Load resistor on OPT - 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 3rd April 2011, 05:52 AM   #1
Tyimo is offline Tyimo  Hungary
diyAudio Member
 
Join Date: Nov 2002
Location: Hungary
Default Load resistor on OPT

Hi!
I read somewhere that even Power tube amplifiers likes to have load resistor on the secondary.
Does anybody have experience in this theme?

Tyimo
  Reply With Quote
Old 3rd April 2011, 07:58 AM   #2
diyAudio Member
 
Join Date: Apr 2011
Quote:
Originally Posted by Tyimo View Post
Hi!
I read somewhere that even Power tube amplifiers likes to have load resistor on the secondary.
Does anybody have experience in this theme?

Tyimo
Yes, in case of your amplifers have no feedback circle, special with pentode tube
  Reply With Quote
Old 3rd April 2011, 08:01 AM   #3
diyAudio Member
 
Join Date: Apr 2011
Yes, special with pentode tube, in case your amplifier have no feetback circle
  Reply With Quote
Old 3rd April 2011, 09:52 AM   #4
diyAudio Member
 
Join Date: Dec 2009
Quote:
Originally Posted by thanhtruc03 View Post
Yes, special with pentode tube, in case your amplifier have no feetback circle
How about "MK1 Very Easy Speaker", Mr Talkactive?
  Reply With Quote
Old 3rd April 2011, 03:30 PM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Valve amplifiers like to have some load. If not, clipping can induce big voltages in the output transformer which cause insulation breakdown. Every few weeks, someone pops up on here and says that he thinks he may have blown his amp (often a guitar amp) by accidentally running it with no speaker connected.

The presence of feedback won't help, it could make it worse because when the output stage clips the feedback loop will try to drive it even harder.
  Reply With Quote
Old 3rd April 2011, 06:32 PM   #6
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by DF96 View Post
Valve amplifiers like to have some load. If not, clipping can induce big voltages in the output transformer which cause insulation breakdown. Every few weeks, someone pops up on here and says that he thinks he may have blown his amp (often a guitar amp) by accidentally running it with no speaker connected.

The presence of feedback won't help, it could make it worse because when the output stage clips the feedback loop will try to drive it even harder.
DF96,

There have been a lot of discussions on how to protect the Tx. It seems to be easier on a PP amp you can go across the two plate connections with MOV. However on SE the situation is different, a MOV trip would cause B+ short. Was there ever a definitive answer regards SE?

Regards
M. Gregg
__________________
What is the sound of one hand clapping?
  Reply With Quote
Old 3rd April 2011, 07:23 PM   #7
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
I used 1/4 inch jacks that have internal switch for when nothing is plugged in. I wired the switch so when no speakers are plugged in it feeds the output into 25 watt 8 ohm(in my case) resistors in my single ended pentode amp. Of course this does nothing if both ends of your wire are disconnectable and you unplug the speaker side

Last edited by ryuji; 3rd April 2011 at 07:26 PM.
  Reply With Quote
Old 3rd April 2011, 07:27 PM   #8
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by ryuji View Post
I used 1/4 inch jacks that have internal switch for when nothing is plugged in. I wired the switch so when no speakers are plugged in it feeds the output into 25 watt 8 ohm(in my case) resistors in my single ended pentode amp.
Interesting,

It's another way around the problem!


Regards
M. Gregg
__________________
What is the sound of one hand clapping?
  Reply With Quote
Old 3rd April 2011, 07:36 PM   #9
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
Would a 100 ohm resistor be enough load to damp the big voltage spikes that
dammage the transformer insulation?
  Reply With Quote
Old 3rd April 2011, 07:51 PM   #10
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by woody View Post
Would a 100 ohm resistor be enough load to damp the big voltage spikes that
dammage the transformer insulation?
What you have to remember is how much of the output you are loosing as wasted heat. OK with this you are only dropping resistance by a small amount. It would probably work however you would not know until you get a speaker disconnected.

Regards
M. Gregg
__________________
What is the sound of one hand clapping?
  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
Resistor as a load ixe13 Tubes / Valves 12 2nd September 2010 08:15 PM
Proper load resistor for I/V secondary? phrarod Digital Line Level 9 15th July 2010 01:03 PM
Plate load resistor question Carlp Tubes / Valves 14 21st January 2008 02:41 PM
Driver stage load resistor Klimon Tubes / Valves 3 18th October 2006 10:26 AM
Understanding OPT primary Z and load matching. percy Tubes / Valves 4 21st August 2004 01:30 AM


New To Site? Need Help?

All times are GMT. The time now is 10:01 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