300B Filament Voltage Range

dsavitsk · 14th October 2005, 05:05 AM

Is it safe to run 300B's with a filament voltage of 5.23V, or is this too high?

If it is too high, does anyone have a suggestion on how to drop the voltage by a very small amount? The current draw of these particular tubes seems to be about 1.2125A necessitating either a ~ 0.19R resistor or some other means. Is a Mills 0.18R the best option?

Bas Horneman · 14th October 2005, 08:27 AM

5,23 is acceptable...but indeed dropping the voltage with a small resistors would be the best option I think..Some report slightly better sonics with just below <5V voltages.

kmtang · 14th October 2005, 01:19 PM

5.23V is within safe range for 300B's filament. However, it is good to add a small dropping resistor which would cut down the start up current.

Johnny

dsavitsk · 14th October 2005, 05:44 PM

The filament voltages were at 4.26V with a 0.8R dropping resistor. Jumpering over the resistor raised them to 5.22. Interestingly, I think the amps sounded considerably better with 4.26V. They seem to have become less lush (a little sterile sounding) as well as a bit sluggish at the higher voltage. As soon as I can get my hands on some different resistors, I am going to try for a bit under 5.

-d

Sheldon · 14th October 2005, 07:07 PM

If you can give up a little output you don't need to rule out the possibility of running at 4.26V.

http://members.aol.com/sbench102/dht.html

Sheldon

14th October 2005, 05:05 AM	#1
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	300B Filament Voltage Range Is it safe to run 300B's with a filament voltage of 5.23V, or is this too high? If it is too high, does anyone have a suggestion on how to drop the voltage by a very small amount? The current draw of these particular tubes seems to be about 1.2125A necessitating either a ~ 0.19R resistor or some other means. Is a Mills 0.18R the best option? __________________ http://www.ecpaudio.com :: http://diy.ecpaudio.com

14th October 2005, 08:27 AM	#2
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	5,23 is acceptable...but indeed dropping the voltage with a small resistors would be the best option I think..Some report slightly better sonics with just below <5V voltages. __________________ Boatanchor amps forum My "adventures" in audio

14th October 2005, 05:44 PM	#4
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	The filament voltages were at 4.26V with a 0.8R dropping resistor. Jumpering over the resistor raised them to 5.22. Interestingly, I think the amps sounded considerably better with 4.26V. They seem to have become less lush (a little sterile sounding) as well as a bit sluggish at the higher voltage. As soon as I can get my hands on some different resistors, I am going to try for a bit under 5. -d __________________ http://www.ecpaudio.com :: http://diy.ecpaudio.com

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14th October 2005, 01:19 PM	#3
kmtang diyAudio Member Join Date: Nov 2004 Location: Vancouver	5.23V is within safe range for 300B's filament. However, it is good to add a small dropping resistor which would cut down the start up current. Johnny

14th October 2005, 07:07 PM	#5
Sheldon diyAudio Member Join Date: Dec 2003 Location: San Diego	If you can give up a little output you don't need to rule out the possibility of running at 4.26V. http://members.aol.com/sbench102/dht.html Sheldon

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