Soft starting the rectifier

mashaffer · 22nd October 2008, 09:21 PM

A CL150 in the B+ line after the rectifier is often used to cushion the start a little bit. Seems like a very good idea but I was wondering about putting the CL150 directly in the heater circuit between the filament and the transformer. The idea being to soft start the rectifier's filament easing the flash heating of the filament and also delaying B+ slightly. The recto in question is 5U4GB.

Thoughts?

SpreadSpectrum · 23rd October 2008, 04:02 AM

It might work if you wanted to run the heaters low. CL150 has a steady state resistance of .11 Ohms at 4.7A. That is a drop of about half a volt. The resistance increases if used with less steady state current. Maybe this could be used to correct filament voltages that are too high. Seems like it might work well with a Hammond transformer...

I usually use CL140 in B+(50 Ohms cold, 1.1A max). It seems like it would work a lot better than CL150 (5 Ohms cold, 4.7A max) in that position , unless you are pulling a heck of a lot of current. 5 Ohms cold from the 150 won't give you much benefit, either.

22nd October 2008, 09:21 PM	#1
mashaffer diyAudio Member Join Date: Jun 2004 Location: Indiana	Soft starting the rectifier A CL150 in the B+ line after the rectifier is often used to cushion the start a little bit. Seems like a very good idea but I was wondering about putting the CL150 directly in the heater circuit between the filament and the transformer. The idea being to soft start the rectifier's filament easing the flash heating of the filament and also delaying B+ slightly. The recto in question is 5U4GB. Thoughts? __________________ mike - www.keepingsundayspecial.org

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23rd October 2008, 04:02 AM	#2
SpreadSpectrum diyAudio Member Join Date: Nov 2007	It might work if you wanted to run the heaters low. CL150 has a steady state resistance of .11 Ohms at 4.7A. That is a drop of about half a volt. The resistance increases if used with less steady state current. Maybe this could be used to correct filament voltages that are too high. Seems like it might work well with a Hammond transformer... I usually use CL140 in B+(50 Ohms cold, 1.1A max). It seems like it would work a lot better than CL150 (5 Ohms cold, 4.7A max) in that position , unless you are pulling a heck of a lot of current. 5 Ohms cold from the 150 won't give you much benefit, either.

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