HT PSU 120hz hum!

[kambo]

my regulated HT PSU's for my tube pres keep giving me 120Hz hum...
this is happening on not even regularly  used PSU's with TL783 regulator.
i always end up slapping a large capacitor through 5w 1r resistor at the output of PSU, and everything goes back to normal,
( i have some 450uf 400v caps in my stash)

i doubt my caps are drying out in such short period of time to cause this 120hz problem, would it be the regulator chip TL783
is getting ran down ?

what should i be looking  for to trace the problem....
also, how do i check if TL783 is basted without changing it..

example schematic from rudetube Ivory PSU...

 

[ruffrecords]

A regulator  is only as good as the raw dc it is fed with. The circuit you posted has only a 47uF reservoir capacitor which in my view is a little on the side. If you start to draw a significant current from this the then ripple will increase. The ripple is reduced significantly  by the following filter but the 4700 resistor implies it is intended for fairly low currents. Good for driving a preamp or too. For higher currents the circuit needs redesigning.

Cheers

ian

 

[gyraf]

Questions to clear up:

What is your transformer's ac voltage?

How much current are you drawing?

What are your DC voltages before and after the regulator?

How much 120Hz hum do you have - and how much is too much?

Are you aware that you loose 1.3W of power just for lighting up the LED?

Jakob E.

 

[kambo]

thanks Jakob,

i never use led on PSU... schematic is an example... i am not putting a blame on design..
i already switched to unregulated HT supply. so i cant measure!
i will hook it up off line, my guess is regulator getting fried!

 

[kambo]

after reading the TL datasheet, and going through tube datasheets, i get it now
thanks Ian,