resistors across the heater voltage then the middle is grounded

jarthel · 9th June 2006, 04:23 AM

is there a reason for this?

thank you.

DigitalJunkie · 9th June 2006, 04:38 AM

It's to refrence the heaters to ground,and help reduce hum.
Many times a wire wound "Hum Pot" was used instead,with the wiper to ground,you just adjusted the pot untill the hum was gone (or at it's lowest level.)

jarthel · 9th June 2006, 05:08 AM

Quote:

Originally posted by DigitalJunkie
It's to refrence the heaters to ground,and help reduce hum.
Many times a wire wound "Hum Pot" was used instead,with the wiper to ground,you just adjusted the pot untill the hum was gone (or at it's lowest level.)

thank you for the explanation

lndm · 9th June 2006, 06:28 AM

If I could just add to this, does anyone have a procedure for nulling whilst using discreet resistors? Any idea how far from centre is common and how much noise reduction is expected?

jarthel · 9th June 2006, 09:52 AM

would it be okay if i use 2 75ohm 2W? if not, what value would you suggest?

thanks

Craig405 · 9th June 2006, 09:56 AM

I have seen 100 ohm as a standard value for this, going by that i would say 75 ohm would do exactly the same job.
The 2W rating is fine for 6.3V heaters.

Regards
Craig

jarthel · 9th June 2006, 10:02 AM

Quote:

Originally posted by Craig405
I have seen 100 ohm as a standard value for this, going by that i would say 75 ohm would do exactly the same job.
The 2W rating is fine for 6.3V heaters.

Regards
Craig

but for 5V, higher current rating is required?

Craig405 · 9th June 2006, 10:04 AM

Nope 5V will dissipate even less power in the resistors it will also be fine.

Regards
Craig

jarthel · 9th June 2006, 10:07 AM

thanks for the help

lndm · 9th June 2006, 10:21 AM

For what it's worth, I have a spec sheet that recommends this. It is for the 46, with a 2.5V filament. According to RCA, the resistance from end to end should be 20 ohms for this device.

9th June 2006, 04:23 AM	#1
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	resistors across the heater voltage then the middle is grounded is there a reason for this? thank you.

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
DC Heater Voltage	Bengali	Tubes / Valves	9	2nd February 2009 04:19 AM
heater voltage	Jaap	Tubes / Valves	3	18th November 2008 11:39 PM
Too low heater voltage?	jkeny	Tubes / Valves	6	26th August 2008 12:08 AM
AC or grounded DC for heater?	rouslan	Tubes / Valves	1	18th August 2006 02:16 PM
DHT and resistors in parallel w/ heater	yagoolar	Tubes / Valves	13	7th November 2004 08:17 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

9th June 2006, 04:38 AM	#2
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	It's to refrence the heaters to ground,and help reduce hum. Many times a wire wound "Hum Pot" was used instead,with the wiper to ground,you just adjusted the pot untill the hum was gone (or at it's lowest level.)

9th June 2006, 06:28 AM	#4
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	If I could just add to this, does anyone have a procedure for nulling whilst using discreet resistors? Any idea how far from centre is common and how much noise reduction is expected?

9th June 2006, 09:52 AM	#5
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	would it be okay if i use 2 75ohm 2W? if not, what value would you suggest? thanks

9th June 2006, 09:56 AM	#6
Craig405 diyAudio Member Join Date: Jul 2005 Location: Sussex	I have seen 100 ohm as a standard value for this, going by that i would say 75 ohm would do exactly the same job. The 2W rating is fine for 6.3V heaters. Regards Craig

9th June 2006, 10:04 AM	#8
Craig405 diyAudio Member Join Date: Jul 2005 Location: Sussex	Nope 5V will dissipate even less power in the resistors it will also be fine. Regards Craig

9th June 2006, 10:07 AM	#9
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	thanks for the help

9th June 2006, 10:21 AM	#10
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	For what it's worth, I have a spec sheet that recommends this. It is for the 46, with a 2.5V filament. According to RCA, the resistance from end to end should be 20 ohms for this device.

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