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Old 14th October 2005, 05:05 AM   #1
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Default 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?
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Old 14th October 2005, 08:27 AM   #2
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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.
If you can see the speaker cone move...it's not hifi.
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Old 14th October 2005, 01:19 PM   #3
kmtang is offline kmtang  Canada
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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.

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Old 14th October 2005, 05:44 PM   #4
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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.

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Old 14th October 2005, 07:07 PM   #5
Sheldon is offline Sheldon  United States
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If you can give up a little output you don't need to rule out the possibility of running at 4.26V.


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