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Title: 100th PP deck bias requirements??? Post by: KL7OF on December 02, 2005, 04:34:37 PM I have built up a PP pair of 100ths with B and W butterfly cap and HD coils... I have a separate bias supply that provides about -100V...Everything works fine with less than 2200V on the plates...They idle at 25 ma. When I turn the variac up to more than 2200V the plates start to draw about 100ma with no drive applied..and turn red in the process.... The bias supply is capable of 225 volts... I have to change out the grid bias dropping resistor (or find an adjustable one with a slider) to get the bias voltage up and that may do the trick.....I am wondering however, What is the current requirement for this bias supply?? I'm wondering if the bias xfmr I am using has enuf scrote.... All comments appreciated......By the way I am going to modulate this deck with triode connected 813s and run it on 20 meters.....
Title: Re: 100th PP deck bias requirements??? Post by: Don, W2DL on December 03, 2005, 11:03:45 AM My tube charts say at 3000 v you would need abt -65v to keep dissipation at 150w for the pair (50 ma plate current), and maybe -100 to keep it far lower. You shouldn't need anything more for protection, just use a series grid resistor to make up the operating bias needed (maybe abt -220 v or so) AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
73 Don. W2DL |