Plate current Question - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 20th June 2009, 07:07 AM   #1
diyAudio Member
Rob11966's Avatar
Join Date: Jun 2007
Location: Australia
Default Plate current Question

Here's something that confuses me.

I am talking about the 845 tube but I imagine that this question applies to other tubes as well.

With respect to the operating plate current, the ratings differ depending on the plate voltage. Looking at the 845 Amperex data for example the typical operating values are as follows (plate voltage plate current) -

750v 95mA
1000v 65mA
1250v 52mA

I understand why you have to adjust the bias voltage to limit/adjust the plate current but I don't understand why the recommended typical operating current goes down with increased plate voltage. If the plate is capable of handling 95mA at 750v, why can't it handle 95mA at 1250v? More specifically what the problem with running a tube at say 1000v and 95mA.

I am sure I have missed some basic point. Any advice appreciated.


  Reply With Quote
Old 20th June 2009, 07:18 AM   #2
rtsang is offline rtsang  Hong Kong
diyAudio Member
Join Date: Aug 2005
Default Plate dissipation

Plate dissipation = plate voltage drop x plate current

The power dissipation is the fixed value.
For 300B, it is 40W.
For 2A3, 15W.
Of course too much voltage and too much current will also kill a tube, but usually we hit the power limit first.
  Reply With Quote
Old 20th June 2009, 07:22 AM   #3
diyAudio Member
Join Date: Apr 2006
Location: Minnesota
Power dissipation limit.
  Reply With Quote
Old 20th June 2009, 08:13 AM   #4
diyAudio Member
Rob11966's Avatar
Join Date: Jun 2007
Location: Australia
Obvious - now. Thanks guys.

  Reply With Quote


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
Plate Current VS Plate Voltage Graphs Captn Dave Tubes / Valves 2 13th February 2009 08:57 PM
Plate Amp Standby Current (PE 500W/1000W) gmikol Subwoofers 6 20th February 2006 06:19 AM
Welborne 300b DRD plate current dsavitsk Tubes / Valves 0 9th September 2005 07:47 PM
El509 Plate current question audio_siuming Tubes / Valves 9 25th February 2004 11:01 PM
active plate load v.s. constant current... mwmitchell Tubes / Valves 3 8th August 2002 09:34 PM

New To Site? Need Help?

All times are GMT. The time now is 03:01 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2