Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on November 16, 2013, 08:53:42 pm
-
Hey guys, several years ago i built a Pro 5E5-A head version for a local guitar player. He brought it back the other day and said the amp works fine, but would like to get a little more volume and punch from the amp. This is what I have done after checking out his amp and speakers first: Changed V1 and V2 from 12AY7`s to 12AX7`s, Built a S/S plug-in to replace the 5U4GB rectifyer, changed the first filter cap from 16uf to 32uf, and re bias for 70% MPD. WOW! what a difference. The owner loves it. My question is: With a Pi filter (cap/choke/cap) that handles the intire amp currant, having the first filter cap twice the value the of the second filter cap cause any problems with the choke and caps down the road? I tried searching the net for info and all I found was that the first cap has to handle the highest voltage. All schematic drawings I have seen with the Pi filter show both caps being the same value. Any comments are much appreciated
Punky
-
... With a Pi filter (cap/choke/cap) that handles the intire amp currant, having the first filter cap twice the value the of the second filter cap cause any problems with the choke and caps down the road? ...
It won't cause any problems.
All schematic drawings I have seen with the Pi filter show both caps being the same value.
That generally convenience.
The power transformer and rectifier are generally chosen to deliver a desired voltage and current. The other power supply values (caps, choke) are chosen to minimize ripple, and the total of Cap*Choke ideally meets a certain minimum value.
But you can make the caps smaller and choke bigger (done in the old days when iron was cheap and capacitance expensive) or you can make the caps bigger and the choke smaller (more typical today when cost/uF is pretty low).
And if you don't have a compelling reason to use a lower-value cap somewhere in the circuit, it is cheaper to buy the same value in greater quantities. So you often see the same one value through the amp (at least for modern amps).
-
Thanks HBP, I just wanted to be sure after viewing those schematics. :icon_biggrin:
-
It is a very common thing to increase the first node to 40uf on Princeton's. Been doing it for years and never had a problem. Doubles the first filter cap, but leaves the rest stock.