Need help: 5687 tubes and heat dissipation - 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 14th March 2006, 03:18 PM   #1
Mrpong is offline Mrpong  Thailand
diyAudio Member
Join Date: Aug 2004
Location: Bangkok
Exclamation Need help: 5687 tubes and heat dissipation

The schematic below is the headphone amplifer using 5687 tubes.

5687 tube headphone amplifier

In the schematic, you will see a group of 20K resistors which are my problems. Those 20K resistors are terribly hot even though we use the 3-watts type. Is this because of poor design of this schematic or because of the characteristic of 5687 tube? Any comments please?
  Reply With Quote
Old 15th March 2006, 12:59 AM   #2
diyAudio Member
Join Date: Nov 2002
What is the voltage across those resistors?
  Reply With Quote
Old 15th March 2006, 03:11 AM   #3
diyAudio Member
Brian Donaldson's Avatar
Join Date: Jan 2003
Location: Texas, Love it or leave it
They will get hot. Use ohms law and if your less than 1.5 W, just give them free air and let 'um burn. I biult a simular HP amp, but used a long tail pair input to keep absolute phase and It sounds quite nice.

  Reply With Quote
Old 15th March 2006, 03:15 AM   #4
lndm is offline lndm  Australia
diyAudio Member
Join Date: Mar 2006
Location: nsw
Knowing that voltage would be helpful.

Lets assume for a moment that the 260v rail is half across the triodes and half across the resistors. The 100 ohm resistor doesn't see much.

7 x 22k in parallel = 3k14. Now ((130v)^2)/3k14 = 5.38W.

This is not massive. Less than one watt per 3w resistor will make them hot, but not hot enough to concern over. Make sure they are separated with some airflow around them.
  Reply With Quote
Old 15th March 2006, 08:52 PM   #5
diyAudio Member
richwalters's Avatar
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
bear in mind todays resistor ratings are quoted for 70C i.e assume 50C rise at 25C ambient. Personally I find this 70C too hot so I often use a 3W resistor for a 1W circuit diss with a poorish ventilated under chassis.
Design for longevity.

  Reply With Quote
Old 15th March 2006, 10:31 PM   #6
diyAudio Member
Brian Donaldson's Avatar
Join Date: Jan 2003
Location: Texas, Love it or leave it
Aslo, dump the electrolytic on the output and buy the biggest film cap you can find. A little bass roll off is far better than the nasty grunge from the dilectric absorption of the 'lytic. Give it a listen.
  Reply With Quote
Old 20th March 2006, 03:07 PM   #7
diyAudio Member
Join Date: Jul 2005
Location: southern us
Additionally, the 5687 heater filaments consume .45 amps in series and .9 amps in parallel.

  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
A3 heat dissipation problem spTOH Pass Labs 4 3rd October 2006 05:45 AM
CLC Question - Heat Dissipation TwangBar Pass Labs 2 2nd February 2005 08:01 PM
Heat dissipation from 3875 soundNERD Chip Amps 3 19th January 2005 01:03 AM
Heat dissipation Magura Pass Labs 26 15th November 2003 12:00 PM
Class A sound/AB Heat Dissipation Samuel Jayaraj Solid State 5 23rd October 2003 12:34 PM

New To Site? Need Help?

All times are GMT. The time now is 05:50 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