G2 overvoltage ??

puginfo · 29th July 2009, 03:13 PM

i just got this cct using 6550 PP fired up with B1+ of 465Vdc wrt common gnd with rectifier but without the 12AU and AX plugged in.

did a quick check on the G2 and found its at 465Vdc as well wrt to gnd. i shut if off quickly as the 6550 specs says G2 max is 400V. isnt the 6K// resistors (3k total) insufficent to drop the voltage or is it the way i measured it which was wrong?

the OPT is hammond 1650R, 40% UL. is something really out here?

can someone pls help? thks

SY · 29th July 2009, 03:25 PM

In triode and UL (your circuit), the rating is 500V for 6550. Your measurements are correct.

puginfo · 30th July 2009, 04:13 AM

SY, thks for input. looks like all 3 voltages at the OPT pins are the same 465Vdc. wouldnt this make the config as penthode as well? attached below.

SY · 30th July 2009, 04:18 AM

No, it's not a pentode. In triode, the screen and the plate swing the same AC voltage with respect to the cathode. In pentode, the screen stays fixed with respect to the cathode while the plate swings. In ultralinear, the screen swings lees than the plate but more than zero; it's somewhere between triode and pentode.

Think AC, not DC.

29th July 2009, 03:25 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	In triode and UL (your circuit), the rating is 500V for 6550. Your measurements are correct. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

30th July 2009, 04:18 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	No, it's not a pentode. In triode, the screen and the plate swing the same AC voltage with respect to the cathode. In pentode, the screen stays fixed with respect to the cathode while the plate swings. In ultralinear, the screen swings lees than the plate but more than zero; it's somewhere between triode and pentode. Think AC, not DC. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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