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 28th November 2010, 10:41 PM   #1
diyAudio Member
 
Join Date: Nov 2010
Location: England Hertfordshire
Default max current draw according to loadlines and reality

Hello all,
ok this may seem quite a stupid question but if i was building a power amp with 4 output tubes, do i need a transformer that can supply every milliamp of current shown by loadlines? the datasheet for an el84 using 8ka-a output needs max 150mA (at 300v/Za-a/4), and then halving the output transformer and adding another tube means i would need about 300mA. am i thinking along the right lines? (no pun intended)

thank you in advance
Kind regards
razorrick1293
  Reply With Quote
Old 28th November 2010, 11:04 PM   #2
diyAudio Member
 
Join Date: Apr 2006
Location: Minnesota
razorrick,

I won't say this is a stupid question, but I don't understand it. You need to be more specific and maybe post a schematic.

Perhaps, there are folks who know what you are talking about and they can help you. I can't.

Rick
  Reply With Quote
Old 28th November 2010, 11:09 PM   #3
diyAudio Member
 
Join Date: Nov 2010
Location: England Hertfordshire
sorry, i dont have much of a schematic, im trying to design based on the instructions on this website. the loadlines drawn on the datasheet graphs go up to 150mA. then for a second tube in parallel with the first one i would assume you need twice as much current. but then do you need a transformer that can supply exactly that amount of current? more? or could i get away with supplying less current?

The Valve Wizard -Push-Pull
  Reply With Quote
Old 28th November 2010, 11:59 PM   #4
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Do you mean to parallel output toobs for twice of power?

Sure, you will have twice of current: both idle and peak, so transformers should have twice lower primary impedance and twice higher current capabilities, for twice higher power.
__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 29th November 2010, 04:26 AM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I assume you are actually asking about the current rating of the power supply and transformer? Many hifi manufacturers scrimped on the power transformer current ratings and used transformers rated for continuous operation at about 70% of maximum power consumed, and this may be reasonable in your application depending on what it is being used for.

In your case a 250mA (DC) CCS rated transformer ought to do the job fine if average power consumption is no more than that. Short term peaks can be accommodated provided the winding resistances are not high enough to adversely impact short term voltage regulation - in guitar amp applications sag is considered desirable. (I'd experiment with a 200mA transformer for guitar use..)

Higher current ratings are very reasonable in that they result in cooler transformer operation and lower noise. If ventilation is marginal an upsized PT is recommended and this would also be the case if line voltages tend to be high.. (I tend to go this way..)

Note that there is common precedent, well actually worse than this - just look at any Dynaco Stereo 70 amp, each channel idles at 100mA, maximum current consumption per channel IIRC is >200mA and the rectifier is rated at 250mA, and I doubt the original power transformer is rated any higher than this.. And they don't break all that often..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan

Last edited by kevinkr; 29th November 2010 at 04:29 AM.
  Reply With Quote
Old 29th November 2010, 06:30 AM   #6
diyAudio Member
 
Join Date: Nov 2010
Location: England Hertfordshire
ok thanks for the help, i just dont want my transformer to turn into a few useless coils
  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
Current Draw microsim444 Power Supplies 0 17th December 2009 07:36 PM
current draw of a chipamp jarthel Chip Amps 2 13th July 2007 11:45 AM
Current rating and tube current draw cbutterworth Tubes / Valves 1 13th October 2006 04:42 AM
current draw on a gainclone? cowanrg Chip Amps 9 9th August 2003 06:58 AM
Opamp current draw 5th element Solid State 2 21st July 2003 12:11 AM


New To Site? Need Help?

All times are GMT. The time now is 05:49 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