks for the help.

Could you tell me what is the appropriate primary impedance of output transformer for this tube ?
  Reply With Quote
Old 2nd March 2012, 01:19 AM   #4
diyAudio Member
 
Join Date: Jun 2010
I want to use output transformers with this tube.
Can someone tell me what is the appropriate primary impedance?
  Reply With Quote
Old 2nd March 2012, 02:20 AM   #5
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
In order to provide a proper answer, more information is needed including operating points and triode plate curves. I doubt very much if triode curves for this tube exist. While I was in the surplus tube business for years, and have an extensive tube data library, I've never seen WE triode curves for any of their pentodes.

Further complicating matters is the fact that this is not a popular WE tube and I suspect few builders have ever worked with it. Also, most all WE tubes are unique unto themselves and have no close generic counterparts to compare to.

Given all of this and the knowledge that triode connecting most any pentode lowers the plate impedance, if I had a gun to my head, I would guess a load impedance of somewhere between 2500 to 5000 ohms would be close. But it's only a guess.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 2nd March 2012, 02:41 AM   #6
diyAudio Member
 
astouffer's Avatar
 
Join Date: Jun 2004
Location: Pittsburgh, crumbling wasteland
I built an amp with 429A pentodes and found them to be hit or miss in how well they work. One tube just starts to work well when the grid is sitting at 0 volts The others seem weak overall and don't bias close to what the specs say. The bad tube works better when the heater is run a few volts higher but it probably has a bad vacuum. I tried "cooking" it at higher currents but it always settled back.
  Reply With Quote
Old 2nd March 2012, 02:54 AM   #7
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Looking at the datasheet for the 418A, can calculate the triode Mu off the bottom page 3 graph of plate current versus grid voltage as around 30 to 35 approx. (depending on current op.)

http://www.scottbecker.net/tube/sheets/084/4/418A.pdf

Then assuming the triode gm is the same as the pentode gm at any given op. current, one should be able to calc. the triode plate Rp from Mu = gm * Rp.
So at 50 mA, 33 = .0265 * 1245 => 1245 Ohms Rp, an estimate anyway.
Lower current will decrease gm and raise Rp as the Ip^.5 power roughly, or derive from the graphs.
__________________
I want a Huvr-Board!!

Last edited by smoking-amp; 2nd March 2012 at 03:16 AM.
  Reply With Quote
Old 2nd March 2012, 03:43 AM   #8
diyAudio Member
 
Join Date: Jun 2010
Thanks guys for the information.
  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
Western Electric 396A tubes Andy Bartha Swap Meet 0 31st March 2011 08:53 PM
Western Electric 374A john Tubes / Valves 4 21st December 2005 03:17 PM
Western electric VT1 tubes battradio Tubes / Valves 7 19th January 2004 03:29 AM
Western Electric PassFan Tubes / Valves 0 26th April 2003 01:09 PM


New To Site? Need Help?

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