voltage inrush at power up question

[catnine]

I have a AA764 build and saw somwhere on this site back in 2006 about adding a 47 ohm resister between the rect tube pin 8 and the first filter cap.

I measured my voltage on power up with the volt meter on the first cap and saw 750 VDC for a second then it was down to the 390 VDC B+ . The caps are 500 volt caps .

Is this something all amps have going on power up ? I never felt a concern before until I googled voltage surge. I would imagine my old 73 SF champ did the same thing .

[catnine]

I used the digital meter as a dummy , got out the analog and 390VDC sweep and never above that .

[skipm45]

The analog meter is too slow to catch the transient that occurs on start -up. The brief period of higher voltage that you observed is real.
The 47 ohm resistor will limit the inrush current to the first power supply cap prolonging rectifier life.


Skip
www.skipzcircuits.com (http://www.skipzcircuits.com)