Can bigger first PS- filter Cap lead to higher Noise?

[DerEber]

Hey ho,

After my last tube amp recap I have the following question in my head for days now.
In this amp (Siemens 100V) I changed the filter caps. The old ones had gone bad leaving the output tubes with the bare rectified AC.
Now those original Caps were 2x 16uF. I was only able to get 2x 47uF.
After everything was done, I  am having the impression that the buzz in this amp is now higher than before.
Of course I can not compare to the original caps. They died.

Now what I am thinking is that the 2x47uF do not discharge that much during one circle, but the circuit is sucking the same power.
This power needs to be charged into the cap in a shorter period of time. Also ESR will be lower than with the original caps.
So it will lead to bigger current spikes. So I am thinking maybe this couples into the rest of the Amp somehow.
So would you give it a try to find lower value caps?
Or is a bigger Filtercap simply better than a smaler one?

I attached a picture for your pleasure

best Greetings,
DerEber

 

[ruffrecords]

A lot depends on whether the HT rectifier is a tube or semiconductor. If it is a tube the upping the value of the first capacitor is bad news. All rectifier tubes have a recommended maximum first capacitor value. Exceeding this value will shorten the life of the tube.

If the rectifier is semiconductor then upping the capacitor will reduce the ripple on the HT. However, it will also reduce the transformer efficiency by conducting more current for a shorter period. Usually transformer efficiency is not an issue but the side effects can be. The increased spikes caused by the semiconductor turning off can find their way into the HT supply making it sound buzzy.

Cheers

Ian

 

[JohnRoberts]

+1 to what Ian said.. Larger cap will present lower impedance to transformer while charging, so all else equal peak current will be higher.

This higher peak current may be the source of your noise.

JR

 

[abbey road d enfer]

In an ideal implementation, a bigger cap should give better filtering, but when the charge current is allowed to pollute the signal ground, it's often the contrary. In many p2p realisations, the negative pole of the smoothing caps is returned to a less than ideal "ground".
You may experiment with a piece of wire attached to the negative pole of the smoothing caps and touching different points of the circuit ground. You will probably find that it changes noise, often increasing it, but with some luck it would decrease.

 

[DerEber]

Good points!
As I am currious I ordered some lower value caps and will check it out myselfe.
If it is not leading to succes I´ll try the other things you mentioned.

best greetings,
DerEber