Testing Amplifiers - Speaker or dummy load - Page 4 - 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
Thread Tools Search this Thread
Old 27th September 2010, 04:44 PM   #31
diyAudio Member
porkchop61's Avatar
Join Date: Aug 2004
Location: Mansfield, Connecticut
Originally Posted by Wavebourn View Post

A dummy load as an attenuator for a speaker.

I have a lot of 20 Ohm resistors. If to connect 5 of them in parallel it is 4 Ohm in total, for higher power. If to add computer fans for forced cooling they will dissipate even more power without a problem.


Thanks for those pictures! I was just going to recycle an old small form factor PC. Now I have a use for it!
"Imagination is more important than knowledge"
  Reply With Quote
Old 27th September 2010, 08:17 PM   #32
diyAudio Member
Globulator's Avatar
Join Date: Aug 2004
Location: Cambridge, England.
If you use NFB over more than one stage this is an interesting experiment to do:

1) Create an A/B switch so you can switch between speaker and resistive load.
2) Connect a scope probe to a signal within the feedback loop
3) Setup a square wave (500Hz etc - to suit)

Then look at the wave shape change as you switch between the resistor and speaker!
  Reply With Quote
Old 28th September 2010, 03:17 AM   #33
diyAudio Member
boywonder's Avatar
Join Date: Jan 2008
Location: So.Cal.
Originally Posted by chrish View Post
Along the lines of this discussion, I have tried to source some reasonably priced high wattage 8R resistors, but my usual sources are always out of stock. I do have a pair of 6R 50W that I have been using. Is this going to induce big errors in my testing?

Chris: At the risk of stating the obvious, if your output transformers have 4 ohm or 8 ohm taps, then a 6R load will not reflect the proper load to the output tubes, it'll either be a little high or a little low, depending on the tap. Pretty much like a loudspeaker...

So your theoretical load line/bias point and what you measure on the scope are going to be a little different.....and you've got to divide by 6 instead of 4 or 8 to determine output power.
  Reply With Quote
Old 28th September 2010, 12:46 PM   #34
chrish is online now chrish  Australia
diyAudio Member
chrish's Avatar
Join Date: Oct 2003
Location: Sydney
Since that post I managed to get some 8R 50 Watt resistors. I mounted each on a piece of heatsink I parallel them for 4R.
  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
Power load, dummy load (pic) luka Power Supplies 43 9th February 2012 02:50 PM
Tri Dummy Load raudio1969 Parts 0 25th February 2009 01:14 AM
A simple active DC dummy load for PSU testing Bootstrapper Power Supplies 42 17th August 2008 08:57 PM
dummy load reddish75 Solid State 72 3rd April 2008 01:15 AM
Dummy - load JensRasmussen Solid State 24 23rd February 2007 01:04 PM

New To Site? Need Help?

All times are GMT. The time now is 02:48 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2