Need help: 5687 tubes and heat dissipation

Mrpong · 14th March 2006, 04:18 PM

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?

Original Burnedfingers · 15th March 2006, 01:59 AM

What is the voltage across those resistors?

Brian Donaldson · 15th March 2006, 04:11 AM

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.

enjoy

lndm · 15th March 2006, 04:15 AM

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.

richwalters · 15th March 2006, 09:52 PM

bear in mind todays resistor ratings are quoted for 70°C i.e assume 50°C rise at 25°C ambient. Personally I find this 70°C too hot so I often use a 3W resistor for a 1W circuit diss with a poorish ventilated under chassis.
Design for longevity.

richj

Brian Donaldson · 15th March 2006, 11:31 PM

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.

dr._sleep · 20th March 2006, 04:07 PM

Additionally, the 5687 heater filaments consume .45 amps in series and .9 amps in parallel.

dr._sleep

14th March 2006, 04:18 PM	#1
Mrpong diyAudio Member Join Date: Aug 2004 Location: Bangkok	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?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
A3 heat dissipation problem	spTOH	Pass Labs	4	3rd October 2006 06:45 AM
CLC Question - Heat Dissipation	TwangBar	Pass Labs	2	2nd February 2005 09:01 PM
Heat dissipation from 3875	soundNERD	Chip Amps	3	19th January 2005 02:03 AM
Heat dissipation	Magura	Pass Labs	26	15th November 2003 01:00 PM
Class A sound/AB Heat Dissipation	Samuel Jayaraj	Solid State	5	23rd October 2003 01:34 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

15th March 2006, 01:59 AM	#2
Original Burnedfingers diyAudio Member Join Date: Nov 2002	What is the voltage across those resistors?

15th March 2006, 04:11 AM	#3
Brian Donaldson diyAudio Member 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. enjoy

15th March 2006, 04:15 AM	#4
lndm 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.

15th March 2006, 09:52 PM	#5
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	bear in mind todays resistor ratings are quoted for 70°C i.e assume 50°C rise at 25°C ambient. Personally I find this 70°C too hot so I often use a 3W resistor for a 1W circuit diss with a poorish ventilated under chassis. Design for longevity. richj

15th March 2006, 11:31 PM	#6
Brian Donaldson diyAudio Member 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.

20th March 2006, 04:07 PM	#7
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	Additionally, the 5687 heater filaments consume .45 amps in series and .9 amps in parallel. dr._sleep

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)