Need help with Fender Schematic

[Rick1114]

Can someone help me identify which filter cap in this schematic goes to the mains, the screen and the preamp? My 66' Vibrochamp recently had a cap job & the tech used 47uf across the board. From what I've been reading, this would be okay for the mains and the screen supply, but may not have a desirable effect on the preamp section, so I ordered a 22uf to replace that one. My filter caps seem to be wired up somewhat like this:




Thanks,

Rick

[TD_Madden]

All of the blue ones shown on the left of the board should be 20uF.....NOT 47uF.

Go here: http://www.thevintagesound.com/ffg/

and look at the blackface Vibro-Champ entry.

[Rick1114]

TD - I know they should be 20uf, but doubling the value of the mains or the screen supply is not always a bad thing. I just need to identify which filter cap belongs to the preamp section, because that one should probably stay at 20uf.

Thanks,

Rick

[Jag]

The one on the right

[52 Bill]

TD - I know they should be 20uf, but doubling the value of the mains or the screen supply is not always a bad thing. I just need to identify which filter cap belongs to the preamp section, because that one should probably stay at 20uf.

Thanks,

Rick

If you follow the power supply path, it's really simple. The output from the rectifier tube is first sent to the leftmost cap in your drawing, where it feeds the output transformer. Then it is dropped by the 1K resistor and goes to the second filter cap which feeds the output and driver stages. Then it is dropped by the 10K resistor and goes to the third filter cap which feeds the two 100K plate resistors of your pre-amp tube.

So the cap you are asking about is the rightmost cap in your drawing.

[Rick1114]

The one on the right

Many thanks

[Rick1114]

If you follow the power supply path, it's really simple. The output from the rectifier tube is first sent to the leftmost cap in your drawing, where it feeds the output transformer. Then it is dropped by the 1K resistor and goes to the second filter cap which feeds the output and driver stages. Then it is dropped by the 10K resistor and goes to the third filter cap which feeds the two 100K plate resistors of your pre-amp tube.

So the cap you are asking about is the rightmost cap in your drawing.

A most excellent answer - now I get it perfectly. The left feeds the power supply or mains, the second output & driver (is that called the screen supply?), and the third hits the plate resitors for the preamp tubes.

Thanks,

Rick

[Enzo]

Rick, we generally reserve the term "mains" for the AC power coming in from the wall.

The B+ system has "nodes." Basically each step on the string is a node - each filter cap mostly. The first filter after the rectifier is what I think you are calling main. We might call that the first filter, first node, or the plate supply, second node being the screens, then following nodes for the PI, preamp, whatever.